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Journal articles on the topic 'Single circular jet'

Author: Grafiati
Published: 4 June 2021
Last updated: 18 February 2022

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1

Hall, David E., Frank P. Incropera, and Raymond Viskanta. "Jet Impingement Boiling From a Circular Free-Surface Jet During Quenching: Part 1—Single-Phase Jet." Journal of Heat Transfer 123, no. 5 (March 22, 2001): 901–10. http://dx.doi.org/10.1115/1.1389061.

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This paper reports results from an experimental study of boiling heat transfer during quenching of a cylindrical copper disk by a subcooled, circular, free-surface water jet. The disk was heated to approximately 650°C, and as quenching occurred, transient temperature measurements were taken at discrete locations near the surface and applied as boundary conditions in a conduction model to deduce transient heat flux distributions at the surface. Results are presented in the form of heat flux distributions and boiling curves for radial locations varying from the stagnation point to ten nozzle diameters for jet velocities between 2.0 and 4.0 m/s 11,300⩽Red⩽22,600. Data for nucleate boiling in the stagnation region and spatial distributions of maximum heat flux are presented and are in good agreement with correlations developed from steady-state experiments. Spatial distributions of minimum film boiling temperatures and heat fluxes are also reported and reveal a fundamental dependence on jet deflection and streamwise location. A companion paper (Hall et al., 2001) describes single-phase and boiling heat transfer measurements from a two-phase (water-air), free-surface, circular jet produced by injecting air bubbles into the jet upstream of the nozzle exit.
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2

Hsieh, Shou-Shing, Jung-Tai Huang, and Huang-Hsiu Tsai. "Heat Transfer of Confined Circular Jet Impingement." Journal of Mechanics 17, no. 1 (March 2001): 29–38. http://dx.doi.org/10.1017/s1727719100002392.

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ABSTRACTExperiments for heat transfer characteristics of confined circular single jet impingement were conducted. The effect of jet Reynolds number, jet hole-to-plate spacing and heat flux levels on heat transfer characteristics of the heated target surface was examined and presented. The local heat transfer coefficient along the surface is measured and correlations of the stagnation point, local and average Nusselt number are developed and discussed. Finally, comparisons of the present data with existing results were also made.
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3

Ikegami, Y., K. Fujita, and M. Ohashi. "Nozzle jet flow-induced vibration of single circular cylinders and twin circular cylinders." Journal of Wind Engineering and Industrial Aerodynamics 49, no. 1-3 (December 1993): 207–16. http://dx.doi.org/10.1016/0167-6105(93)90016-h.

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4

Hall, David E., Frank P. Incropera, and Raymond Viskanta. "Jet Impingement Boiling From a Circular Free-Surface Jet During Quenching: Part 2—Two-Phase Jet." Journal of Heat Transfer 123, no. 5 (March 22, 2001): 911–17. http://dx.doi.org/10.1115/1.1389062.

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A proposed technique for controlling jet impingement boiling heat transfer involves injection of gas into the liquid jet. This paper reports results from an experimental study of boiling heat transfer during quenching of a cylindrical copper specimen, initially at a uniform temperature exceeding the temperature corresponding to maximum heat flux, by a two-phase (water-air), circular, free-surface jet. The second phase is introduced as small bubbles into the jet upstream of the nozzle exit. Data are presented for single-phase convective heat transfer at the stagnation point, as well as in the form of boiling curves, maximum heat fluxes, and minimum film boiling temperatures at locations extending from the stagnation point to a radius of ten nozzle diameters. For void fractions ranging from 0.0 to 0.4 and liquid-only velocities between 2.0 and 4.0 m/s 11,300⩽Red,fo⩽22,600, several significant effects are associated with introduction of the gas bubbles into the jet. As well as enhancing single-phase convective heat transfer by up to a factor of 2.1 in the stagnation region, addition of the bubbles increases the wall superheat in nucleate boiling and eliminates the temperature excursion associated with cessation of boiling. The maximum heat flux is unaffected by changes in the void fraction, while minimum film boiling temperatures increase and film boiling heat transfer decreases with increasing void fraction. A companion paper (Hall et al., 2001) details corresponding results from the single-phase jet.
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5

Chaudhry, Ishtiaq A., and S. Zhong. "A single circular synthetic jet issued into turbulent boundary layer." Journal of Visualization 17, no. 2 (April 5, 2014): 101–11. http://dx.doi.org/10.1007/s12650-014-0199-0.

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6

Manivannan, Ponnambalam, and Banbla Sridhar. "Characteristic study of non-circular incompressible free jet." Thermal Science 17, no. 3 (2013): 787–800. http://dx.doi.org/10.2298/tsci110208116m.

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This paper reports an experimental investigation of bulk properties of turbulent, which is three dimensional, incompressible, air jets issuing into still air surrounding from the nozzles. The jet orifices utilized included circular, hexagonal and cruciform geometries. Experimental results of pertinent mean flow properties such as axis velocity decay, half width growth, potential core and turbulence intensities are reported. Single Hotwire anemometer was used for measurements of the velocity field. The experiment for the three jets was conducted under the same nominal conditions with the exit Reynolds number of 15,400. Consistent with previous investigations of other non circular jets, the cruciform jet is found to have an overall superior mixing capability over the circular counter part. Immediately downstream of the nozzle exit, it entrains, and then mixes with, the surroundings at a higher rate. This jet has a shorter potential core with higher rates of decay and spread than the circular jet. This phenomenon of axis switching is also found to occur in this jet.
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7

Womac, D. J., S. Ramadhyani, and F. P. Incropera. "Correlating Equations for Impingement Cooling of Small Heat Sources With Single Circular Liquid Jets." Journal of Heat Transfer 115, no. 1 (February 1, 1993): 106–15. http://dx.doi.org/10.1115/1.2910635.

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Experimental data have been obtained for liquid jet impingement cooling of small square heat sources resembling electronic integrated circuit chips. Both free-surface and submerged jet configurations have been studied for a range of velocities, nozzle diameters, and nozzle-to-heater separation distances, with water and a fluorocarbon liquid (3M FC-77) as coolants. Major trends in the data have been explained in terms of the underlying hydrodynamic and thermal phenomena. The data, obtained over parameter ranges applicable to the cooling of microelectronic chips, have been compared with the predictions of previously developed correlations for jet impingement heat transfer and substantial discrepancies between the data and the predictions have been noted. Based on the present data, two new correlating equations, one for free-surface and the other for submerged jet impingement, have been developed and presented.
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8

THORPE, S. A., and I. KAVCIC. "The circular internal hydraulic jump." Journal of Fluid Mechanics 610 (August 8, 2008): 99–129. http://dx.doi.org/10.1017/s0022112008002553.

