Academic literature on the topic 'Viscount (Transport plane)'
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Journal articles on the topic "Viscount (Transport plane)"
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Zaks, Michael A., and Alexander Nepomnyashchy. "Subdiffusive and superdiffusive transport in plane steady viscous flows." Proceedings of the National Academy of Sciences 116, no. 37 (March 19, 2018): 18245–50. http://dx.doi.org/10.1073/pnas.1717225115.
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Deterministic transport of passive tracers in steady laminar plane flows of incompressible viscous fluids through lattices of solid bodies or arrays of steady vortices can be anomalous. Motion along regular patterns of streamlines is often aperiodic: Repeated slow passages near stagnation points and/or solid surfaces serve for eventual decorrelation. Singularities of passage times near the obstacles, dictated by the boundary conditions, affect the character of transport anomalies: Flows past arrays of vortices are subdiffusive whereas tracers advected through lattices of solid obstacles can feature superdiffusion. We calculate the transport characteristics with the help of the simple and computationally efficient model: the special flow.
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Liu, Chun-Ho. "Turbulent Plane Couette Flow and Scalar Transport at Low Reynolds Number." Journal of Heat Transfer 125, no. 6 (November 19, 2003): 988–98. http://dx.doi.org/10.1115/1.1571084.
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The turbulence structure and passive scalar (heat) transport in plane Couette flow at Reynolds number equal to 3000 (based on the relative speed and distance between the walls) are studied using direct numerical simulation (DNS). The numerical model is a three-dimensional trilinear Galerkin finite element code. It is found that the structures of the mean velocity and temperature in plane Couette flow are similar to those in forced channel flow, but the empirical coefficients are different. The total (turbulent and viscous) shear stress and total (turbulent and conductive) heat flux are constant throughout the channel. The locations of maximum root-mean-square streamwise velocity and temperature fluctuations are close to the walls, while the location of maximum root-mean-square spanwise and vertical velocity fluctuations are at the channel center. The correlation coefficients between velocities and temperature are fairly constant in the center core of the channel. In particular, the streamwise velocity is highly correlated with temperature (correlation coefficient ≈−0.9). At the channel center, the turbulence production is unable to counterbalance the dissipation, in which the diffusion terms (both turbulent and viscous) bring turbulent kinetic energy from the near-wall regions toward the channel center. The snapshots of the DNS database help explain the nature of the correlation coefficients. The elongated wall streaks for both streamwise velocity and temperature in the viscous sublayer are well simulated. Moreover, the current DNS shows organized large-scale eddies (secondary rotations) perpendicular to the direction of mean flow at the channel center.
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Karniadakis, George E., Bora B. Mikic, and Anthony T. Patera. "Minimum-dissipation transport enhancement by flow destabilization: Reynolds’ analogy revisited." Journal of Fluid Mechanics 192 (July 1988): 365–91. http://dx.doi.org/10.1017/s0022112088001909.
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A classical transport enhancement problem is concerned with increasing the heat transfer in a system while minimizing penalties associated with shear stress, pressure drop, and viscous dissipation. It is shown by Reynolds' analogy that viscous dissipation in a wide class of flows scales linearly with the Nusselt number and quadratically with the Reynolds number. It thus follows that transport enhancement optimization is equivalent to a problem in hydrodynamic stability theory; a more unstable flow will achieve the same Nusselt number at a lower Reynolds number, and therefore at a fraction of the dissipative cost. This transport-stability theory is illustrated in a numerical study of supercritical (unsteady) two-dimensional flow in an eddy-promoter channel comprising a plane channel with an infinite periodic array of cylindrical obstructions.It is shown that the addition of small cylinders to a plane channel results in stability modes that are little changed in form or frequency from plane-channel Tollmien-Schlichting waves. However, eddy-promoter flows are dramatically less stable than their plane-channel counterparts owing to cylinder-induced shear-layer instability (with critical Reynolds numbers on the order of hundreds rather than thousands), and thus these flows yield heat transfer rates commensurate with those of a plane-channel turbulent flow but at much lower Reynolds number. Small-cylinder supercritical eddy-promoter flows are shown to roughly preserve the convective-diffusive Reynolds analogy, and it thus follows from the transport-stability theory that eddy-promoter flows achieve the same heat transfer rates as plane-channel turbulent flows while incurring significantly less dissipation.
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Tutar, Mustafa, and Ali Karakus. "A numerical study of solidification and viscous dissipation effects on polymer melt flow in plane channels." Journal of Polymer Engineering 33, no. 2 (April 1, 2013): 95–110. http://dx.doi.org/10.1515/polyeng-2012-0060.
