Journal articles on the topic 'Jet spread angle'

The k-ε turbulent model and VOF methods were used to simulate the three-dimensional turbulence jet. Numerical simulations were carried out for three different kinds of jets in a bounded pool with the deflection wall with angles of 0°, 3°, 6°, and 9°. The numerical simulation agrees well with the experimental data. The studies show that the length of the potential core zone increases with the increase of the deflection angle. The velocity distribution is consistent with the Gaussian distribution and almost not affected by the deflection angle in potential core zone. The decay rates of flow velocity in the transition zone are 1.195, 1.281, 1.439, and 1.532 corresponding to the unilateral deflection angles, 0°, 3°, 6°, and 9°, respectively. The decay rates of velocity in the transition zone are 1.928 and 2.835 corresponding to the bilateral deflection angles 3° and 6°. It is also found that the spread of velocity is stronger in the vertical direction as the deflection angles become smaller. The spread rates of velocity with unilateral deflection wall are higher than those with bilateral deflection walls in the horizontal plane in the pool.

By means of ANSYS-CFX, the 3D numerical simulations of flow field for the three hydraulic models are performed. Through comparing the three types of pumps with three different rectangle channel impellers which have different spread angle, blade, the authors draw conclusions: the distribution of the pressure and velocity in the rectangle flow channels with 6° spread angle is well-proportioned, the head and the efficiency of the whole pump can meet the requirement: But the other two types of impeller channels, the distribution of velocity is unstable, there are backflow and big whirlpool. Therefore, the rectangle channel impeller with 6°spread angle is a better type for the Roto-Jet pump.

Abstract Inclined jet air cooling can be effectively used for cooling of electronics or other such applications. The non-confined air jet is impinged and experimentally investigated on the hot target surface to be cooled, which is placed horizontally. Analysis and evaluations are made by introduction of a jet on the leading edge and investigated for downhill side cooling to identify cold spots. The jet Reynolds number in the range of 2000 ≤ Re ≤ 20 000 is examined with a circular jet for inclination (Θ) of 15 < Θ < 75 degree. Also, the consequence of a jet to target distance (H) is explored in the range 0:5 ≤ H/D ≤ 6.8. For 45 degree jet impingement, the maximum Nusselt number is widely spread. Location of maximum Nusselt number is studied, which indicates cold spots identification. At a higher angle ratio, the angle is the dominating parameter compared to the Reynolds Number. Whereas at a lower angle ratio, the inclined jet with a higher Reynolds number is giving the cooling point away from leading edge. It is observed that for a particular angle of incident location of maximum Nusselt Number, measured from leading edge of target, is ahead than that of stagnation point in stated conditions.

Using fluidic self-excited jets increases the rate of fluid mixing and reduces fuel consumption in industry burners (torches) and combustion chambers. The geometry of such jets is an important factor for fluidic jet determination. This study is concerned with investigating the types of fluidic nozzles configuration. The effect of nozzle configuration types was studied on various parameters such as frequency, velocity profile, velocity decay rate, the half angle of jet spread, and entrainment ratio. Maximum frequency and excited oscillation amplitude of fluidic jets were observed in the original geometry configuration. Also, the maximum spread rate and minimum velocity profile were observed in this geometry. Velocity decay rate shows its maximum magnitude in the original geometry configuration. Turbulence intensity reaches its maximum value in this geometry without any internal nozzle, whereas it shows the minimum value at geometry with an additional wall along the internal nozzle. The maximum increase in the half angle of jet spread was seen in the original geometry configuration. In this geometry, entrainment ratio is less than one, while in the geometry to create steady jets, entrainment ratio is more than one.

Planar jets are used for many applications including heating, cooling, and ventilation. Generally, a planar jet provides good mixing within an enclosure. In building applications, the jet provides both thermal comfort and adequate indoor air quality. Increased mixing rates may reduce short circuiting of conditioned air, eliminate dead zones within the occupied zone, reduce energy costs, increase occupant comfort, and increase indoor air quality. This article discusses how an infrared imaging system was used to demonstrate how jet excitation affected the spread angle and the jet mixing efficiency. Infrared imaging captures a large number of data points in real time (over 50,000 data points per image) providing significant advantages over single-point measurements. We used a mesh screen with a time constant of approximately 0.3 seconds as a target for the infrared camera to detect temperature variations in the jet. The infrared images show that excitation of the jet caused increased jet spread. Digital data reduction and analysis show changes in jet isotherms and quantify the increased mixing caused by excitation.

Purpose – The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to investigate the effect of variation of the angle of inclination of the wall on the flow structure of the wall jet. Design/methodology/approach – The high Reynolds number two-equation κ− model with standard wall function is used as the turbulence model. The Reynolds number considered for the present study is 10,000. The Reynolds averaged Navier-Stokes (RANS) equations are used for predicting the turbulent flow. A staggered differencing technique employing both contravariant and Cartesian components of velocity has been applied. Results for distribution of wall static pressure and skin friction, decay of maximum streamwise velocity, streamwise variation of integral momentum and energy flux have been compared for the cases of α=0°, 5°, and 10°. Findings – Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, vorticity contour and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Similarity of streamwise velocity and the velocity parallel to the oblique wall has been observed in the developed region of the wall jet flow. A decaying trend is observed in the variation of total integral momentum flux in the developed region of the wall jet which becomes more evident with increase in oblique angle. Developed flow region has indicated trend of similarity in profiles of streamwise velocity as well as velocity component parallel to the oblique wall. A depression in wall static pressure has been observed near the nozzle exit when the wall is inclined and the depression increases with increase in inclination. Effect of variation of oblique angles on skin friction coefficient has indicated that it decreases with increase in oblique angle. Growth of the outer and inner shear layers and spread of the jet shows linear variation with distance along the oblique wall. Decay of maximum streamwise velocity is found to be unaffected by variation in oblique angle except in the far downstream region. The streamwise variation of spanwise integral energy shows increase in oblique angle and decreases the magnitude of energy flux through the domain. In the developed flow region, streamwise variation of centreline turbulent intensities shows increased values with increase in oblique angle, while turbulence intensities along the jet centreline in the region X<12 remain unaffected by change in oblique angles. Normalized turbulent kinetic energy distribution highlights the difference in turbulence characteristics between the wall jet and reattached offset jet flow. Near wall velocity distribution shows that the inner region of boundary layer of the developed oblique wall jet follows a logarithmic profile, but it shows some difference from the standard logarithmic curve of turbulent boundary layers which can be attributed to an increase in skin friction coefficient and a decrease in thickness of the wall attached layer. Originality/value – The study presents an in-depth investigation of the interaction between the jet and the inclined wall. It is shown that due to the Coanda effect, the jet follows the nearby wall. The findings will be useful in the study of combined flow of wall jet and offset jet and dual offset jet on oblique surfaces leading to a better design of some mechanical jet flow devices.

HighlightsThe flow behavior of water jets discharged from different orifices was investigated.High-speed photography (HSP) was used to obtain surface structures and spread characteristics of water jets.The deformation process in axis switching related to the corner vortices effect of non-circular jets was researched by numerical simulation.The axis switching of non-circular jets enhances entrainment ability of the jet.ABSTRACT. Low-intermediate pressure sprinkler irrigation systems are important research topics in the field of water-saving irrigation. Non-circular nozzles improve spray uniformity at lower pressures and are key components of sprinkler irrigation systems. In this article, the behavior of discharged water jets from nozzles with circular, square, and equilateral triangular orifices designed with the same flow rate was investigated. High-speed photography (HSP) was used to capture jet characteristics in the near field (z&lt;20D). The largest spread angle was obtained for the square jet, which was on average 37% larger than that of the circular jet. In addition, numerical simulations were performed to analyze the axis-switching process using the large-eddy simulation (LES) method and the coupled level-set and volume of fluid (CLSVOF) method. The axis-switching phenomenon was observed in non-circular jets, in which surrounding air mixed with the jet and promoted the formation of thin diaphragm structures. The deformation process that occurs in axis switching is described according to the simulated vorticity and velocity fields. The research results suggest the axis-switching phenomenon is induced by corner vortex motions produced by the polygonal orifice, which accelerate the decay of the axial velocity and increase the jet entrainment rate. Thus, the effect of corner vortices should be considered in the design of polygonal nozzles. Keywords: Axis switching, High-speed photography, Liquid jet, Low-intermediate pressure sprinkler irrigation, Non-circular nozzle, Numerical simulation.

We report on Hubble Space Telescope imaging of eleven young stellar objects in the nearby Taurus molecular clouds. The high spatial resolution and stable point spread function of HST reveal important new details of the circumstellar nebulosity of these objects. Three sources (HH 30, FS Tau B, and DG Tau B) are resolved as compact bipolar nebulae without a directly visible star. In all three cases, jet widths near the sources are found to be 50 AU or less. Flattened disk structures are seen in absorption in HH 30 and FS Tau B, and in reflection about GM Aur. Extended envelope structures traced by scattered light are present in HL Tau, T Tau, DG Tau, and FS Tau. The jet in DG Tau exhibits a large opening angle and is already resolved into a bow-like structure less than 3″ from the star.