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Circular hydraulic jumps are familiar in single layers. Here we report the discovery of similar jumps in two-layer flows. A thin jet of fluid impinging vertically onto a rigid horizontal plane surface submerged in a deep layer of less-dense miscible fluid spreads radially, and a near-circular internal jump forms within a few centimetres from the point of impact with the plane surface. A jump is similarly formed as a jet of relatively less-dense fluid rises to the surface of a deep layer of fluid, but it appears less stable or permanent in form. Several experiments are made to examine the case of a downward jet onto a horizontal plate, the base of a square or circular container. The inlet Reynolds numbers, Re, of the jet range from 112 to 1790. Initially jumps have an undular, laminar form with typically 2–4 stationary waves on the interface between the dense and less-dense layers but, as the depth of the dense layer beyond the jump increases, the transitions become more abrupt and turbulent, resulting in mixing between the two layers. During the transition to a turbulent regime, single and sometimes moving multiple cusps are observed around the periphery of jumps. A semi-empirical model is devised that relates the parameters of the laboratory experiment, i.e. flow rate, inlet nozzle radius, kinematic viscosity and reduced gravity, to the layer depth beyond the jump and the radius at which an undular jump occurs. The experiments imply that surface tension is not an essential ingredient in the formation of circular hydraulic jumps and demonstrate that stationary jumps can exist in stratified shear flows which can be represented as two discrete layers. No stationary circular undular jumps are found, however, in the case of a downward jet of dense fluid when the overlying, less-dense, fluid is stratified, but a stationary turbulent transition is observed. This has implications for the existence of stationary jumps in continuously stratified geophysical flows: results based on two-layer models may be misleading. It is shown that the Froude number at which a transition of finite width occurs in a radially diverging flow may be less than unity.
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9

Trabold, T. A., and N. T. Obot. "Evaporation of Water With Single and Multiple Impinging Air Jets." Journal of Heat Transfer 113, no. 3 (August 1, 1991): 696–704. http://dx.doi.org/10.1115/1.2910620.

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An experimental investigation of impingement water evaporation under a single jet and arrays of circular jets was made. The parametric study included the effects of jet Reynolds number and standoff spacing for both single and multiple jets, as well as surface-to-nozzle diameter ratio and fractional nozzle open area for single and multiple jets, respectively. The nozzle exit temperature of the air jet, about the same as that of the laboratory, was 3–6° C higher than that of the evaporating water. Predictive equations are provided for mass transfer coefficient in terms of the flow and geometric conditions.
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10

Jambunathan, K., E. Lai, M. A. Moss, and B. L. Button. "A review of heat transfer data for single circular jet impingement." International Journal of Heat and Fluid Flow 13, no. 2 (June 1992): 106–15. http://dx.doi.org/10.1016/0142-727x(92)90017-4.

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11

ICHIMIYA, Koichi. "213 Heat Transfer and Flow Characteristics of a Single Circular Impinging Jet." Proceedings of Conference of Tohoku Branch 2000.35 (2000): 64–65. http://dx.doi.org/10.1299/jsmeth.2000.35.64.

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12

Kareem, Zaid S., Hyder H. Balla, and Ammar F. AbdulWahid. "Heat transfer enhancement in single circular impingement jet by CuO-water nanofluid." Case Studies in Thermal Engineering 15 (November 2019): 100508. http://dx.doi.org/10.1016/j.csite.2019.100508.

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13

Satya Prakash, K. B. V., P. Lovaraju, and E. Rathakrishnan. "Effect of orifice spacing on twin circular parallel compressible jets." International Journal of Turbo & Jet-Engines 38, no. 3 (April 20, 2021): 223–32. http://dx.doi.org/10.1515/tjj-2021-0005.

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Abstract The interaction of Mach 0.5, 0.8, and 1.0, parallel, twin circular jets issuing from orifices with center-to-center spacing S/D, where S is the center-to-center distance and D is orifice diameter, 2, 4 and 6 has been investigated experimentally. The characteristics of twinjets are analyzed based on the centerline Mach number decay, exit Mach number and ratio of orifice spacing. As the spacing between the orifice increases, the maximum Mach number point of the combined jet moves downstream. For the Mach numbers studied it is found that as the S/D increases the effect of the counter-rotating vortices on jet mixing decreases. The rate of the twinjet interaction also decreases with S/D increase. As the jets propagate downstream their center-to-center distance decreases continuously and the jets merge to become single jet, for all S/D studied.
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14

KATE, R. P., P. K. DAS, and SUMAN CHAKRABORTY. "An experimental investigation on the interaction of hydraulic jumps formed by two normal impinging circular liquid jets." Journal of Fluid Mechanics 590 (October 15, 2007): 355–80. http://dx.doi.org/10.1017/s0022112007008063.

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The flow field due to two normal impinging liquid jets is different from the flow field associated with a single normal impinging liquid jet, and even from the flow field around two normal impinging compressible fluid jets. Depending on the spacing between the two jets and their relative strengths, different kinds of hydraulic jump interactions are possible, resulting in a variety of flow patterns. The present study experimentally elucidates the jump--jump interactions formed in such cases, for different values of inter-jet spacings and for different strengths of the individual jets. Analogous flow fields associated with the interactions between a single impinging jet and a fence are also studied to allow convenient experimental flow vizualizations.
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15

Sparrow, E. M., Z. X. Xu, and L. F. A. Azevedo. "Heat (Mass) Transfer for Circular Jet Impingement on a Confined Disk With Annular Collection of the Spent Air." Journal of Heat Transfer 109, no. 2 (May 1, 1987): 329–35. http://dx.doi.org/10.1115/1.3248084.

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Heat (mass) transfer experiments have been performed for a single circular jet impinging perpendicular to a confined disk, with the spent air being collected in an annulus which surrounds the jet delivery tube. This configuration provides precise control of the surface area affected by the impinging jet and also assures complete collection of the spent air. During the course of the experiments, parametric variations were made of the dimensionless separation distance between the jet origin and the impingement disk, of the ratio of disk diameter to the jet diameter, and of the Reynolds number. It was found that the heat (mass) transfer coefficient at the impingement surface increased substantially with a decrease in the jet diameter. Furthermore, for the smaller diameter jet, there was an optimum separation distance at which a maximum value of the heat (mass) transfer coefficient was achieved. For a jet of larger diameter, the transfer coefficient decreased monotonically as the separation distance increased.
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16

Wang, Bing-xing, Qian Xie, Zhao-dong Wang, and Guo-dong Wang. "Fluid flow characteristics of single inclined circular jet impingement for ultra-fast cooling." Journal of Central South University 20, no. 11 (November 2013): 2960–66. http://dx.doi.org/10.1007/s11771-013-1819-x.