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Abstract The combined effects of solidification and viscous dissipation on the hydrodynamic and thermal behavior of polymer melt flow during the injection process in a straight plane channel of constant cross section are numerically studied by considering the shear-rate and temperature-dependent viscosity and transient-phase change behavior. A numerical finite volume method, in conjunction with a modified form of the Cross constitutive equation to account for shear rate, temperature-dependent viscosity changes and a slightly modified form of the method proposed by Voller and Prakash to account for solidification of the liquid phase, is used and a validation with an analytical solution is presented for viscous heating effects. The hydrodynamic and solidified layers growth under the influence of a transient phase-change process and viscous dissipation, are analyzed for a commercial polymer melt flow, polypropylene (PP) for different parametric conditions namely, inflow velocity, polymer injection (inflow) temperature, the channel wall temperature, and the channel height. The results demonstrate that the proposed numerical formulations, including conjugate effects of viscous heating and transient-solidification on the present thermal transport process, can provide an accurate and realistic representation of polymer melt flow behavior during the injection molding process in plane channels with less simplifying assumptions.
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Béthune, William, and Henrik Latter. "Electric heating and angular momentum transport in laminar models of protoplanetary discs." Monthly Notices of the Royal Astronomical Society 494, no. 4 (May 5, 2020): 6103–19. http://dx.doi.org/10.1093/mnras/staa908.
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ABSTRACT The vertical temperature structure of a protoplanetary disc bears on several processes relevant to planet formation, such as gas and dust grain chemistry, ice lines, and convection. The temperature profile is controlled by irradiation from the central star and by any internal source of heat such as might arise from gas accretion. We investigate the heat and angular momentum transport generated by the resistive dissipation of magnetic fields in laminar discs. We use local 1D simulations to obtain vertical temperature profiles for typical conditions in the inner disc (0.5–4 au). Using simple assumptions for the gas ionization and opacity, the heating and cooling rates are computed self-consistently in the framework of radiative non-ideal magnetohydrodynamics. We characterize steady solutions that are symmetric about the mid-plane and which may be associated with saturated Hall-shear unstable modes. We also examine the dissipation of electric currents driven by global accretion-ejection structures. In both cases we obtain significant heating for a sufficiently high opacity. Strong magnetic fields can induce an order-unity temperature increase in the disc mid-plane, a convectively unstable entropy profile, and a surface emissivity equivalent to a viscous heating of α ∼ 10−2. These results show how magnetic fields may drive efficient accretion and heating in weakly ionized discs where turbulence might be inefficient, at least for a range of radii and ages of the disc.
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Mortikov, Evgeny V., Andrey V. Glazunov, and Vasily N. Lykosov. "Numerical study of plane Couette flow: turbulence statistics and the structure of pressure–strain correlations." Russian Journal of Numerical Analysis and Mathematical Modelling 34, no. 2 (April 24, 2019): 119–32. http://dx.doi.org/10.1515/rnam-2019-0010.
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AbstractThe paper presents the results of direct numerical simulation of turbulent plane Couette flow. The calculations were performed for Reynolds numbers Re =U0H/ν(His the height of the channel, ±U0/2 is the motion velocities of the lower and upper walls, respectively,νis the kinematic viscosity) from 5200 (where viscous effects significantly affect the flow structure) to 80000 (where a logarithmic layer is clearly observed). Estimates of terms of the equation for the balance of turbulent Reynolds stresses are obtained, which indicate the importance of the kinetic energy transport by velocity fluctuations. The vertical transport of the turbulent momentum flux is less important and partly compensated by the transport of pressure fluctuations. It is shown that in the logarithmic layer the normal components of the ‘pressure–strain rate’ correlation tensor are described in the framework of the ‘isotropization of production’ model, and in the central part of the channel they are described by the linear Rotta model [29]. The additive model considering both the interaction of the velocity field fluctuation and the influence of the mean velocity gradient is a good approximation only for the off-diagonal component of the tensor entering the balance equation for the turbulent momentum flux.
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Eu, Byung Chan, Roger E. Khayat, Gert D. Billing, and Carl Nyeland. "Nonlinear transport coefficients and plane Couette flow of a viscous, heat-conducting gas between two plates at different temperatures." Canadian Journal of Physics 65, no. 9 (September 1, 1987): 1090–103. http://dx.doi.org/10.1139/p87-180.