This article discusses gas turbine efficiency, which is an essential but often unappreciated aspect of turbomachine design pitch. To an engineer, the pitch of a turbo machinery blade is the angle at a representative blade cross-section between the blade chord line and the plane of the blade’s rotation. An axial flow gas turbine consists of many rows of rotating blades, interspersed with rows of stationary airfoils, called vanes or stators. The gas turbine compressor (whose first row of rotating blades in a jet engine may be a fan) draws in air, which after passing through a combustor to add energy to the air flow, powers the turbine which drives the compressor. Most modern commercial jet engines are turbofan, with a front mounted fan, whose size is indicated by the bypass ratio. During the 1990s, jet engine companies developed and tested variable pitch turbofans, with cycle studies showing between 6 and 14% fuel savings. If fuel savings could spread through the airline industry, changing the pitch could lead to air carriers singing a happier tune.

An experimental investigation was designed to test the hypothesis that all axisymmetric turbulent free jets become asymptotically independent of the source conditions and may be described by classical similarity analysis. Effects of initial conditions were studied by varying jet exit boundary conditions and the global density ratio. The exit velocity profile and turbulence level was changed by using both pipe and nozzle flow hardware. Initial density differences were imposed by using three gases: helium, methane, and propane. The scalar field (concentration) in the momentum-dominated regime of the far field (10 to 60 jet exit diameters downstream) of turbulent free jets was characterized using Rayleigh light scattering as the diagnostic. The results show that regardless of the initial conditions axisymmetric turbulent free jets decay at the same rate, spread at the same angle, and both the mean and r.m.s. values collapse in a form consistent with full self-preservation. The means and fluctuations follow a law of full self-preservation in which two virtual origins must be specified. The two displacements are required to account for the effects of a finite source of momentum and different development of the velocity and mass distributions in the near fields of the jets. The memory of the jet is embodied in these two virtual origins.

The exciting development of gravitational wave (GW) astronomy in the correlation of LIGO and VIRGO detection of GW signals makes possible to expect registration of effects of not only binary black hole (BH) coalescence but also binary neutron star (NS) merging accompanied by electromagnetic (gamma ray burst; GRB) signal. Here we consider the possibility that an NS, merging in an NS–NS or NS–BH system might be (soon) observed in correlation with any LIGO–VIRGO GWs detection. We analyze as an example the recent case of the short GRB170817A observed by Fermi and integral. The associated optical transient (OT) source in NGC4993 implies a rare near source, a consequent averaged large rate of such events (almost) compatible with expected NS–NS merging rate. However the expected beamed GRB (or short GRB) may be mostly aligned to a different direction than ours. Therefore, even soft GRB photons, spread more than hard ones, might be hardly able to shower to us. Nevertheless, a prompt spiraling electron turbine jet in largest magnetic fields, at the base of the NS–NS collapse, might shine by its tangential synchrotron radiation in spread way with its skimming photons shining in large open disk. The consequent solid angle for such soft disk gamma radiation may be large enough to be nevertheless often observed.

Today in Ukraine and the world there is a growing shortage of commercial fuels for engines. This is due to the tendency to regulate the production of hydrocarbons, which is the main raw material for their production. Therefore, in order to reduce oil imports, alternative fuels for diesel engines based on oils and animal fats are be-coming more widespread today. In this regard, intensive work is underway to convert internal combustion engines to biofuels in countries with limited fuel and energy resources, as well as in highly developed countries that have the ability to purchase liquid energy. Biodiesel fuel (biodiesel, RME, RME, FAME, EMAG, etc.) is an environmentally friendly type of biofuel obtained from vegetable and animal fats and used to replace petroleum diesel fuel. In the process of using RME B100 biodiesel fuel on the Renault 2.5 DCI engine, the average diameter of the fuel droplets is increased and the flare opening angle is reduced. This leads to impaired fuel distribution in the areas of the spray torch. Only 50% of the fuel is in the jet shell, which leads to impaired mixing of fuel with air. In the core of the wall there is 18% of fuel, which will spread along the walls and mix poorly with air. The remaining 36% of the fuel will be in the core of the jet, the front of the free jet and the areas of intersection of the near-wall streams, and will partially participate in the mixing. The use of biodiesel fuel RME B100 leads to a delay of heat by 18-20 degrees of rotation of the crankshaft, which will increase fuel consumption and reduce engine power. Thus, according to studies of the Renault 2.5 DCI engine on commercial and biodiesel RME B100, it is established that the use of biodiesel leads to a deterioration of the mixture due to reduced heat and as a result increases fuel consumption, reducing engine power.

Abstract. The absorption cross section of N2O5, σN2O5(λ, T), which is known from laboratory measurements with the uncertainty of a factor of 2 (Table 4-2 in (Jet Propulsion Laboratory) JPL-2011; the spread in laboratory data, however, points to an uncertainty in the range of 25 to 30%, Sander et al., 2011), was investigated by balloon-borne observations of the relevant trace gases in the tropical mid-stratosphere. The method relies on the observation of the diurnal variation of NO2 by limb scanning DOAS (differential optical absorption spectroscopy) measurements (Weidner et al., 2005; Kritten et al., 2010), supported by detailed photochemical modelling of NOy (NOx(= NO + NO2) + NO3 + 2N2O5 + ClONO2 + HO2NO2 + BrONO2 + HNO3) photochemistry and a non-linear least square fitting of the model result to the NO2 observations. Simulations are initialised with O3 measured by direct sun observations, the NOy partitioning from MIPAS-B (Michelson Interferometer for Passive Atmospheric Sounding – Balloon-borne version) observations in similar air masses at night-time, and all other relevant species from simulations of the SLIMCAT (Single Layer Isentropic Model of Chemistry And Transport) chemical transport model (CTM). Best agreement between the simulated and observed diurnal increase of NO2 is found if the σN2O5(λ, T) is scaled by a factor of 1.6 ± 0.8 in the UV-C (200–260 nm) and by a factor of 0.9 ± 0.26 in the UV-B/A (260–350 nm), compared to current recommendations. As a consequence, at 30 km altitude, the N2O5 lifetime against photolysis becomes a factor of 0.77 shorter at solar zenith angle (SZA) of 30° than using the recommended σN2O5(λ, T), and stays more or less constant at SZAs of 60°. Our scaled N2O5 photolysis frequency slightly reduces the lifetime (0.2–0.6%) of ozone in the tropical mid- and upper stratosphere, but not to an extent to be important for global ozone.

1. The feathers at the wing tips of most birds that soar over land separate both horizontally and vertically in flight to form slotted tips. The individual feathers in the slotted tips resemble the winglets used on the wing tips of some aircraft to reduce induced drag. 2. A wing that produces lift leaves a pair of vortex sheets in its wake. Wing theory shows that winglets can reduce the kinetic energy left in the vortex sheets, and hence the induced drag, by spreading vorticity both horizontally and vertically. 3. This paper describes the aerodynamic forces on a wing made of a base wing and different wing tips. The feathered wing tip was slotted and was made of four primary feathers from a Harris' hawk (Parabuteo unicinctus). The Clark Y tip was unslotted and was made of balsa wood shaped to a Clark Y aerofoil. The balsa feather tip was slotted and was made of three balsa wood wings shaped like feathers. 4. The base wing in a wind tunnel at an air speed of 12.6 m s-1 generated upwash angles as high as 15° at the end of the wing when the angle of attack of the wing was 10.5°. The feathered tip responded to upwash by increasing its lift to drag ratio (L/D) by 107 %, from 4.9 to 10.1, as the angle of attack of the base wing increased from 4° to 14°. The L/D values of the balsa feather tip and the Clark Y tip increased by 49 % and 5 %, respectively, for the same change in angle of attack. 5. With the angle of attack of the base wing fixed at 13°, changing the angle of attack of the wing tip changed the drag of the base wing. The drag of the base wing increased by 25 % as the angle of attack of the Clark Y tip increased from 0° to 15°. The base wing drag decreased by 6 % for the same change in the angle of attack of the feathered tip. 6. The total drag of the wing with the feathered tip was 12 % less than that of a hypothetical wing with the same lift and span, but with tip feathers that did not respond to upwash at the end of the base wing. This value is consistent with wing theory predictions on drag reduction from winglets. 7. Wings with the tip and the base wing locked together had lift and drag that increased with increasing base wing angle of attack, as expected for conventional wings. Span factors were calculated from these data - a large span factor indicates that a wing has low induced drag for a given lift and wing span. The wing with the Clark Y tip had a span factor that decreased from 1 to 0.75 as the angle of attack of the base wing increased. Over the same range of angle of attack, the span factor of the wing with the feathered tip remained constant at 0.87. As the angle of attack of this wing increased, aerodynamic forces spread the feathers vertically to form slots. With fully formed slots, the wing had a higher span factor than the wing with the unslotted Clark Y tip. 8. Flow visualization with helium-filled bubbles showed that the addition of two winglets to the tip of a model wing spread vorticity both horizontally and vertically in the wake of the tip. 9. These observations taken together provide strong evidence that the tip slots of soaring birds reduce induced drag in the sense that the separated tip feathers act as winglets and increase the span factor of the wings.