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17

Yao, Yufeng, Mohamad Maidi, and Jun Yao. "Effect of Jet Inclination Angle and Hole Exit Shape on Vortical Flow Structures in Low-Reynolds Number Jet in Cross-Flow." Modelling and Simulation in Engineering 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/632040.

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Numerical studies have been performed to visualize vortical flow structures emerged from jet cross-flow interactions. A single square jet issuing perpendicularly into a cross-flow was simulated first, followed by two additional scenarios, that is, inclined square jet at angles of 30° and 60° and round and elliptic jets at an angle of 90°, respectively. The simulation considers a jet to cross-flow velocity ratio of 2.5 and a Reynolds number of 225, based on the free-stream flow quantities and the jet exit width in case of square jet or minor axis length in case of elliptic jet. For the single square jet, the vortical flow structures simulated are in good qualitative agreement with the findings by other researchers. Further analysis reveals that the jet penetrates deeper into the cross-flow field for the normal jet, and the decrease of the jet inclination angle weakens the cross-flow entrainment in the near-wake region. For both noncircular and circular jet hole shapes, the flow field in the vicinity of the jet exit has been dominated by large-scale dynamic flow structures and it was found that the elliptic jet hole geometry has maximum “lifted-off” effect among three hole configurations studied. This finding is also in good qualitative agreement with existing experimental observations.
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18

Yadav, Krishnakumar Rajnath, Akshoy Ranjan Paul, Nithin Hegde, and Anuj Jain. "A Comparison of Circular and Slotted Synthetic Jets for Flow Control in a Twin Air Intake." Defence Science Journal 70, no. 2 (March 9, 2020): 113–21. http://dx.doi.org/10.14429/dsj.70.13053.

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The performance of an aircraft engine depends on air flow quality at the engine face / the exit of the air-intake also known as aerodynamic inlet plane (AIP). A single-engine aircraft has complex Y-shaped twin air-intake which causes severe flow separation, distortion and flow non-uniformity at the AIP. The present study compares the efficacy of slotted synthetic jet and a row of four circular synthetic jets attached to inner faces of a twin air-intake to improve aerodynamic performance at the AIP. The results are obtained using computational fluid dynamics. The velocity and vorticity plots show that lateral spread of the circular jets is limited as compared to the slotted jet. The circular jets are found to be weak as compared to slotted jet to prevent separation of main flow occurring in the twin air-intake. The various aerodynamic performance parameters, such as static pressure recovery coefficient, total pressure loss coefficient, distortion coefficient and secondary flow uniformity are compared for both the cases, exhibiting marked improvement in all these parameters. The study demonstrates that the slotted synthetic jets is a better option for controlling flow in twin air-intake as compared to a row of circular synthetic jets.
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19

Ichimiya, Koichi, Shoichi Takema, Shunichi Morimoto, Tomoaki Kunugi, and Norio Akino. "Movement of impingement heat transfer by a single circular jet with a confined wall." International Journal of Heat and Mass Transfer 44, no. 16 (August 2001): 3095–102. http://dx.doi.org/10.1016/s0017-9310(00)00341-0.

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20

ICHIMIYA, Koichi, Shoichi TAKEMA, Shunichi MORIMOTO, Tomoaki KUNUGI, and Norio AKINO. "Movement of Impingement Heat Transfer by a Single Circular Jet with a Confined Wall." Transactions of the Japan Society of Mechanical Engineers Series B 64, no. 626 (1998): 3350–55. http://dx.doi.org/10.1299/kikaib.64.3350.

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21

Attalla, M., and M. Salem. "Effect of nozzle geometry on heat transfer characteristics from a single circular air jet." Applied Thermal Engineering 51, no. 1-2 (March 2013): 723–33. http://dx.doi.org/10.1016/j.applthermaleng.2012.09.032.

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22

Wang, X. L., J. H. Lee, T. J. Lu, S. J. Song, and T. Kim. "A comparative study of single-/two-jet crossflow heat transfer on a circular cylinder." International Journal of Heat and Mass Transfer 78 (November 2014): 588–98. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.07.014.

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23

Bechtel, S. E. "The Oscillation of Slender Elliptical Inviscid and Newtonian Jets: Effects of Surface Tension, Inertia, Viscosity, and Gravity." Journal of Applied Mechanics 56, no. 4 (December 1, 1989): 968–74. http://dx.doi.org/10.1115/1.3176198.

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The motion of inviscid and Newtonian jets issuing from elliptical orifices is analyzed. The analysis is not confined to small departures of the jet free surface from a circular cylindrical mean surface, but rather is fully nonlinear. Two types of behavior are predicted: (1) In the presence of surface tension the major axis of the elliptical jet cross-section alternates between perpendicular directions with distance down the jet. In this case the system is described as a single-degree-of-freedom nonlinear oscillator, conservative for the inviscid elliptical jet in the absence of gravity, and nonconservative for the Newtonian jet. (2) When surface tension is neglected, the transformation occurs only once, after which the jet flattens into a sheet perpendicular to the major axis of the orifice. The effect of gravity is discussed both for downward flowing jets and fountains.
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24

Myserlis, I., S. Komossa, E. Angelakis, J. L. Gómez, V. Karamanavis, T. P. Krichbaum, U. Bach, and D. Grupe. "High cadence, linear, and circular polarization monitoring of OJ 287." Astronomy & Astrophysics 619 (November 2018): A88. http://dx.doi.org/10.1051/0004-6361/201732273.

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Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Here, we analyze the evolution in total flux density, linear and circular polarization as a means to study the OJ 287 jet structure and its magnetic field geometry. Methods. We used a recently developed, high-precision data analysis methodology to recover all four Stokes parameters. We measured the total flux density of OJ 287 at nine bands from 2.64 GHz to 43 GHz, the linear polarization parameters at four bands between 2.64 GHz and 10.45 GHz, and the circular polarization at two bands, 4.85 GHz and 8.35 GHz. The mean cadence of our measurements is ten days. Results. Between December 2015 and January 2017 (MJD 57370–57785), OJ 287 showed flaring activity and complex linear and circular polarization behavior. The radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by ∼340° with a mean rate of −1.04°/day. Based on concurrent very long baseline interferometric (VLBI) polarization data at 15 GHz and 43 GHz, the rotation seems to originate within the jet core at 43 GHz (projected angular size ≤0.15 mas or 0.67 pc at the redshift of the source). Moreover, optical polarization data show a similar monotonic CW rotation with a rate of about −1.1°/day which is superposed with shorter and faster rotations that exhibit rates of about 7.8°/day, mainly in the CW sense. Conclusions. The flux density and polarization variability of the single dish, VLBI and optical data is consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length to 0.26 pc and radius to ≤0.04 pc as well as the jet bending arc length projected on the plane of the sky to ≤1.9–7.6 pc. A similar bending has been observed also in high angular resolution VLBI images of the OJ 287 jet at its innermost regions. The helical trajectory covers only a part of the jet width, possibly its spine. In addition, our results indicate the presence of a stable polarized emission component. Its EVPA (−10°) is oriented perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component. Finally, the EVPA rotation begins simultaneously with an optical flare and hence the two might be physically connected. That optical flare has been suggested to be linked to the interaction of a secondary SMBH with the inner accretion disk or originating in the jet of the primary.
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25