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By using the example of plane Couette flow between two plates maintained at different temperatures, we present a method of calculating flow profiles for rarefied gases. In the method, generalized hydrodynamic equations are derived from the Boltzmann equation. They are then solved with boundary conditions calculated by taking into consideration the interfacial interaction between the surface and the gas molecule. The nonlinear transport coefficients employed in the generalized hydrodynamic equations are obtained from the Boltzmann equation by means of the modified-moment method. The profiles calculated are in agreement with the Liu–Lees theory as long as the boundary values are in agreement. It is found that the viscous-heating effect has a significant influence on the temperature and velocity profiles. The nonlinearity of transport coefficients also has significant effects on the profiles as the Knudsen and Mach numbers increase.
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da SILVA, C. B., and O. MÉTAIS. "On the influence of coherent structures upon interscale interactions in turbulent plane jets." Journal of Fluid Mechanics 473 (December 10, 2002): 103–45. http://dx.doi.org/10.1017/s0022112002002458.
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The influence of the coherent structures on grid/subgrid-scale (GS/SGS) interactions in free shear layers is analysed through the application of a top-hat filter to several plane jet direct numerical simulations (DNS). The Reynolds number based on the plane jet inlet slot width is Reh = 3000. The study deals with energy containing (Kelvin–Helmholtz) and inertial range (streamwise) vortices, from the far field of the turbulent plane jet. The most intense kinetic energy exchanges between GS and SGS occur near these structures and not randomly in the space. The GS kinetic energy is dominated by GS advection and GS pressure/velocity interactions which appear located next to the Kelvin–Helmholtz rollers. Surprisingly, GS/SGS transfer is not very well correlated with the coherent vortices and GS/SGS diffusion plays an important role in the local dynamics of both GS and SGS kinetic energy. The so-called ‘local equilibrium assumption’ holds globally but not locally as most viscous dissipation of SGS kinetic energy takes place within the vortex cores whereas forward and backward GS/SGS transfer occurs at quite different locations. Finally, it was shown that SGS kinetic energy advection may be locally large as compared to the other terms of the SGS kinetic energy transport equation.
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Somigliana, Alice, Claudia Toci, Giuseppe Lodato, Giovanni Rosotti, and Carlo F. Manara. "Effects of photoevaporation on protoplanetary disc ‘isochrones’." Monthly Notices of the Royal Astronomical Society 492, no. 1 (December 11, 2019): 1120–26. http://dx.doi.org/10.1093/mnras/stz3481.
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ABSTRACT Protoplanetary discs are the site of star and planet formation, and their evolution and consequent dispersal deeply affect the formation of planetary systems. In the standard scenario they evolve on time-scales ∼Myr due to the viscous transport of angular momentum. The analytical self-similar solution for their evolution predicts specific disc isochrones in the accretion rate–disc mass plane. However, photoevaporation by radiation emitted by the central star is likely to dominate the gas disc dispersal of the innermost region, introducing another (shorter) time-scale for this process. In this paper, we include the effect of internal (X and EUV) photoevaporation on the disc evolution, finding numerical solutions for a population of protoplanetary discs. Our models naturally reproduce the expected quick dispersal of the inner region of discs when their accretion rates match the rate of photoevaporative mass loss, in line with previous studies. We find that photoevaporation preferentially removes the lightest discs in the sample. The net result is that, counter-intuitively, photoevaporation increases the average disc mass in the sample, by dispersing the lightest discs. At the same time, photoevaporation also reduces the mass accretion rate by cutting the supply of material from the outer to the inner disc. In a purely viscous framework, this would be interpreted as the result of a longer viscous evolution, leading to an overestimate of the disc age. Our results thus show that photoevaporation is a necessary ingredient to include when interpreting observations of large disc samples with measured mass accretion rates and disc masses. Photoevaporation leaves a characteristic imprint on the shape of the isochrone. Accurate data of the accretion rate–disc mass plane in the low disc mass region therefore give clues on the typical photoevaporation rate.
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Chiodi, Filippo, Philippe Claudin, and Bruno Andreotti. "A two-phase flow model of sediment transport: transition from bedload to suspended load." Journal of Fluid Mechanics 755 (August 22, 2014): 561–81. http://dx.doi.org/10.1017/jfm.2014.422.