SUMMARYTwo barn swallows (Hirundo rustica) flying in the Lund wind tunnel were filmed using synchronised high-speed cameras to obtain posterior, ventral and lateral views of the birds in horizontal flapping flight. We investigated wingbeat kinematics, body tilt angle, tail spread and angle of attack at speeds of 4–14ms−1. Wingbeat frequency showed a clear U-shaped relationship with air speed with minima at 8.9ms−1(bird 1) and 8.7ms−1 (bird 2). A method previously used by other authors of estimating the body drag coefficient (CD,par) by obtaining agreement between the calculated minimum power (Vmin) and the observed minimum wingbeat frequency does not appear to be valid in this species, possibly due to upstroke pauses that occur at intermediate and high speeds, causing the apparent wingbeat frequency to be lower. These upstroke pauses represent flap-gliding, which is possibly a way of adjusting the force generated to the requirements at medium and high speeds, similar to the flap-bound mode of flight in other species. Body tilt angle, tail spread and angle of attack all increase with decreasing speed, thereby providing an additional lift surface and suggesting an important aerodynamic function for the tail at low speeds in forward flight. Results from this study indicate the high plasticity in the wingbeat kinematics and use of the tail that birds have available to them in order to adjust the lift and power output required for flight.

An optical tracking device recorded the three-dimensional paths of 11 dives by a 1.02 kg gyrfalcon, trained to dive to a falconer. The dives started at altitudes up to 500 m above the ground and were inclined at angles of 17-62 degrees from the horizontal. The falcon controlled its speed during the dives, rather than simply falling from the sky, and the dives had three phases. During the first (acceleration) phase, the falcon accelerated to speed limits between 52 and 58 m s-1 in the seven fastest dives, evidently with minimum drag, because its accelerations were close to those predicted from theory for minimum drag. The falcon then began a constant-speed phase by increasing drag by a factor of 1.3-4.8 while still 100-350 m above the ground in most dives. The constant-speed phase lasted no more than a few seconds, and the falcon then began a deceleration phase by increasing its drag further, this time by factors of 1.7-3. 2, and decelerating with a mean value of -0.95 times gravitational acceleration. During all three phases, the dive angle was nearly constant or increased during the deceleration phase, and the falcon made no changes in its body shape that were obvious through the tracking device telescope except to reduce its wing span as it accelerated. The falconer, however, was close to the falcon at the end of the dive and could see that, during the deceleration phase, the falcon held its wings in a cupped position, apparently with a high angle of attack and therefore high drag. At the end of the deceleration phase, the falcon dropped its legs, spread its toes and finally spread its wings as it approached the falconer. Although the speeds reported here are the fastest ever measured with known accuracy in animals, the falcon could theoretically have reached more than 70 m s-1 if it had continued to accelerate with minimum drag until close to the ground. Even at this speed, it would have had enough altitude to pull out of the dive before crashing into the ground. Several authors have estimated that diving falcons reach speeds of more than 70 m s-1, and wild falcons may reach such speeds when they make long, steep dives upon birds flying high in the air.

Twin non-parallel jet configurations occur in many practical devices like burners, combustion chambers, and also in the area of fluidics etc. Despite the importance of such configurations, studies on the interaction of twin non-parallel jets are very limited. The present work is an attempt to investigate the mixing of two axisymmetric jets obliquely oriented towards each other. Experimental studies were made on the interaction of twin intersecting axisymmetric jets issuing from two unventilated convergent nozzles. The nozzles of exit diameter (D) 10 mm were set on a common end wall with their axes intersecting each other at half angles (α3) of 0°, 5°, 10° and 15°. The centre-to-centre spacing (S) of the nozzles, non-dimensionalized, as S/D, was 3.1. The jet exit Mach number (Me) studied was 0.2. The results indicate that the near field characteristics are strongly influenced by α3. However, the potential core of the individual jets and the far field characteristics of the twin jet flow field, that is beyond downstream distances of 40 nozzle diameters, are not significantly influenced by α3. The cross-section of the jet just downstream of the combining point is approximately elliptic. The axis switching phenomenon normally associated with non-circular jets is observed in the jet flow field. The spread of the combined jet is more in the transverse direction than in the spanwise direction. Entrainment of the ambient fluid is found to be more in the case of twin parallel jets (α3 = 0°). The entrainment decreases with increasing α3. The self-preserving nature of the combined jet is almost independent of the initial geometric conditions. The combined jet is axisymmetric with regard to the normalized velocity and length scales.

The glue spreader of lithium manganese button cell is the necessary facility in the button cell industry. In the incipit , design the machinery and describe it simply. The focal point of this article is that design the hydraulic and air pressure system for the glue spreader of lithium manganese button cell and also do some experiments. And also get the relation curve between the rotate speed and the time when solenoid valve is working. At last get the angle of the jet flow. Finally, introduce the control system. It includes control system function of the procedures and so on. And also make the program function diagram to analyse the PLC control system.

Abstract: Based on the basic theory of fluid dynamics and Fluent software, numeric simulation of self-excited oscillating cavitation jet nozzle for cleaning was carried out. The flow field characteristics within tubular organ cavitation nozzle is studied. By numerical simulation, the exit velocity, velocity vector distribution, pressure inside the nozzle as well as static pressure distribution were obtained. The simulation results show that there is a maximum speed at cylindric section inside the cavitation nozzle. When water jet getting into the cylindric section of the cavitation nozzle, there is a significant zone with high negative pressure.Also there is a obvious zone with negative pressure at the outlet end. When the pressure is below the saturation vapor pressure of the liquid, cavitation bubbles occured. Therefore the cavitating water jet was generated. The simulation results also show that there is a higher negative pressure inside the nozzle region when the nozzle inlet diameter Ds = 6 mm, the diameter of the cavity D = 3 mm, the diameter of the cylindric section d = 1.8mm, the resonator length L = 6.2 mm, spread angleα= 60 °, the length of the cylindric segment s = 6 mm, Thererfore it is beneficial effect for the cavitation generating.

A study of plane, underexpanded, condensing vapor jets was undertaken using flash photography and a ventilated pressure probe. This study examined horizontal jets with much lower condensation driving potentials than have been previously studied. Photographic measurements of jet expansion angles, spread angles, cavity lengths, and cavity shapes were recorded and compared with numerical predictions using a parabolic, locally homogeneous flow model that had been modified to incorporate entrainment and condensation effects. When rendered dimensionless by the nozzle width rather than diameter, the plane condensation length agreed well with previously published round jet correlations for higher condensation driving potentials. At lower condensation driving potentials, the jets began to disperse, showing behavior similar to submerged air and energetic reacting vapor jets. Numerical predictions of condensation length were in good agreement over the entire range of measurement. Numerical predictions of vapor cavity shape were in reasonable agreement at higher condensation potentials but underpredicted the width of the vapor cavity at lower potentials. Pressure measurements showed the existence of periodic expansion/compression cells associated with underexpanded noncondensing gas jets. When these measurements were compared with similar measurements of air jets into quiescent water baths, the lengths of the initial steam vapor expansion/compression cells were substantially greater than those of the air jets, and the degree of pressure recovery over the cell length was substantially less.

SummaryWe assess the ability of neutron star binary coalescence to produce short gamma-ray bursts (GRBs). We find that the neutrino annihilation above the merged remnant will drive bipolar, relativistic jets along the initial binary rotation axis. This outflow can be collimated by the energetic, neutrino-driven baryonic wind that is blown off the remnant. Despite the narrow neutron star mass distribution the apparent luminosities will be spread over a broad range from ~ 1049 to ~ 1052erg s−1, typical jet opening half-angles are around 5 degrees. If the central core of the merger remnant does not collapse immediately convective dynamo action will set in and the available kinetic energy can be transformed into magnetic fields in excess of 1017 G. The corresponding spin-down time scale is ~ 0.2 s, just about the duration of a short GRB.

Context. Very long baseline interferometry (VLBI) observations at 86 GHz (wavelength, λ = 3 mm) reach a resolution of about 50 μas, probing the collimation and acceleration regions of relativistic outflows in active galactic nuclei (AGN). The physical conditions in these regions can be studied by performing 86 GHz VLBI surveys of representative samples of compact extragalactic radio sources. Aims. To extend the statistical studies of compact extragalactic jets, a large global 86 GHz VLBI survey of 162 compact radio sources was conducted in 2010–2011 using the Global Millimeter VLBI Array (GMVA). Methods. The survey observations were made in a snapshot mode, with up to five scans per target spread over a range of hour angles in order to optimize the visibility coverage. The survey data attained a typical baseline sensitivity of 0.1 Jy and a typical image sensitivity of 5 mJy beam−1, providing successful detections and images for all of the survey targets. For 138 objects, the survey provides the first ever VLBI images made at 86 GHz. Gaussian model fitting of the visibility data was applied to represent the structure of the observed sources and to estimate the flux densities and sizes of distinct emitting regions (components) in their jets. These estimates were used for calculating the brightness temperature (Tb) at the jet base (core) and in one or more moving regions (jet components) downstream from the core. These model-fit-based estimates of Tb were compared to the estimates of brightness temperature limits made directly from the visibility data, demonstrating a good agreement between the two methods. Results. The apparent brightness temperature estimates for the jet cores in our sample range from 2.5 × 109 K to 1.3 × 1012 K, with the mean value of 1.8 × 1011 K. The apparent brightness temperature estimates for the inner jet components in our sample range from 7.0 × 107 K to 4.0 × 1011 K. A simple population model with a single intrinsic value of brightness temperature, T0, is applied to reproduce the observed distribution. It yields T0 = (3.77−0.14+0.10) × 1011 K for the jet cores, implying that the inverse Compton losses dominate the emission. In the nearest jet components, T0 = (1.42−0.19+0.16) × 1011 K is found, which is slightly higher than the equipartition limit of ∼5 × 1010 K expected for these jet regions. For objects with sufficient structural detail detected, the adiabatic energy losses are shown to dominate the observed changes of brightness temperature along the jet.