Sung, Myung Ki, and Issam Mudawar. "Effects of jet pattern on single-phase cooling performance of hybrid micro-channel/micro-circular-jet-impingement thermal management scheme." International Journal of Heat and Mass Transfer 51, no. 19-20 (September 2008): 4614–27. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2008.02.021.

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26

BERGMANN, RAYMOND, ERIK DE JONG, JEAN-BAPTISTE CHOIMET, DEVARAJ VAN DER MEER, and DETLEF LOHSE. "The origin of the tubular jet." Journal of Fluid Mechanics 600 (March 26, 2008): 19–43. http://dx.doi.org/10.1017/s0022112008000347.

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A vertical cylindrical tube is partially immersed in a water-filled container and pressurized to lower the fluid level inside the tube. A sudden release of the pressure in the tube creates a singularity on top of the rising free surface. At the very beginning of the process a jet emerges at the centre of the surface, the strength of which strongly depends on the initial shape of the meniscus. Here, the time-evolution of the complex shape of the free surface and the flow around the cylindrical tube are analysed using high-speed imaging, particle image velocimetry, and numerical simulations. The tubular jet is found to be created by the following series of events, which eventually lead to the flow focusing at the tube's centre. A circular surface wave, produced by the funnelling of flow into the tube, is pushed inwards by the radial flow directly underneath the surface. As the wave moves inward and eventually collapses at the centre of the tube, a bump of fluid grows in the centre due to the converging flow in the bulk. This converging flow continues to feed the jet after the circular wave has collapsed. The singularity of the wave collapse is manifested in the initial sharp tip of the jet. All of the above events are traced back to a single origin: the convergence of the flow as it enters the tube. Movies are available with the online version of the paper.
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27

Al-Dulaimi, M. J., F. A. Hamad, A. A. Abdul Rasool, and K. A. Ameen. "Effect of sand particles on flow structure of free jet from a nozzle." Journal of Mechanical Engineering and Sciences 13, no. 3 (September 27, 2019): 5542–61. http://dx.doi.org/10.15282/jmes.13.3.2019.21.0447.

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The Characteristics of single and two- phase flow from a circular turbulent free jet from a nozzle of 10 mm diameter were investigated experimentally and numerically. The measurements were conducted for ReJ = 10007 - 31561. The velocity was measured at location from the nozzle y/D (0-8) in axial and radial directions. The two phase measurement were done by using natural construction sand as a solid phase of sizes (220,350,550) µm and loading ratios (mass flow ratio of sand to mass flow rate of air) in the range (0.18-1.38). Two phase air velocity of jet showed that the introducing of natural sand particles gives lower jet velocity attributed to momentum transfer to particles. The smaller particle size leads to lower values of velocity. The velocity found to be decreased with loading ratio increase. The numerical simulation was performed for single and two phase jet flow. RNG K-ε turbulence model was used to simulate the flow of fluid and the discrete phase model to simulate the particles flow. The results form numerical simulation showed a good agreement with experimental results.
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28

Grinshpun, S. A., G. Mainelis, M. Trunov, R. L. Górny, S. K. Sivasubramani, A. Adhikari, and T. Reponen. "Collection of airborne spores by circular single-stage impactors with small jet-to-plate distance." Journal of Aerosol Science 36, no. 5-6 (May 2005): 575–91. http://dx.doi.org/10.1016/j.jaerosci.2004.06.078.

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29

Nagesha, K., K. Srinivasan, and T. Sundararajan. "Heat transfer characteristics of single circular jet impinging on a flat surface with a protrusion." Heat and Mass Transfer 56, no. 6 (January 28, 2020): 1901–20. http://dx.doi.org/10.1007/s00231-020-02814-z.

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30

Florschuetz, L. W., and C. C. Su. "Effects of Crossflow Temperature on Heat Transfer Within an Array of Impinging Jets." Journal of Heat Transfer 109, no. 1 (February 1, 1987): 74–82. http://dx.doi.org/10.1115/1.3248072.

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Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. In the experimental model the jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. In addition to the crossflow that originated from the jets following impingement, an initial crossflow was present that approached the array through an upstream extension of the channel. By varying the initial crossflow temperature, the mixed-mean crossflow temperature approching each spanwise jet row n (Tm,n) was varied independently of the jet temperature (Tj). For each row, the effect of Tm,n relative to Tj on the heat flux opposite the row was determined. Results are formulated in terms of parameters defined for each individual spanwise row domain: a crossflow-to-jet temperature difference influence factor (ηr) and a Nusselt number (Nur) as functions of jet Reynolds number, crossflow-to-jet mass flux ratio, and geometric parameters. Effects of row position within the array are also considered. It was found that ηr and Nur are nominally independent of row position after the first two rows.
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31

Ekkad, Srinath V., Shichuan Ou, and Richard B. Rivir. "Effect of Jet Pulsation and Duty Cycle on Film Cooling From a Single Jet on a Leading Edge Model." Journal of Turbomachinery 128, no. 3 (January 25, 2006): 564–71. http://dx.doi.org/10.1115/1.2185122.

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The effect of jet pulsation and duty cycle on film effectiveness and heat transfer was investigated on a film hole located on the circular leading edge of a blunt body. A transient infrared technique was used to measure both heat transfer coefficients and film effectiveness from a single test. Detailed Frossling number and film effectiveness distributions were obtained for all flow conditions. Jet pulsing frequencies of 5 Hz, 10 Hz, and 20 Hz have been studied. The effect of duty cycle created by the valve opening and closing times was also set at different levels of 10%, 25%, 50%, and 75% of designated 100% fully open condition for different blowing ratios from 0.25 to 2.0. The combination of pulse frequency and duty cycle was investigated for different blowing ratios on a single leading edge hole located at 22 deg from geometric leading edge. Results indicate that higher effectiveness and lower heat transfer coefficients are obtained at the reduced blowing ratios, which result from reduced duty cycles. The effect of varying the pulsing frequency from 5 Hz to 20 Hz is not discernable beyond the level of experimental uncertainty. Effective blowing ratio due to lowering of the duty cycle at a given blowing ratio seems to play a more important role in combination with pulsing, which provides improved cooling effectiveness at lower heat transfer coefficients.
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32

ICHIMIYA, Koichi, and Yoshio NAKAMURA. "Heat Transfer of a Single Circular Impinging Jet Considered on Heat Conduction in a Heated Plate." Transactions of the Japan Society of Mechanical Engineers Series B 58, no. 550 (1992): 2031–35. http://dx.doi.org/10.1299/kikaib.58.2031.