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AbstractThe transport of dense particles by a turbulent flow depends on two dimensionless numbers. Depending on the ratio of the shear velocity of the flow to the settling velocity of the particles (or the Rouse number), sediment transport takes place in a thin layer localized at the surface of the sediment bed (bedload) or over the whole water depth (suspended load). Moreover, depending on the sedimentation Reynolds number, the bedload layer is embedded in the viscous sublayer or is larger. We propose here a two-phase flow model able to describe both viscous and turbulent shear flows. Particle migration is described as resulting from normal stresses, but is limited by turbulent mixing and shear-induced diffusion of particles. Using this framework, we theoretically investigate the transition between bedload and suspended load.
Book chapters on the topic "Viscount (Transport plane)"
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Zaks, Michael A., and Alexander Nepomnyashchy. "Anomalous Transport in Steady Plane Viscous Flows: Simple Models." In Advances in Dynamics, Patterns, Cognition, 61–76. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-53673-6_5.
Full textConference papers on the topic "Viscount (Transport plane)"
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Ababneh, Mohammed T., Frank M. Gerner, Pramod Chamarthy, Peter de Bock, Shakti Chauhan, and Tao Deng. "Thermo-Fluid Model for High Thermal Conductivity Thermal Ground Planes." In ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/mnhmt2012-75185.
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The thermal ground plane (TGP) is an advanced planar heat pipe designed for cooling microelectronics in high gravitational fields. A thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). Viscous laminar flow pressure losses are predicted to determine the maximum heat load when the capillary limit is reached. This paper shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that the thermo-fluid model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP. The wick porosity plays an important effect on maximum heat transport capability. A large adverse gravitational field strongly decreases the maximum heat transport capability of the TGP. Axial effective thermal conductivity is mostly unaffected by the gravitational field. The maximum length of the TGP before reaching the capillary limit is inversely proportional to input power.
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Dalton, Charles, and Wu Zheng. "Numerical Solutions of a Viscous Uniform Approach Flow Past Square and Diamond Cylinders." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32287.
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Numerical results are presented for a uniform approach flow past square and diamond cylinders, with and without rounded corners, at Reynolds numbers of 250 and 1000. This unsteady viscous flow problem is formulated by the 2-D Navier-Stokes equations in vorticity and stream-function form on body-fitted coordinates and solved by a finite-difference method. Second-order Adams-Bashforth and central-difference schemes are used to discretize the vorticity transport equation while a third-order upwinding scheme is incorporated to represent the nonlinear convective terms. A grid generation technique is applied to provide an efficient mesh system for the flow. The elliptic partial differential equation for stream-function and vorticity in the transformed plane is solved by the multigrid iteration method. The Strouhal number and the average in-line force coefficients agree very well with the experimental and previous numerical values. The vortex structures and the evolution of vortex shedding are illustrated by vorticity contours. Rounding the corners of the square and diamond cylinders produced a noticeable decrease on the calculated drag and lift coefficients.
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Dennis, Kadeem, and Kamran Siddiqui. "Characterization of Thermals in a Heated Turbulent Boundary Layer." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5436.
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Abstract The hydrodynamic boundary layer encountered in many practical engineering systems is turbulent in nature and known to play a significant role in governing the induced friction drag and species transport. In turbulent boundary layer flows, heat transfer is often involved which increases flow complexity due to the influence of buoyancy. When the buoyant force is sufficiently large in magnitude, thermals carrying heated fluid are known to detach and rise from the wall. Literature review shows that in mixed convection, thermals have been primarily identified through qualitative flow visualizations and there is a scarcity of their quantitative assessment. Furthermore, the evolution of thermals in the boundary layer with respect to flow inertia and viscous shear is not well-understood. Hence, there is a need for a better understanding of the dynamics of thermals in mixed convection turbulent boundary layer flow. The objective of this study is to experimentally investigate the three-dimensional nature of thermals rising from a turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop low-disturbance wind tunnel with a test section featuring a 1 m long heated bottom wall. The multi-plane particle image velocimetry (PIV) technique was used to capture images in multiple planes with respect to the turbulent boundary layer mean flow direction for three-dimensional characterization. The measurements were conducted at Richardson numbers (Ri) of 0.3, 1.0, and 2.0. Flow visualization images are used to describe the nature of thermals and the dynamical processes involved during their interaction with bulk boundary layer flow. An image processing algorithm to detect thermals is then detailed and applied to experimental images. The performance of the new algorithm is then assessed in its ability to detect thermals.