In the forming section of a paper machine, pulp is spread over a moving fabric and water is drained through the fabric. The fibers left behind form a wet sheet. The mechanical dewatering that begins in the forming section is important to the final paper quality because any non-uniformities arising in this section cannot be corrected later in the paper machine. Therefore, understanding the flow field through the forming section provides insight into the finished paper. We analyzed the effect of the machine-side filaments of the fabric on the flow field upstream of the paper-side filaments. The resistance of a multilayer fabric was found to be nearly equal to the sum of the resistances of each layer considered in isolation. For the particular fabric, the machine-side layer produced up to a 10% effect on the velocity above the paper-side layer. For the effect of jet-to-wire speed ratio on the flow, an angled approach flow to the fabric produced very little change in the average flow perpendicular to the fabric (i.e., little change in fabric permeability). However, it has a marked effect on the machine-direction shear stress in the vicinity of the paper-side filaments. This shear stress drives the fiber orientation characteristics of so-called rush or drag jet impingement.

We consider the steady flow near a free surface at intermediate to high Reynolds numbers, both experimentally and theoretically. In our experiment, an axisymmetric capillary meniscus is suspended from a cylindrical tube, held slightly above a horizontal water surface. A flow of dyed water is released through the tube into the reservoir, and flow lines are thus recorded. At low Reynolds numbers, flow lines follow the free surface, and injected water spreads horizontally inside the container. Increasing the Reynolds number, the injected fluid penetrates to a certain distance into the bath, but ultimately follows the free surface. Above a critical Reynolds number of approximately 60, the flow separates from the free surface in the meniscus region and a jet projects vertically into the bath. We find no indication that the flow reattaches at higher Reynolds numbers, nor are our findings sensitive to surface contamination. We show theoretically and confirm experimentally that the separating streamline forms a right angle with the free surface.

To investigate how birds that differ in morphology change their wing and body movements while flying at a range of speeds, we analyzed high-speed (60 Hz) video tapes of black-billed magpies (Pica pica) flying at speeds of 4-14 m s-1 and pigeons (Columba livia) flying at 6-20 m s-1 in a wind-tunnel. Pigeons had higher wing loading and higher-aspect-ratio wings compared with magpies. Both species alternated phases of steady-speed flight with phases of acceleration and deceleration, particularly at intermediate flight speeds. The birds modulated their wingbeat kinematics among these phases and frequently exhibited non-flapping phases while decelerating. Such modulation in kinematics during forward flight is typical of magpies but not of pigeons in the wild. The behavior of the pigeons may have been a response to the reduced power costs for flight in the closed wind-tunnel relative to those for free flight at similar speeds. During steady-speed flight, wingbeat frequency did not change appreciably with increasing flight speed. Body angle relative to the horizontal, the stroke-plane angles of the wingtip and wrist relative to the horizontal and the angle describing tail spread at mid-downstroke all decreased with increasing flight speed, thereby illustrating a shift in the dominant function of wing flapping from weight support at slow speeds to positive thrust at fast speeds. Using wingbeat kinematics to infer lift production, it appeared that magpies used a vortex-ring gait during steady-speed flight at all speeds whereas pigeons used a vortex-ring gait at 6 and 8 m s-1, a transitional vortex-ring gait at 10 m s-1, and a continuous-vortex gait at faster speeds. Both species used a vortex-ring gait for acceleration and a continuous-vortex gait or a non-flapping phase for deceleration during flight at intermediate wind-tunnel speeds. Pigeons progressively flexed their wings during glides as flight speed increased but never performed bounds. Wingspan during glides in magpies did not vary with flight speed, but the percentage of bounds among non-flapping intervals increased with speed from 10 to 14 m s-1. The use of non-flapping wing postures seemed to be related to the gaits used during flapping and to the aspect ratio of the wings. We develop an 'adverse-scaling' hypothesis in which it is proposed that the ability to reduce metabolic and mechanical power output using flap-bounding flight at fast flight speeds is scaled negatively with body mass. This represents an alternative to the 'fixed-gear' hypothesis previously suggested by other authors to explain the use of intermittent flight in birds. Future comparative studies in the field would be worthwhile, especially if instantaneous flight speeds and within-wingbeat kinematics were documented; new studies in the laboratory should involve simultaneous recording of wing kinematics and aerodynamic forces on the wing.

The aim of this paper is to reassess John Steinbeck’s presence and significance within American modernism by advancing a myth-critical reading of his early novel “To a God Unknown” (1933). Considering the interplay between this novel and the precedent literary tradition and other contextual aspects that might have influenced Steinbeck’s text, this study explores Steinbeck’s often disregarded novel as an eloquent demonstration of the malleability of myths characteristic of Anglo-American modernism. Taking myth-ritualism—the most prominent approach to myth at the time—as a critical prism to reappraise Steinbeck’s own reshaping of modernist aesthetics, this article examines recurrent frustrated and misguided ritual patterns along with the rewriting of flouted mythical motifs as a series of aesthetic choices that give shape and meaning to a state of stagnation common to the post-war American literary landscapes, but now exacerbated as it has finally spread, as a plague of perverse remythologization, to the Eden of the West.

We investigate source mechanisms for subsonic jet noise using experimentally obtained datasets of high-Reynolds-number Mach 0.4 and 0.6 turbulent jets. The focus is on the axisymmetric mode which dominates downstream sound radiation for low polar angles and the frequency range at which peak noise occurs. A linearized Euler equation (LEE) solver with an inflow boundary condition is used to generate single-frequency hydrodynamic instability waves, and the resulting near-field fluctuations and far-field acoustics are compared with those from experiments and linear parabolized stability equation (LPSE) computations. It is found that the near-field velocity fluctuations closely agree with experiments and LPSE computations up to the end of the potential core, downstream of which deviations occur, but the LEE results match experiments better than the LPSE results. Both the near-field wavepackets and the sound field are observed directly from LEE computations, but the far-field sound pressure levels (SPLs) obtained are more than an order of magnitude lower than experimental values despite close statistical agreement of the near hydrodynamic field up to the potential core region. We explore the possibility that this discrepancy is due to the mismatch between the decay of two-point coherence with increasing distance in experimental flow fluctuations and the perfect coherence in linear models. To match the near-field coherence, experimentally obtained coherence profiles are imposed on the two-point cross-spectral density (CSD) at cylindrical and conical surfaces that enclose near-field structures generated with LEEs. The surface pressure is propagated to the far field using boundary value formulations based on the linear wave equation. Coherence matching yields far-field SPLs which show improved agreement with experimental results, indicating that coherence decay is the main missing component in linear models. The CSD on the enclosing surfaces reveals that the application of a decaying coherence profile spreads the hydrodynamic component of the linear wavepacket source on to acoustic wavenumbers, resulting in a more efficient acoustic source.

Historically, high probe current in small probes has been the principal virtue of the field emission TEM. Analytical performance is greatly enhanced[1] and fine probe mapping an important analytical tool for trace element segregation and very fine scale high resolution chemical imaging. Less appreciated is the enhanced high resolution capability due to the small energy spread of the electron source and higher coherency due to reduced primary and virtual source size. The envelope function of the phase contrast transfer function (PCTF) is drastically improved reducing image blurring due to both chromatic aberration and specimen illumination angle. This is especially true for the high spatial frequencies beyond the first zero. Intensities sufficient for image formation can be obtained from these higher frequency regions. Since the PCTF does not change its form, photographing images at the Scherzer condition will yield higher resolution with higher coherency, however, the transfer of the specimen potential corresponding to contrast enhanced regions is in the oscillations form beyond the first zero. Changes in the defocus will lead to changes in transferred frequencies beyond the first zero and possible extinctions of otherwise transferred information since the oscillations will pass through zero contrast. Interpretation of images under these conditions will, therefore, require accurate measurement of the optical parameters of the microscope and especially accurate measurements of the defocus conditions. It is also important to calculate images under these conditions for comparison with measured images which give the insurance of defocus conditions supposed to be presented.

Differential phase contrast Lorentz. microscopy has been shown to be a powerful technique for studying submicron magnetisation distributions in thin magnetic films. However, the technique has not found wide spread use, perhaps because it is thought to require either a dedicated STEM with a field emission gun, or extensive modifications to the electron optics of a conventional TEM. In this work we have demonstrated that DPC can be implemented on a conventional TEM, in our case a JEOL JEM 2000FX, without recourse to modifications ofthe electron optics ofthe microscope. Some of the controls of the microscope have been modified, but this was for convenience rather than necessity and in no way affects the normal operation ofthe microscope.Figure I illustrates the principle behind DPC. A focused electron probe, of half angle α is scanned across the sample and at each point in the scan, the denection (β1) due to the sample is measured by means of a quadrant detector as follows. Any deflection of the beam can he split into an x-component and a y-component.