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33

Parsons, J. A., J. C. Han, and C. P. Lee. "Rotation Effect on Jet Impingement Heat Transfer in Smooth Rectangular Channels With Four Heated Walls and Radially Outward Crossflow." Journal of Turbomachinery 120, no. 1 (January 1, 1998): 79–85. http://dx.doi.org/10.1115/1.2841392.

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The effect of channel rotation on jet impingement cooling by arrays of circular jets in two channels was studied. Jet flow direction was in the direction of rotation in one channel and opposite to the rotation direction in the other channel. The jets impinged normally on two smooth target walls. Heat transfer results are presented for these two target walls, for the jet walls containing the jet producing orifices, and for side walls, connecting the target and jet walls. The flow exited the channels in a single direction, radially outward, creating a crossflow on jets at larger radii. The mean test model radius-to-jet diameter ratio was 397. The jet rotation number was varied from 0.0 to 0.0028 and the isolated effects of jet Reynolds number (5000 and 10,000), and wall-to-coolant temperature difference ratio (0.0855 and 0.129) were measured. The results for nonrotating conditions show that the Nusselt numbers for the target and jet walls in both channels are about the same and are greater than those for the side walls of both channels. However, as rotation number increases, the heat transfer coefficients for all walls in both channels decrease up to 20 percent below those results that correspond to nonrotating conditions. As the wall-to-coolant temperature difference ratio increases, heat transfer coefficient decreases up to 10 percent with other parameters held constant.
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34

Ichimiya, Koichi, and Yoshio Yamada. "Three-Dimensional Heat Transfer of a Confined Circular Impinging Jet With Buoyancy Effects." Journal of Heat Transfer 125, no. 2 (March 21, 2003): 250–56. http://dx.doi.org/10.1115/1.1527901.

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This paper describes the heat transfer and flow characteristics of a single circular laminar impinging jet including buoyancy force in a comparatively narrow space with a confined wall. Temperature distribution and velocity vectors in the space were obtained numerically by solving three-dimensional governing equations for the Reynolds number Re=umD/ν=400-2000 and the dimensionless space, H=h/D=0.25-1.0. After impingement, heat transfer behavior on the impingement surface is divided into a forced convection region, a mixed convection region, and a natural convection region in the radial direction. The local heat flux corresponding to these three regions was visualized using a thermosensitive liquid crystal. Moreover, with the increase in Reynolds number, Re, and dimensionless space, H, the recirculation flow on the impingement surface moves downstream and its volume increases correspondingly. The Nusselt number averaged from r=0 to the minimum point of peripherally averaged Nusselt number, Num, was evaluated as a function of Re and H.
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35

Raman, G., S. Packiarajan, G. Papadopoulos, C. Weissman, and S. Raghu. "Jet thrust vectoring using a miniature fluidic oscillator." Aeronautical Journal 109, no. 1093 (March 2005): 129–38. http://dx.doi.org/10.1017/s0001924000000634.

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Abstract This paper presents a new approach to vectoring jet thrust using a miniature fluidic actuator that provided spatially distributed mass addition. The fluidic actuators used had no moving parts and produced oscillatory flow with a square wave form at frequencies up to 1·6kHz. A subsonic jet with an exit diameter of 3·81cm was controlled using single and dual fluidic actuators, each with an equivalent circular diameter of 1·06mm. The fluidic nozzle was operated at pressures between 20·68 and 165·47kPa. The objectives of the present work included documentation of the actuation characteristics of fluidic devices, assessment of the effectiveness of fluidic devices for jet thrust vectoring, and evaluation of mass flow requirements for vectoring under various conditions. Measurements were made in the flow field using a pitot probe for the vectored and unvectored cases. Some acoustic measurements were made using microphones in the near-field and for selected cases particle image velocimetry (PIV) measurements were made. Thrust vectoring was obtained in low speed jets by momentum effects with fluidic device mass flow rates of only 2 × 10–4kg/sec (0·6% of main jet mass flow per fluidic oscillator). Although a single fluidic device produced vectoring of the primary jet, the dual fluidic device configuration (with two fluidic devices on either side of the jet exit) produced mass flux enhancement of 28% with no vectoring. Our results indicate that fluidic actuators have the potential for use in thrust vectoring, flow mixing and industrial flow deflection applications.
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36

Dhondoo, Nilesh, Ştefan-Mugur Simionescu, and Corneliu Bălan. "Impinging jets array: an experimental investigation and numerical modeling." E3S Web of Conferences 85 (2019): 05004. http://dx.doi.org/10.1051/e3sconf/20198505004.

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This paper reports on the measurements of wall shear stress and static pressure along a smooth static wall upon which jet impingement occurs. The effect of a single circular jet, respectively an array of jets is studied using a high speed/resolution camera. The areas of interest are the stagnation region and the wall jet region, where the jet is deflected from axial to radial direction. The effect of increasing the distance between the inlets is also investigated. The results are obtained by performing direct flow experimental visualizations and CFD numerical simulations, using the Reynolds averaged Navier-Stokes (RANS) approach with the commercial software ANSYS Fluent. The findings suggest that the smaller the nozzle-to-wall distance is, the higher the pressure peak. The wall shear stress has a bimodal distribution; at stagnation point, the wall shear stress is 0. An increase in the number of inlets produces the effect of a decrease in the stagnation point pressure. The greater the inter-inlet distance is, the greater the stagnation point pressure (there is less inter-jet mixing, less energy is lost in vortices formed between jets).
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37

Sheriff, H. S., and D. A. Zumbrunnen. "Local and Instantaneous Heat Transfer Characteristics of Arrays of Pulsating Jets." Journal of Heat Transfer 121, no. 2 (May 1, 1999): 341–48. http://dx.doi.org/10.1115/1.2825986.

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Recent investigations have revealed that pulsations in an incident jet flow can be an effective technique for modifying convective heat transfer characteristics. While these studies focused on single impinging jets, industrial applications of impinging jets usually involve arrays of jets. To explore the effects of flow pulsations on the heat transfer performance of jet arrays, an experimental investigation has been performed of instantaneous and time-averaged convective heat transfer to a square, in-line array of circular air jets within an unit cell of the array. Hot-film anemometry was used to document the jet flow field. Instantaneous and time-averaged convective heat transfer rates were measured using a heat flux microsensor. An ensemble averaging technique was used to separate the pulsating component of flow velocity and heat transfer from the turbulent components and thereby assess the effect of flow pulsation on turbulence intensity and heat transfer. For the ranges of parameters considered, results indicate convective heat transfer distributions become more uniform in response to pulsations but heat transfer is not enhanced. Improved uniformity can be a useful aspect in many jet applications.
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38

Tseng, L. Y., A. S. Yang, and J. C. Lin. "Study of a Crossflow over a Zero-Net-Mass-Flux Synthetic Jet Driven by a Vibrating Diaphragm." Journal of Mechanics 27, no. 4 (December 2011): 503–9. http://dx.doi.org/10.1017/jmech.2011.53.

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ABSTRACTMiniature synthetic jet actuators are low operating power, zero-net-mass-flux and very compact devices which have demonstrated their capability in modifying the subsonic flow characteristics for boundary layer flow control. In order to improve the design active flow control systems, the present study aims to examine the formation and interaction of unsteady flowfield of a synthetic jet with external crossflow. In view of a single synthetic jet emitting into a turbulent boundary layer crossflow via a circular orifice, the theoretical model utilized the transient three-dimensional conservation equations of mass and momentum for compressible, turbulent flows with a negligible temperature variation over the computational domain. The motion of a movable membrane plate was also treated as the moving boundary by prescribing the displacement on the plate surface. The predictions by the computational fluid dynamics (CFD) software ACE+®were compared with the measured transient phase-averaged velocities in literature for code validation. The predictions showed the time evolution of the large vortical structure originating from the jet orifice and its successive interaction with the crossflow to change the flow structure inside the boundary layer.
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39

Fabre, David, Raffaele Longobardi, Paul Bonnefis, and Paolo Luchini. "The acoustic impedance of a laminar viscous jet through a thin circular aperture." Journal of Fluid Mechanics 864 (February 1, 2019): 5–44. http://dx.doi.org/10.1017/jfm.2018.1008.

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The unsteady axisymmetric flow through a circular aperture in a thin plate subjected to harmonic forcing (for instance under the effect of an incident acoustic wave) is a classical problem first considered by Howe (Proc. R. Soc. Lond. A, vol. 366, 1979, pp. 205–223), using an inviscid model. The purpose of this work is to reconsider this problem through a numerical resolution of the incompressible linearized Navier–Stokes equations (LNSE) in the laminar regime, corresponding to $Re=[500,5000]$. We first compute a steady base flow which allows us to describe the vena contracta phenomenon in agreement with experiments. We then solve a linear problem allowing us to characterize both the spatial amplification of the perturbations and the impedance (or equivalently the Rayleigh conductivity), which is a key quantity to investigate the response of the jet to acoustic forcing. Since the linear perturbation is characterized by a strong spatial amplification, the numerical resolution requires the use of a complex mapping of the axial coordinate in order to enlarge the range of Reynolds number investigated. The results show that the impedances computed with $Re\gtrsim 1500$ collapse onto a single curve, indicating that a large Reynolds number asymptotic regime is effectively reached. However, expressing the results in terms of conductivity leads to substantial deviation with respect to Howe’s model. Finally, we investigate the case of finite-amplitude perturbations through direct numerical simulations (DNS). We show that the impedance predicted by the linear approach remains valid for amplitudes up to order $10^{-1}$, despite the fact that the spatial evolution of the perturbations in the jet is strongly nonlinear.
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40

PHILIPP, A., and W. LAUTERBORN. "Cavitation erosion by single laser-produced bubbles." Journal of Fluid Mechanics 361 (April 25, 1998): 75–116. http://dx.doi.org/10.1017/s0022112098008738.

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In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary (γ=2, where γ=s/Rmax, s is the distance between the boundary and the bubble centre at the moment of formation and Rmax is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances (γ[les ]0.7). In this region, the impact velocity rises to 83 m s−1, corresponding to a water hammer pressure of about 0.1 GPa, whereas at γ>1, the impact velocity is smaller than 25 m s−1. The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when γ<2 and at the moment of first collapse when γ<1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range γ=1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At γ[les ]1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the circumference of the torus, the observed damage is circular as well. Bubbles in the ranges γ[les ]0.3 and γ=1.2 to 1.4 caused the greatest damage. The overall diameter of the damaged area is found to scale with the maximum bubble radius. Owing to the possibility of generating thousands of nearly identical bubbles, the cavitation resistance of even hard steel specimens can be tested.
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41

Gibson, Alex, Wolfgang Neubauer, Sebastian Flöry, Petra Schneidhofer, Mike Allen, Enid Allison, Wendy Carruthers, et al. "SURVEY AND SAMPLING AT THE CASTLE DYKES IRON AGE ‘HENGE’, WENSLEYDALE, NORTH YORKSHIRE." Antiquaries Journal 99 (April 15, 2019): 1–31. http://dx.doi.org/10.1017/s0003581518000628.

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Survey and sampling at the classic single-entranced henge monument at Castle Dykes, in North Yorkshire, has revealed traces of circular timber structures, interpreted as later prehistoric roundhouses, in the immediate vicinity and within the henge. Coring of the waterlogged silts of the internal ditch has produced considerable environmental data: plant, insect, pollen and charcoal remains. A small jet bead was also recovered. Radiocarbon dates from short-lived materials unexpectedly indicate that the monument was constructed in the Iron Age, which prompts a review of other potentially Iron Age ‘henges’ further afield.
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42

Florschuetz, L. W., and H. H. Tseng. "Effect of Nonuniform Geometries on Flow Distributions and Heat Transfer Characteristics for Arrays of Impinging Jets." Journal of Engineering for Gas Turbines and Power 107, no. 1 (January 1, 1985): 68–75. http://dx.doi.org/10.1115/1.3239699.

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Two-dimensional arrays of circular jets impinging on a surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the impingement surface. Experimental results for the effects of streamwise nonuniform array geometries on streamwise flow distributions and heat transfer characteristics are presented. A flow distribution model for nonuniform arrays is developed and validated by comparison with the measured flow distributions. The model is then employed to compare nonuniform array streamwise resolved heat transfer coefficient data with previously reported uniform array data and with a previously developed correlation based on the uniform array data. It was found that uniform array results can, in general, serve as a satisfactory basis from which to predict heat transfer coefficients at individual spanwise rows of nonuniform arrays. However, significant differences were observed in some cases over the first one or two rows downstream of the geometric transition line of the nonuniform array.
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43

Tsai, Feng Chin, and Rong Fung Huang. "Topological Flow Structures of Annular Swirling Jets." Journal of Mechanics 17, no. 3 (September 2001): 131–38. http://dx.doi.org/10.1017/s1727719100004494.