Electrohydrodynamic jet (e-jet) printing is a microscale additive manufacturing technique used to print microscale constructs, including next-generation biological and optical sensors. Despite the many advantages to e-jet over competing microscale additive manufacturing techniques, there do not exist validated models of build material drop formation in e-jet, relegating process design and control to be heuristic and ad hoc. This work provides a model to map deposited drop volume to final spread topography and validates this model over the drop volume range of 0.68–13.4 pL. The model couples a spherical cap volume conservation law to a molecular kinetic relationship for contact line velocity and assumes an initial contact angle of 180 deg to predict the drop shape dynamics of dynamic contact angle and dynamic base radius. For validation, the spreading of e-jet-printed drops of a viscous adhesive is captured by high-speed microscopy. Our model is validated to have a relative error less than 3% in dynamic contact angle and 1% in dynamic base radius.

The film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by pressure sensitive paint (PSP) under different density ratios. Several hole geometries are studied, including streamwise cylindrical holes, compound-angled cylindrical holes, streamwise fan-shape holes, compound-angled fan-shape holes, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35 deg. The compound angle (β) is 45 deg. The fan-shape holes have a 10 deg expansion in the spanwise direction. For a fair comparison, the pitch is kept as 4d for the cylindrical and the fan-shape holes, and 8d for the DJFC holes. The uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. The effects of density ratios (DR = 1.0, 1.5 and 2.5) on the film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. The results show that at higher density ratios, the lateral spread of the discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, while the DJFC holes is more advantageous in film-cooling effectiveness. Mostly, a higher lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of the density ratio on the lateral-uniformity are not monotonic in some cases. Utilizing the compound angle configuration leads to an increased lateral-uniformity due to a stronger spanwise motion of the jet. Generally, with a higher blowing ratio, the lateral-uniformity of the discrete-hole geometries decreases due to narrower traces, while that of the DJFC holes increases due to a stronger spanwise movement.

The interaction between a mildly underexpanded supersonic jet and a single cylinder was studied experimentally at laboratory scale by using the schlieren technique coupled with high-speed photography and pitot pressure measurements. This study was motivated by the need to optimize sootblowing operation in kraft recovery boilers. The effects of the transverse distance between the jet and cylinder centerlines (eccentricity), nozzle–cylinder distance, and cylinder size on jet–cylinder interaction were determined. Results show that upon impingement on a cylinder, a supersonic jet deflects at an angle and creates a weaker supersonic jet that we refer to as a “secondary” jet. The angle and strength of the deflected or secondary jet depend on the eccentricity between the primary jet and cylinder centerlines. When a jet impinges on a cylinder of diameter comparable to that of the jet or smaller, secondary jets form not only when the cylinder is placed close to the nozzle (in the stronger portion of the jet) but also when the cylinder is placed far away (in the jet's weaker portion; up to 20–24 nozzle exit diameters in the present study). Changing the eccentricity slightly results in a significant change in the secondary jet characteristics. For a cylinder much larger than the jet, secondary jets do not form at zero eccentricity (head-on impingement); the eccentricity at which they begin to form increases with the cylinder size. A study of the secondary jets shows that they spread out much more than the primary jet and are sheet- or fan-like with an oblong, oval cross section. The centerline pitot pressure of the secondary jets remains as high as the primary jet for a considerable distance from the tube only during weak interaction between the primary jet and the cylinder (i.e., during strongly eccentric/off-centerd impingement). As the interaction between the primary jet and the cylinder intensifies at lower eccentricities, the maximum centerline pitot pressure of the secondary jet decreases, and the pitot pressure decreases more quickly with distance from the tube.

Shaped film cooling holes are a well-established cooling technique used in gas turbines to keep component metal temperatures in an acceptable range. One of the goals of film cooling is to reduce the driving temperature for convection at the wall, the success of which is generally represented by the film cooling adiabatic effectiveness. However, the introduction of a film cooling jet-in-crossflow, especially if it is oriented at a compound angle, can augment the convective heat transfer coefficient and dominate the flowfield. This work aims to understand the effect that a compound angle has on the flowfield and adiabatic effectiveness of a shaped film cooling hole. Five orientations of the public 7–7–7 shaped film cooling hole were tested, from a streamwise-oriented hole (0 deg compound angle) to a 60 deg compound angle hole, in increments of 15 deg. Additionally, two pitchwise spacings of P/D = 3 and 6 were tested to examine the effect of hole-to-hole interaction. All cases were tested at a density ratio of 1.2 and blowing ratios ranging from 1.0 to 4.0. The experimental results show that increasing compound angle leads to increased lateral spread of coolant and enables higher laterally averaged effectiveness at high-blowing ratios. A smaller pitchwise spacing leads to more complete coverage of the endwall and has higher laterally averaged effectiveness even when normalized by coverage ratio, suggesting that hole to hole interaction is important for compound angled holes. Steady Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) was not able to capture the exact effectiveness levels, but did predict many of the observed trends. The lateral motion of the coolant jet was also quantified, both from the experimental data and the CFD prediction, and as expected, holes with a higher compound angle and higher blowing ratio have greater lateral motion, which generally also promotes hole-to-hole interaction.

Abstract Three-dimensional Reynolds-averaged Navier–Stokes equations with shear stress transport turbulence model are used to analyze the film cooling effectiveness on a flat plate having single row of film hole involving cylindrical hole (CH) and laidback hole (LBH). The CH and LBH are inclined at 35 deg to the surface with a compound angle (β) orientation ranging from favorable to adverse inclination (i.e., β = 0–180 deg) and examined at high and low blowing ratios (M = 1.25 and 0.60). CH with an adverse compound angle of 135 deg gives the highest area-averaged film cooling effectiveness in comparison with LBH configuration. Also, CH β = 135 deg film hole shows a higher lateral coolant spread. Later, double jet film cooling (DJFC) concept is studied for this CH. In all the cases, the first hole compound angle is fixed as 135 deg, and the second hole angle is varied from 135 deg to 315 deg. At high blowing ratio, the dual jet cylindrical hole (DJCH) with β = 135 deg, 315 deg gives a higher area-averaged film cooling effectiveness by around 66.50% compared to baseline CH β = 0 deg. On comparing all CH, LBH, and DJCH cases, the highest area-averaged film cooling effectiveness is obtained by CH configuration with β = 135 deg. Hence, the CH with its adverse compound angle (β = 135 deg) orientation could be an appropriate film cooling configuration for gas turbine blade cooling.

Abstract This study was conducted to quantify in a controlled manner the effect of oscillator scale and working fluid on oscillator performance. The performance parameters of interest include the oscillation frequency and oscillation spread angle. Three scale models were manufactured with model attributes identical except for scale with models at two times and three times a baseline scale. Four working fluids were tested including helium, ethylene, carbon dioxide, and propane to generate a range of densities and viscosities. The frequency and oscillation angle measurements were obtained using high-speed video recordings of visible schlieren imagery. Trends in frequency were observed and quantified for each oscillator scale and working gas as a function of mass flowrate. This paper shows that these values could all be nondimensionalized with the data collapsing to a single Strouhal number between 0.015 and 0.018 depending on surface roughness, independent of the Reynolds number. This result expands on the authors' previously published work and confirms the previous finding that reveals the geometry and fluid properties also scale and collapse.

Abstract We explore how to improve the hybrid model description of the particles originating from the wake that a jet produced in a heavy ion collision leaves in the droplet of quark-gluon plasma (QGP) through which it propagates, using linearized hydrodynamics on a background Bjorken flow. Jet energy and momentum loss described by the hybrid model become currents sourcing linearized hydrodynamics. By solving the linearized hydrodynamic equations numerically, we investigate the development of the wake in the dynamically evolving droplet of QGP, study the effect of viscosity, scrutinize energy-momentum conservation, and check the validity of the linear approximation. We find that linearized hydrodynamics works better in the viscous case because diffusive modes damp the energy-momentum perturbation produced by the jet. We calculate the distribution of particles produced from the jet wake by using the Cooper-Frye prescription and find that both the transverse momentum spectrum and the distribution of particles in azimuthal angle are similar in shape in linearized hydrodynamics and in the hybrid model. Their normalizations are different because the momentum-rapidity distribution in the linearized hydrodynamics analysis is more spread out, due to sound modes. Since the Bjorken flow has no transverse expansion, we explore the effect of transverse flow by using local boosts to add it into the Cooper-Frye formula. After including the effects of transverse flow in this way, the transverse momentum spectrum becomes harder: more particles with transverse momenta bigger than 2 GeV are produced than in the hybrid model. Although we defer implementing this analysis in a jet Monte Carlo, as would be needed to make quantitative comparisons to data, we gain a qualitative sense of how the jet wake may modify jet observables by computing proxies for two example observables: the lost energy recovered in a cone of varying open angle, and the fragmentation function. We find that linearized hydrodynamics with transverse flow effects added improves the description of the jet wake in the hybrid model in just the way that comparison to data indicates is needed. Our study illuminates a path to improving the description of the wake in the hybrid model, highlighting the need to take into account the effects of both transverse flow and the broadening of the energy-momentum perturbation in spacetime rapidity on particle production.