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AbstractThe effects of blockage and swirl on the macro flow structures of the annular jet past a circular disc are experimentally studied through the time-averaged streamline patterns. In the blockage-effect regime, the flows present multiple modes, single bubble, dual rings, vortex breakdown, and triple rings, in different regimes of blockage ratio and swirl number. The topological models of the flow structures are proposed and discussed according to the measured flow fields to manifest the complex flow structures. The single bubble is a closed recirculation bubble with a stagnation point on the central axis. The dual-ring flow is an open-top recirculsation zone, in which a pair of counter-rotating vortex rings exists in the near wake. The fluids in the dual rings are expelled downstream through a central jet-like swirling flow. A vortex breakdown may occur in the central jet-like swirling flow if the exit swirl number exceeds critical values. When the vortex breakdown interacts with the dual rings, a complex triple-ring flow structure forms. Axial distributions of the local swirl number are presented and discussed. The local swirl number increases with the increase of the exit swirl number and attains the maximum in the dual-ring mode. At large exit swirl numbers where the vortex breakdown occurs, the local swirl number decreases drastically to a low value.
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44

WU, XUESONG, and PATRICK HUERRE. "Low-frequency sound radiated by a nonlinearly modulated wavepacket of helical modes on a subsonic circular jet." Journal of Fluid Mechanics 637 (September 23, 2009): 173–211. http://dx.doi.org/10.1017/s0022112009990577.

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A possible fundamental physical mechanism by which instability modes generate sound waves in subsonic jets is presented in the present paper. It involves a wavepacket of a pair of helical instability modes with nearly the same frequencies but opposite azimuthal wavenumbers. As the wavepacket undergoes simultaneous spatial–temporal development in a circular jet, the mutual interaction between the helical modes generates a strong three-dimensional, slowly modulating ‘mean-flow distortion’. It is demonstrated that this ‘mean field’ radiates sound waves to the far field. The emitted sound is of very low frequency, with characteristic time and length scales being comparable with those of the envelope of the wavepacket, which acts as a non-compact source. A matched-asymptotic-expansion approach is used to determine, in a self-consistent manner, the acoustic field in terms of the envelope of the wavepacket and a transfer factor characterizing the refraction effect of the background base flow. For realistic jet spreading rates, the nonlinear development of the wavepacket is found to be influenced simultaneously by non-parallelism and non-equilibrium effects, and so a composite modulation equation including both effects is constructed in order to describe the entire growth–attenuation–decay cycle. Parametric studies pertaining to relevant experimental conditions indicate that the acoustic field is characterized by a single-lobed directivity pattern beamed at an angle about 45°–60° to the jet axis and a broadband spectrum centred at a Strouhal number St ≈ 0.07–0.2. As the nonlinear effect increases, the radiation becomes more efficient and the noise spectrum broadens, but the gross features of the acoustic field remain robust, and are broadly in agreement with experimental observations.
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45

Ghasemi, Abbas, Burak Ahmet Tuna, and Xianguo Li. "Curvature-induced deformations of the vortex rings generated at the exit of a rectangular duct." Journal of Fluid Mechanics 864 (February 1, 2019): 141–80. http://dx.doi.org/10.1017/jfm.2018.988.

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Rectangular air jets of aspect ratio $2$ are studied at $Re=UD_{h}/\unicode[STIX]{x1D708}=17\,750$ using particle image velocimetry and hot-wire anemometry as they develop naturally or under acoustic forcing. The velocity spectra and the spatial theory of linear stability characterize the fundamental ($f_{n}$) and subharmonic ($f_{n}/2$) modes corresponding to the Kelvin–Helmholtz roll-up and vortex pairing, respectively. The rectangular cross-section of the jet deforms into elliptic/circular shapes downstream due to axis switching. Despite the apparent rotation of the vortex rings or the jet cross-section, the axis-switching phenomenon occurs due to reshaping into rounder geometries. By enhancing the vortex pairing, excitation at $f_{n}/2$ shortens the potential core, increases the jet spread rate and eliminates the overshoot typically observed in the centreline velocity fluctuations. Unlike circular jets, the skewness and kurtosis of the rectangular jets demonstrate elevated anisotropy/intermittency levels before the end of the potential core. The axis-switching location is found to be variable by the acoustic control of the relative expansion/contraction rates of the shear layers in the top (longer edge), side (shorter edge) and diagonal views. The self-induced vortex deformations are demonstrated by the spatio-temporal evolution of the phase-locked three-dimensional ring structures. The curvature-induced velocities are found to reshape the vortex ring by imposing nonlinear azimuthal perturbations occurring at shorter wavelengths with time/space evolution. Eventually, the multiple high-curvature/high-velocity regions merge into a single mode distribution. In the plane of the top view, the self-induced velocity distribution evolves symmetrically while the tilted ring results in the asymmetry of the azimuthal perturbations in the side view as the side closer to the acoustic source rolls up in more upstream locations.
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46

Pribytkov, I. A., and S. I. Kondrashenko. "ON THE CALCULATION OF CONVECTIVE HEAT TRANSFER UNDER MUTUAL-ACTION OF A JET WITH LIMITING SURFACE." Izvestiya. Ferrous Metallurgy 62, no. 3 (June 20, 2019): 208–14. http://dx.doi.org/10.17073/0368-0797-2019-3-208-214.