This paper describes the experimental results of a new film cooling method that utilizes swirling coolant flow through circular and shaped film cooling holes. The experiments were conducted by using a scale-up model of a film-cooling hole installed on the bottom surface of a low-speed wind tunnel. Swirling motion of the film coolant was induced inside a hexagonal plenum using two diagonal impingement jets, which were inclined at an angle of α toward the vertical direction and installed in staggered positions. These two impingement jets generated a swirling flow inside the plenum, which entered the film-cooling hole and maintained its angular momentum until exiting the film-cooling hole. The slant angle of the impingement jets was changed to α = 0 deg, 10 deg, 20 deg, and 30 deg in the wind tunnel tests. The film cooling effectiveness on a flat wall was measured by a pressure sensitive paint (PSP) technique. In addition, the spatial distributions of the nondimensional concentration (or temperature) and flow field were measured by laser-induced fluorescence (LIF) and particle image velocimetry (PIV), respectively. In the case of a circular film-cooling hole, the penetration of the coolant jet into the mainstream was suppressed by the swirling motion of the coolant. As a result, although the coolant jet was deflected in the pitch direction, the film cooling effectiveness on the wall maintained a higher value behind the cooling hole over a long range. Additionally, the kidney vortex structure disappeared. For the shaped cooling hole, the coolant jet spread wider in the spanwise direction downstream. Thus, the pitch-averaged film cooling effectiveness downstream was 50% higher than that in the nonswirling case.

This paper presents a method to improve the film-cooling effectiveness of cylindrical holes. A short crescent-shaped block is placed at the downstream of a cylindrical cooling hole. The block shape is defined by a number of geometric parameters including block height, length and width, etc. The single row hole on a flat plate with inclination angle of 30 deg, pitch ratio of 3, and length-diameter ratio of 6.25 was chosen as the baseline test case. Film-cooling effectiveness for the cylindrical hole with or without the downstream short crescent-shaped block was measured by using the pressure sensitive paint (PSP) technique. The density ratio of coolant (argon) to mainstream air is 1.38. The blowing ratios vary from 0.5 to 1.25. The results showed that the lateral averaged cooling effectiveness is increased remarkably when the downstream block is present. The downstream short block allows the main body of the coolant jet to pass over the block top and to form a new down-wash vortex pair, which increases the coolant spread in the lateral direction. The effects of each geometrical parameter of the block on the film-cooling effectiveness were studied in detail.

Film cooling in turbine blades involves injecting cold air through small holes over the surface of the blade to thermally protect it against the incoming hot freestream. Compound angled film cooling, in which the injected jet is angled laterally with respect to the streamwise flow direction, is used in industrial designs owing to their lower cost of manufacture compared with shaped geometries but a high coolant spread. The current study incorporates flow structure measurements of film cooling injection flows inclined at 30 deg to a flat surface with lateral angles of 15 deg, 60 deg, and 90 deg to the freestream. Blowing ratios of 1–2 and density ratios of 1–1.5 are studied. Three dimensional velocity measurements are carried out through high resolution stereoscopic particle image velocimetry. It is observed that the typical counter-rotating vortex pair structure associated with streamwise coolant injection is replaced with a single large vortex, which causes a more lateral spread of the coolant. Infrared thermography measurements are made for the same operating points using the super position principle, which allows calculation of adiabatic effectiveness and heat transfer coefficient. The adiabatic effectiveness is high at low blowing ratios for compound angled injection due to greater proximity of the coolant jet to the wall. At higher blowing ratios, the detrimental effects on effectiveness due to jet lift-off are counteracted by the greater coolant spread due to asymmetric primary vorticity. The heat transfer coefficient is also enhanced especially in the downstream region for high compound angles. The average heat transfer coefficient due to very large compound angles is not very sensitive to changing momentum flux ratios.

Heat extraction and drop impact regimes occurring when a local portion of a horizontal flat-fan air mist impinges the active surface of a Pt disk hold at Tw from ∼60 to 1200 °C are investigated. Boiling curves comprise single-phase, nucleate boiling (NB), transition boiling (TB), and film boiling (FB). Mists are generated under wide ranges of water and air flow rates, and the disk is placed at center and off-center positions along the mist footprint major axis. Conditions generate a wide spectrum of water impact flux, w, droplet diameter, dd, droplet velocity, uzs, and impingement angle. Heat flux extracted, −q, along each boiling regime correlates very well with expressions involving Reynolds, Weber, and Jakob numbers evaluated in terms of local average characteristics of free nonimpinging mists—w, volume mean diameter, d30, normal volume weighted mean velocity, uz,v—and Tw; close estimation indicates that hydrodynamic and thermal forces are well accounted. During arrival of sparse parcels visualization of mist–wall interactions, using a high speed camera aided by laser illumination, allows determination of the predominance area diagram of droplet impact regimes in terms of normal impinging Weber number, Wez, and Tw. The regimes include stick, rebound, spread, and splash; the last subclassified as fine-, crown- and jet-atomization. Arrival of parcels in close succession is ubiquitous causing rapid surface flooding and leading to formation of discontinuous well agitated thick liquid films, which interacts longer with the surface than drops in sparse parcels, acting as heat sinks for longer periods of time.

California sea lions (Zalophus californianus) are a highly maneuverable species of marine mammal. During uninterrupted, rectilinear swimming, sea lions oscillate their foreflippers to propel themselves forward without aid from the collapsed hindflippers, which are passively trailed. During maneuvers such as turning and leaping (porpoising), the hindflippers are spread into a delta-wing configuration. There is little information defining the role of otarrid hindflippers as aquatic control surfaces. To examine Z. californianus hindflippers during maneuvering, trained sea lions were video recorded underwater through viewing windows performing porpoising behaviors and banking turns. Porpoising by a trained sea lion was compared to sea lions executing the maneuver in the wild. Anatomical points of reference (ankle and hindflipper tip) were digitized from videos to analyze various performance metrics and define the use of the hindflippers. During a porpoising bout, the hindflippers were considered to generate lift when surfacing with a mean angle of attack of 14.6±6.3°. However, while performing banked 180o turns, the mean angle of attack of the hindflippers was 28.3±7.3°, and greater by another 8-12° for the maximum 20% of cases. The delta-wing morphology of the hindflippers may be advantageous at high angles of attack to prevent stalling during high-performance maneuvers. Lift generated by the delta-shaped hindflippers, in concert with their position far from the center of gravity, would make these appendages effective aquatic control surfaces for executing rapid turning maneuvers.

Abstract The fundamental operation in binder jet three-dimensional printing is the deposition of liquid binder into a powder layer to selectively bond particles together. Upon droplet impact, the binder spreads into the powder bed forming a bound network of wetted particles called a primitive. A computational fluid dynamics framework is proposed to directly simulate the capillary and hydrodynamic effects of the interfacial flow that is responsible for primitive formation. The computational model uses the volume-of-fluid method for capturing dynamic binder-air interfaces, and the immersed boundary method is adopted to include particle geometries on numerical Cartesian grids. Three-phase contact angles are prescribed through an interface extension algorithm. Binder droplet impact on powder beds of varying contact angle are simulated. Furthermore, the numerical model is used to simulate liquid bridges connecting binary and ternary particle systems, and the resulting capillary and hydrodynamic forces are validated by comparison with published experimental and theoretical model results.

Abstract This paper presents the experimental analysis of the impact of swirl number of cross-flowing air stream on liquid jet spray trajectory at a fixed air flow velocity of 42 m/s with the corresponding Mach number of 0.12. The experiments were conducted for 4 different swirl numbers (0, 0.2, 0.42 and 0.73) using swirl vanes at air inlet having angles of 0°, 15°, 30° and 45° respectively. Liquid to air momentum flux ratio (q) was varied from 5 to 25. High speed (@ 500 fps) images of the spray were captured and those images were processed using MATLAB to obtain the path of the spray at various momentum flux ratios. The results show interesting trends for the spray trajectory and the jet spread in swirling air flow. High swirling flows not only lead to spray with lower radial penetration due to sharp bending and disintegration of liquid jet, but also result in spray with high jet spread and spray area. Based on the results, correlations for the spray path have been proposed which incorporates the effects of the swirl number of the air flow.

Improving engine performance is a constant challenge and various methodologies have been adopted by researcher’s world over. In this work, the dispersion characteristics of a rotating injector is studied by varying the umbrella angle (UA) followed by its combustion characteristics and comparing it to a static 3 – hole injector. The present numerical study is bench marked with the experimental data obtained from open literature for a 2 – hole injector with various umbrella angles. The volume fraction of the dispersed fuel along with its spray structure in relation to spray width is compared. This is done by processing the numerical contour plot using LabView image processing utility with appropriate calibration. From this study the 130 degree UA injector configuration was found to be effective when compared with 70. The combustion characteristics is now studied for this injector. It is found that the rotating injector has better dispersion and lowers NOx by 14 % when compared to a static injector with a very marginal loss in thermal efficiency. The rotary system has a lower heat release but a wider spread in comparison to a static case. This helps in marginally reducing the in-cylinder temperature and pressure lower NOx.

Depicted are sequences of water drop impacts on copper, taken at 16,000 fps. The copper is treated with a heated alkali solution, resulting in a highly wetting, nanoscale structured, cupric oxide layer with a static contact angle approaching 0° with water. In the top series an 11.5 µl water droplet impacts this surface from 60 mm. The interfacial forces are large compared with the inertia; the low advancing contact angle of the expanding front continues to pull the droplet outward and absorbs the droplet without any rebound. The droplet spreads to cover the entire 0.5x0.5 in2 surface in less than 500 ms. After the surface energy of the oxide layer is reduced with silane, this surface becomes highly non-wetting with a static contact angle of ~160° and a hysteresis <5°. The lower sequence shows the 11.5 µl water droplet dropped from the same height. The large advancing contact angle creates an inverted wedge at the triple line, and the advancing front quickly reaches a maximum diameter at 3 ms and begins to recede inward while the top of the droplet is still moving downward, creating a donut shape. The receding front collides at the center forcing a jet of liquid up and out. This jet pulls the remainder of the liquid upward at a decreasing velocity, relative to the head. This is apparent as the jet splits into secondary droplets at 16ms (which moves out of frame at 18 ms) and again at 22 ms, referred to as S-1 and S-2, respectively. As the S-2 splits off, surface tension force cause it to slow at 25 ms, while the parent droplet moves up to collide with, and impart momentum to S-2. They remain detached; S-2 moves out of view, the parent falls. This bouncing behavior continues until the energy is dissipated and the droplets come to rest. This can be seen as the parent drop rebounds again at 100ms, S-2 at 130 ms and S-1 in the final frame, forming a tertiary droplet. These surfaces are being studied for their effects on two phase heat transfer.

Abstract Using hand-collected data, we show that coinvestment is widespread in the angel investment market, even among seed-stage startups. Individual angels with demonstrated seed-stage success experience an increase in the quantity, quality, and geographic and industry spread of their coinvestment connections relative to unsuccessful peers and are rewarded with more deal flow. These results are stronger for less-established angels and for angels whose successes are more indicative of their ability. Success also begets more success: the portfolio companies of successful angels are more likely to receive follow-on financing, especially from VC firms. Our results highlight how angels grow their coinvestment networks. (JEL G24, L14, L26, M13). Received June 8, 2020; editorial decision June 21, 2021 by Editor Isil Erel. Authors have furnished an Internet Appendix, which is available on the Oxford University Press Web site next to the link to the final published paper online.

A late-injection, high exhaust-gas recirculation rate, low-temperature combustion strategy is investigated in a heavy-duty diesel engine using a suite of optical diagnostics: chemiluminescence for visualization of ignition and combustion, laser Mie scattering for liquid-fuel imaging, planar laser-induced fluorescence (PLIF) for both OH and vapor-fuel imagings, and laser-induced incandescence for soot imaging. Fuel is injected at top dead center when the in-cylinder gases are hot and dense. Consequently, the maximum liquid-fuel penetration is 27 mm, which is short enough to avoid wall impingement. The cool flame starts 4.5 crank angle degrees (CAD) after the start of injection (ASI), midway between the injector and bowl rim, and likely helps fuel to vaporize. Within a few CAD, the cool-flame combustion reaches the bowl rim. A large premixed combustion occurs near 9 CAD ASI, close to the bowl rim. Soot is visible shortly afterward, along the walls, typically between two adjacent jets. OH PLIF indicates that premixed combustion first occurs within the jet and then spreads along the bowl rim in a thin layer, surrounding soot pockets at the start of the mixing-controlled combustion phase near 17 CAD ASI. During the mixing-controlled phase, soot is not fully oxidized and is still present near the bowl rim late in the cycle. At the end of combustion near 27 CAD ASI, averaged PLIF images indicate two separate zones. OH PLIF appears near the bowl rim, while broadband PLIF persists late in the cycle near the injector. The most likely source of broadband PLIF is unburned fuel, which indicates that the near-injector region is a potential source of unburned hydrocarbons.