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The paper proposes a method for calculating convective heat transfer in the interaction of a single circular jet with a flat surface. The differences of the proposed method from the existing ones are given. The concepts “energodynamic potential of the flow” and “energodynamic power of the flow” are introduced, allowing to determine the intensity of convective heat transfer at “gas-solid” boundary. Differences of the proposed definitions from the existing ones are given: heat flux and heat flux density. The principal difference between the heat flux density q and the energy dynamic potential qэ is as follows: the heat flux density q for convective heat transfer problems means the amount of heat that is transferred from a liquid to a solid surface (or vice versa) per unit of time through a unit of heat exchange surface area. Thus, quantity q characterizes the intensity of convective heat transfer process at the interface. The energy dynamic potential qэ characterizes the flow property as a source or carrier of heat. Value of qэ characterizes the specific energy power of the fluid flow. When calculating the heat transfer, it was proposed to divide the jet when interacting with the flat surface into two parts: before the interaction – the jet part, after – the fan flow. The method for calculating convective heat transfer under jet heating, in which the Reynolds criterion calculated by characteristics of the gas at the nozzle exit is decisive, is not entirely correct. It is proposed to use criteria specific to the fan flow. Characteristic values for the fan flow are its initial average velocity Uвп, distance from the critical point of the jet (point of intersection of vertical axis of the jet with the surface) to the current coordinate of radius downstream. To assess the changes in basic characteristics of a free jet at different distances from the nozzle exit to limiting surface, dependences of the following criteria are presented: jet expansion coefficient; jet injection coefficient; velocity coefficient for any jet section; velocity coefficient for any jet section, except h/d0 = 0; relation of the Reynolds criteria, confirming the need to carry out calculations of heat transfer on the values characteristic separately for the fan flow.
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47

ICHIMIYA, Koichi, and Yoshio YAMADA. "Three-Dimensional Characteristics of Heat Transfer and Flow and Visualization on a Single Circular Laminar Impinging Jet in Comparatively Narrow Space." Journal of the Visualization Society of Japan 20, no. 78 (2000): 250–55. http://dx.doi.org/10.3154/jvs.20.250.

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48

Pan, Kang, and James S. Wallace. "Numerical studies of the ignition characteristics of a high-pressure gas jet in compression ignition engines with glow plug ignition assist: Part 2-Effects of multi-opening glow plug shields." International Journal of Engine Research 19, no. 9 (October 26, 2017): 977–1001. http://dx.doi.org/10.1177/1468087417736997.

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The results of a previous study, part 1, showed that use of a shield can improve the thermal performance of a glow plug, and thereby reduce ignition time. However, the part 1 study also found that use of a simple shield with only one circular opening can delay flame propagation out of the shield. The conclusions of that study suggested that there is scope for further improvements of the shield design, especially the shield opening geometry. Accordingly, this article presents the results of computational studies investigating the influence of multi-opening shield designs on natural gas ignition characteristics in glow plug–assisted compression–ignition engines. Two types of multi-opening glow plug shield, consisting of four small circular openings distributed in either diamond-pattern or square-pattern arrangements, were employed. The simulated results demonstrated that both multi-opening shields can not only increase glow plug surface temperature, but also increase the residence time of fuel mixture adjacent to the glow plug surface in the early injection stage, resulting in a faster ignition than the single-opening shield. Furthermore, the diamond-pattern multi-opening glow plug shield provides a faster or comparable flame propagation path back to combustion chamber, compared to single-opening glow plug shield, while the square-pattern multi-opening glow plug shield delays the flame propagation under several specific engine conditions. Compared to the single-opening glow plug shield, the overall natural gas ignition delays are further reduced by 6%–44% when using the diamond-pattern multi-opening glow plug shield, while the square-pattern multi-opening glow plug shield is only able to reduce the natural gas ignition delay under a few specific conditions.
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49

Habera, Łukasz, and Kamil Hebda. "Badania porównawcze liniowych ładunków kumulacyjnych." Nafta-Gaz 77, no. 6 (June 2021): 366–75. http://dx.doi.org/10.18668/ng.2021.06.02.

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The fireground tests are the best method for verifying the operation effectiveness of the entire shooting device or its component parts in real conditions. The purpose of the fireground tests presented herein was the physical verification of linear shaped charge (LSC) ability to perforate multi-layered target, reflecting the material and geometrical conditions of a borehole. The series of shooting tests included tests of three types of linear shaped charges selected for use in perfo-fracturing devices. The following shaped charges were tested: LSC in lead enclosure, having φ = 40 mm circular cross-section with shaped recess; LSC with copper liner in 20/30 mm steel trapezoid enclosure; LSC with liner made of solid copper, in 20/40 mm steel trapezoidal enclosure.During testing, the cumulative jet velocity was recorded using voltage type probes, arranged between the individual layers of a target composed of steel and concrete materials. The research method adapted for the project purposes was aimed at verification of the following thesis: whether the proposed shaped charges fulfil the technical and performance conditions for their effective application in the oil industry. The criterion adopted was the ability – or lack of ability – to perforate the multi-layered barrier in the form of two steel plates and concrete casting. The testing stand, single-use by its nature, was each time composed of concrete block having 400 mm ´ 250 mm ´ 150 mm dimensions and 20 MPa static compressive strength, on which two steel plates were placed parallel to each other with 20 mm spacing. The thickness of the plates was 5 mm and 10 mm respectively. The tested shaped charge was placed on the top steel plate at a distance of one calibre – that is the distance equal to the opening of the trapezoidal shaped charge and full diameter of circular cross-section charge. Furthermore, within media interface planes (steel/air, air/steel; steel/concrete), the set of voltage-type measuring probes was installed, in the form of single electric wires (φ = 0.25 mm). At an instant when they break (circuit break) as a result of cumulative jet operation, voltage drop in the subsequent measuring probes will act as a logical gate of start-stop type, or in other words the zero-one (0–1) type gate. The readings of individual probes breakage times allowed in addition to determine the velocity of the cumulative jet and to estimate its braking dynamics while passing through the subsequent elements of multi-layered target.
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50

Chang, Yu-Teng, Rong-Tsu Wang, and Jung-Chang Wang. "PMMA Application in Piezo Actuation Jet for Dissipating Heat of Electronic Devices." Polymers 13, no. 16 (August 5, 2021): 2596. http://dx.doi.org/10.3390/polym13162596.

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The present study utilizes an acrylic (PMMA) plate with circular piezoelectric ceramics (PC) as an actuator to design and investigate five different types of piezo actuation jets (PAJs) with operating conditions. The results show that the heat transfer coefficient of a device of PAJ is 200% greater than that of a traditional rotary fan when PAJ is placed at the proper distance of 10 to 20 mm from the heat source, avoiding the suck back of surrounding fluids. The cooling effect of these five PAJs was calculated by employing the thermal analysis method and the convection thermal resistance of the optimal PAJ can be reduced by about 36%, while the voltage frequency, wind speed, and noise were all positively correlated. When the supplied piezoelectric frequency is 300 Hz, the decibel level of the noise is similar to that of a commercial rotary fan. The piezoelectric sheets had one of two diameters of 31 mm or 41 mm depending on the size of the tested PAJs. The power consumption of a single PAJ was less than 10% of that of a rotary fan. Among the five types of PAJ, the optimal one has the characteristics that the diameter of the piezoelectric sheet is 41 mm, the piezoelectric spacing is 2 mm, and the length of the opening is 4 mm. Furthermore, the optimal operating conditions are a voltage frequency of 300 Hz and a placement distance of 20 mm in the present study.
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