0. IntroductionIf we follow the line of much literature surrounding airports and urban mobility, the emphasis often falls on the fact that these spaces are designed to handle the mega-scale and super-human pace of mass transit. Airports have rightly been associated with velocity, as zones of rapid movement managed by enormous processing systems that guide bodies and things in transit (Pascoe; Pearman; Koolhaas; Gordon; Fuller & Harley). Yet this emphasis tends to ignore the spectrum of tempos and flows that are at play in airport terminals — from stillness to the much exalted hyper-rapidity of mobilized publics in the go-go world of commercial aviation.In this photo essay I'd like to pull a different thread and ask whether it's possible to think of aeromobility in terms of “uneven, differential mobility” (Bissell 280). What would it mean to consider waiting and stillness as forms of bodily engagement operating over a number of different scales and temporalities of movement and anticipation, without privileging speed over stillness? Instead of thinking mobility and stillness as diametrically opposed, can we instead conceive of them as occupying a number of different spatio-temporal registers in a dynamic range of mobility? The following is a provisional "visual ethnography" constructed from photographs of air terminal light boxes I have taken over the last five years (in Amsterdam, London, Chicago, Frankfurt, and Miami). Arranged into a "taxonomy of differentiality", each of these images comes from a slightly different angle, mode or directionality. Each view of these still images displayed in billboard-scale light-emitting devices suggests that there are multiple dimensions of visuality and bodily experience at play in these image-objects. The airport is characterized by an abundance of what appears to be empty space. This may be due to the sheer scale of mass transport, but it also arises from a system of active and non-active zones located throughout contemporary terminals. This photo series emphasises the "emptiness" of these overlooked left-over spaces that result from demands of circulation and construction.1. We Move the WorldTo many travellers, airport gate lounges and their surrounding facilities are loaded with a variety of contradictory associations and affects. Their open warehouse banality and hard industrial sterility tune our bodies to the vast technical and commercial systems that are imbricated through almost every aspect of contemporary everyday life.Here at the departure gate the traveller's body comes to a moment's rest. They are granted a short respite from the anxious routines of check in, body scans, security, information processing, passport scanning, itineraries, boarding procedures and wayfaring the terminal. The landside processing system deposits them at this penultimate point before final propulsion into the invisible airways that pipe them into their destination. We hear the broadcasting of boarding times, check-in times, name's of people that break them away from stillness, forcing people to move, to re-arrange themselves, or to hurry up. Along the way the passenger encounters a variety of techno-spatial experiences that sit at odds with the overriding discourse of velocity, speed and efficiency that lie at the centre of our social understanding of air travel. The airline's phantasmagorical projections of itself as guarantor and enabler of mass mobilities coincides uncomfortably with the passenger's own wish-fulfilment of escape and freedom.In this we can agree with the designer Bruce Mau when he suggests that these projection systems, comprised of "openings of every sort — in schedules, in urban space, on clothes, in events, on objects, in sightlines — are all inscribed with the logic of the market” (Mau 7). The advertising slogans and images everywhere communicate the dual concept that the aviation industry can deliver the world to us on time while simultaneously porting us to any part of the world still willing to accept Diners, VISA or American Express. At each point along the way these openings exhort us to stop, to wait in line, to sit still or to be patient. The weird geographies depicted by the light boxes appear like interpenetrating holes in space and time. These travel portals are strangely still, and only activated by the impending promise of movement.Be still and relax. Your destination is on its way. 2. Attentive AttentionAlongside the panoramic widescreen windows that frame the choreography of the tarmac and flight paths outside, appear luminous advertising light boxes. Snapped tightly to grid and locked into strategic sightlines and thoroughfares, these wall pieces are filled with a rotating menu of contemporary airport haiku and ersatz Swiss graphic design.Mechanically conditioned air pumped out of massive tubes creates the atmosphere for a very particular amalgam of daylight, tungsten, and fluorescent light waves. Low-oxygen-emitting indoor plants are no match for the diesel-powered plant rooms that maintain the constant flow of air to every nook and cranny of this massive processing machine. As Rem Koolhaas puts it, "air conditioning has launched the endless building. If architecture separates buildings, air conditioning unites them" (Koolhaas). In Koolhaas's lingo, these are complex "junkspaces" unifying, colliding and coalescing a number of different circulatory systems, temporalities and mobilities.Gillian Fuller reminds us there is a lot of stopping and going and stopping in the global circulatory system typified by air-terminal-space.From the packing of clothes in fixed containers to strapping your belt – tight and low – stillness and all its requisite activities, technologies and behaviours are fundamental to the ‘flow’ architectures that organize the motion of the globalizing multitudes of today (Fuller, "Store" 63). It is precisely this functional stillness organised around the protocols of store and forward that typifies digital systems, the packet switching of network cultures and the junkspace of airports alike.In these zones of transparency where everything is on view, the illuminated windows so proudly brought to us by J C Decaux flash forward to some idealized moment in the future. In this anticipatory moment, the passenger's every fantasy of in-flight service is attended to. The ultimate in attentiveness (think dimmed lights, soft pillows and comfy blankets), this still image is captured from an improbable future suspended behind the plywood and steel seating available in the moment —more reminiscent of park benches in public parks than the silver-service imagined for the discerning traveller.3. We Know ChicagoSelf-motion is itself a demonstration against the earth-binding weight of gravity. If we climb or fly, our defiance is greater (Appleyard 180).The commercial universe of phones, cameras, computer network software, financial instruments, and an array of fancy new gadgets floating in the middle of semi-forgotten transit spaces constitutes a singular interconnected commercial organism. The immense singularity of these claims to knowledge and power loom solemnly before us asserting their rights in the Esperanto of "exclusive rollover minutes", "nationwide long distance", "no roaming charges" and insider local knowledge. The connective tissue that joins one part of the terminal to a commercial centre in downtown Chicago is peeled away, revealing techno-veins and tendrils reaching to the sky. It's a graphic view that offers none of the spectacular openness and flights of fancy associated with the transit lounges located on the departure piers and satellites. Along these circulatory ribbons we experience the still photography and the designer's arrangement of type to attract the eye and lure the body. The blobby diagonals of the telco's logo blend seamlessly with the skyscraper's ribbons of steel, structural exoskeleton and wireless telecommunication cloud.In this plastinated anatomy, the various layers of commercially available techno-space stretch out before the traveller. Here we have no access to the two-way vistas made possible by the gigantic transparent tube structures of the contemporary air terminal. Waiting within the less travelled zones of the circulatory system we find ourselves suspended within the animating system itself. In these arteries and capillaries the flow is spread out and comes close to a halt in the figure of the graphic logo. We know Chicago is connected to us.In the digital logic of packet switching and network effects, there is no reason to privilege the go over the stop, the moving over the waiting. These light box portals do not mirror our bodies, almost at a complete standstill now. Instead they echo the commercial product world that they seek to transfuse us into. What emerges is a new kind of relational aesthetics that speaks to the complex corporeal, temporal, and architectural dimensions of stillness and movement in transit zones: like "a game, whose forms, patterns and functions develop and evolve according to periods and social contexts” (Bourriaud 11). 4. Machine in the CaféIs there a possible line of investigation suggested by the fact that sound waves become visible on the fuselage of jet planes just before they break the sound barrier? Does this suggest that the various human senses are translatable one into the other at various intensities (McLuhan 180)?Here, the technological imaginary contrasts itself with the techno alfresco dining area enclosed safely behind plate glass. Inside the cafes and bars, the best businesses in the world roll out their biggest guns to demonstrate the power, speed and scale of their network coverage (Remmele). The glass windows and light boxes "have the power to arrest a crowd around a commodity, corralling them in chic bars overlooking the runway as they wait for their call, but also guiding them where to go next" (Fuller, "Welcome" 164). The big bulbous plane sits plump in its hangar — no sound barriers broken here. It reassures us that our vehicle is somewhere there in the network, resting at its STOP before its GO. Peeking through the glass wall and sharing a meal with us, this interpenetrative transparency simultaneously joins and separates two planar dimensions — machinic perfection on one hand, organic growth and death on the other (Rowe and Slutsky; Fuller, "Welcome").Bruce Mau is typical in suggesting that the commanding problem of the twentieth century was speed, represented by the infamous image of a US Navy Hornet fighter breaking the sound barrier in a puff of smoke and cloud. It has worked its way into every aspect of the design experience, manufacturing, computation and transport.But speed masks more than it reveals. The most pressing problem facing designers and citizens alike is growth — from the unsustainable logic of infinite growth in GDP to the relentless application of Moore's Law to the digital networks and devices that define contemporary society in the first world. The shift of emphasis from speed to growth as a time-based event with breaking points and moments of rupture has generated new possibilities. "Growth is nonlinear and unpredictable ... Few of us are ready to admit that growth is constantly shadowed by its constitutive opposite, that is equal partners with death” (Mau 497).If speed in part represents a flight from death (Virilio), growth invokes its biological necessity. In his classic study of the persistence of the pastoral imagination in technological America, The Machine in the Garden, Leo Marx charted the urge to idealize rural environments at the advent of an urban industrialised America. The very idea of "the flight from the city" can be understood as a response to the onslaught of technological society and it's deathly shadow. Against the murderous capacity of technological society stood the pastoral ideal, "incorporated in a powerful metaphor of contradiction — a way of ordering meaning and value that clarifies our situation today" (Marx 4). 5. Windows at 35,000 FeetIf waiting and stillness are active forms of bodily engagement, we need to consider the different layers of motion and anticipation embedded in the apprehension of these luminous black-box windows. In The Virtual Window, Anne Friedberg notes that the Old Norse derivation of the word window “emphasizes the etymological root of the eye, open to the wind. The window aperture provides ventilation for the eye” (103).The virtual windows we are considering here evoke notions of view and shelter, open air and sealed protection, both separation from and connection to the outside. These windows to nowhere allow two distinct visual/spatial dimensions to interface, immediately making the visual field more complex and fragmented. Always simultaneously operating on at least two distinct fields, windows-within-windows provide a specialized mode of spatial and temporal navigation. As Gyorgy Kepes suggested in the 1940s, the transparency of windows "implies more than an optical characteristic; it implies a broader spatial order. Transparency means a simultaneous perception of different spatial locations" (Kepes 77).The first windows in the world were openings in walls, without glass and designed to allow air and light to fill the architectural structure. Shutters were fitted to control air flow, moderate light and to enclose the space completely. It was not until the emergence of glass technologies (especially in Holland, home of plate glass for the display of commercial products) that shielding and protection also allowed for unhindered views (by way of transparent glass). This gives rise to the thesis that windows are part of a longstanding architectural/technological system that moderates the dual functions of transparency and separation. With windows, multi-dimensional planes and temporalities can exist in the same time and space — hence a singular point of experience is layered with many other dimensions. Transparency and luminosity "ceases to be that which is perfectly clear and becomes instead that which is clearly ambiguous" (Rowe and Slutsky 45). The light box air-portals necessitate a constant fluctuation and remediation that is at once multi-planar, transparent and "hard to read". They are informatic.From holes in the wall to power lunch at 35,000 feet, windows shape the manner in which light, information, sights, smells, temperature and so on are modulated in society. "By allowing the outside in and the inside out, [they] enable cosmos and construction to innocently, transparently, converge" (Fuller, "Welcome" 163). Laptop, phone, PDA and light box point to the differential mobilities within a matrix that traverses multiple modes of transparency and separation, rest and flight, stillness and speed.6. Can You Feel It?Increasingly the whole world has come to smell alike: gasoline, detergents, plumbing, and junk foods coalesce into the catholic smog of our age (Illich 47).In these forlorn corners of mobile consumption, the dynamic of circulation simultaneously slows and opens out. The surfaces of inscription implore us to see them at precisely the moment we feel unseen, unguided and off-camera. Can you see it, can you feel it, can you imagine the unimaginable, all available to us on demand? Expectation and anticipation give us something to look forward to, but we're not sure we want what's on offer.Air travel radicalizes the separation of the air traveller from ground at one instance and from the atmosphere at another. Air, light, temperature and smell are all screened out or technologically created by the terminal plant and infrastructure. The closer the traveller moves towards stillness, the greater the engagement with senses that may have been ignored by the primacy of the visual in so much of this circulatory space. Smell, hunger, tiredness, cold and hardness cannot be screened out.In this sense, the airplanes we board are terminal extensions, flying air-conditioned towers or groundscrapers jet-propelled into highways of the air. Floating above the horizon, immersed in a set of logistically ordained trajectories and pressurized bubbles, we look out the window and don't see much at all. Whatever we do see, it's probably on the screen in front of us which disconnects us from one space-time-velocity at the same time that it plugs us into another set of relations. As Koolhaas says, junkspace is "held together not by structure, but by skin, like a bubble" (Koolhaas). In these distended bubbles, the traveler momentarily occupies an uncommon transit space where stillness is privileged and velocity is minimized. The traveler's body itself is "engaged in and enacting a whole kaleidoscope of different everyday practices and forms" during the course of this less-harried navigation (Bissell 282).7. Elevator MusicsThe imaginary wheel of the kaleidoscope spins to reveal a waiting body-double occupying the projected territory of what appears to be a fashionable Miami. She's just beyond our reach, but beside her lies a portal to another dimension of the terminal's vascular system.Elevators and the networks of shafts and vents that house them, are to our buildings like veins and arteries to the body — conduits that permeate and structure the spaces of our lives while still remaining separate from the fixity of the happenings around them (Garfinkel 175). The terminal space contains a number of apparent cul-de-sacs and escape routes. Though there's no background music piped in here, another soundtrack can be heard. The Muzak corporation may douse the interior of the elevator with its own proprietary aural cologne, but at this juncture the soundscape is more "open". This functional shifting of sound from figure to ground encourages peripheral hearing, providing "an illusion of distended time", sonically separated from the continuous hum of "generators, ventilation systems and low-frequency electrical lighting" (Lanza 43).There is another dimension to this acoustic realm: “The mobile ecouteur contracts the flows of information that are supposed to keep bodies usefully and efficiently moving around ... and that turn them into functions of information flows — the speedy courier, the networking executive on a mobile phone, the scanning eyes of the consumer” (Munster 18).An elevator is a grave says an old inspector's maxim, and according to others, a mechanism to cross from one world to another. Even the quintessential near death experience with its movement down a long illuminated tunnel, Garfinkel reminds us, “is not unlike the sensation of movement we experience, or imagine, in a long swift elevator ride” (Garfinkel 191).8. States of SuspensionThe suspended figure on the screen occupies an impossible pose in an impossible space: half falling, half resting, an anti-angel for today's weary air traveller. But it's the same impossible space revealed by the airport and bundled up in the experience of flight. After all, the dimension this figures exists in — witness the amount of activity in his suspension — is almost like a black hole with the surrounding universe collapsing into it. The figure is crammed into the light box uncomfortably like passengers in the plane, and yet occupies a position that does not exist in the Cartesian universe.We return to the glossy language of advertising, its promise of the external world of places and products delivered to us by the image and the network of travel. (Remmele) Here we can go beyond Virilio's vanishing point, that radical reversibility where inside and outside coincide. Since everybody has already reached their destination, for Virilio it has become completely pointless to leave: "the inertia that undermines your corporeity also undermines the GLOBAL and the LOCAL; but also, just as much, the MOBILE and the IMMOBILE” (Virilio 123; emphasis in original).In this clinical corner of stainless steel, glass bricks and exit signs hangs an animated suspension that articulates the convergence of a multitude of differentials in one image. 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