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Rampazzo, Fabiano P., Marcio M. Tsukamoto, Luis A. Quadrante, Kazuo Nishimoto, Marcos Q. de Siqueira, Ricardo Franciss, and Felipe Rateiro Pereira. "Coupled Analysis of DP-Tugboat and Onshore Pre-Assembled SCR (Steel Catenary Riser) Transportation System." In ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/omae2008-57571.
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This paper presents the study of the dynamic behavior of an onshore pre-assembled 8" SCR (Steel Catenary Riser) being transported to the installation place by two tugboats with DP system. The system is composed by two tugboats similar to a Normand Neptun (LOA 80m and displacement of 4200t), one in front of the riser (Lead) and the other at the back of the riser (Trail) controlled by DP system to keep the trajectory for installation location. During the transportation, the system passes through 3 different configurations: Offbottom, BuoyCatenary and Catenary. Offbottom configuration is composed by many buoys (effective buoyancy of 30kN) and chains distributed along the riser to guarantee the relative distance between the riser and the seabed, independently of seabed irregularities. When the sea gets deeper, the riser assume the BuoyCatenary configuration, where the riser forms a catenary with buoys; when it achieves a water depth up to 500 meters, all the system buoy+chain are removed and the riser assume the form of a free catenary until it arrives at the installation place. Two approaches was used to evaluate transport analysis of a onshore pre-assembled SCR. In the first approach (uncoupled analysis), the transportation was simulated using the Anflex software to calculate the dynamic response of the line composed by beam elements, imposing, at the top of the riser, the tugboat motion obtained from spectral analysis. In the second approach (coupled analysis), the transport was simulated using the TPN software to calculate the dynamic motion of the tugboats considering the dynamic positioning system and the Anflex software to calculate the dynamic response of the lines. The main propose of this paper is show the necessity of do coupled analysis for the SCR transport. This study are focus in a parametric analysis of the tugboat viscous damping influence, that were performed (1, 5 and 10% of the critic damping), as well as the damping generated by the riser in the tugboat motion, the relative motion influence in risers tensions and the tugboat’s bollard pull.
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Bouscasse, Benjamin, Andrea Colagrossi, Salvatore Marrone, and Antonio Souto-Iglesias. "Viscous Flow Past a Circular Cylinder Below a Free Surface." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24488.
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Flow past a circular cylinder close to a free surface at low Reynolds and large Froude numbers is investigated numerically using the Smoothed Particle Hydrodynamics model. This meshless method allows for a non-diffusive computation of the free surface evolution, even while breaking and fragmentation may occur. The distance of the cylinder to the free surface, submergence, is varied in order to investigate the detached flow patterns dependence with this factor. Vorticity shed by the cylinder, vortex generation due to free surface breaking, mixing processes, and drag and lift coefficients behavior are discussed. It has been found that, for small submergences, the classical Von Karman vortex shedding from the cylinder does not take place. In turn, moderate vortex shedding occurs, departing not from the cylinder but from vorticity generated at the free surface. This shedding takes places simultaneously with the transport of free surface fluid elements into the bulk of the fluid. It has been also found that for even smaller depth ratios, a vorticity layer remains spatially localized between the cylinder and the free surface, and a stagnation recirculating area develops behind the cylinder. Results are compared with literature finding reasonable qualitatively agreement with experimental works conducted with similar geometrical configuration but larger Reynolds number.
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Champmartin, Ste´phane, Abdlehak Ambari, and Abderrahim Ben Richou. "Kinematics of a Free Particle Moving Between Two Parallel Walls." In ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels collocated with 3rd Joint US-European Fluids Engineering Summer Meeting. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30502.
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The understanding of some physical phenomena involved in the transport of free particles such as fibers during injection processes is an important issue. To answer some of the questions arising in such problems, we study here numerically the quasi-steady kinematics of a free cylindrical solid particle moving in a Newtonian fluid confined between two parallel plane walls taking the hydrodynamic interactions into account. This is achieved by the use of the resistance matrix technique relating the kinematics of the particle to the forces and the torques exerted on the particle and to the dissipation induced by the motion of this particle. Our approach is confirmed by asymptotical developments and by a comparison with other authors in some cases. The solutions of three practical problems are given. In the first one, the sedimentation of the particle is studied. It is found that the maximum settling velocity of the free particle is obtained at a position off the symmetry plane. The cylinder is observed to rotate counter intuitively against the direction of rolling along the adjacent wall. Moreover the angular velocity has an influence on the settling velocity when the concentration is very high. The second problem concerns the transport of a neutrally buoyant cylindrical particle in a Poiseuille flow. This study reveals that there are relative translational and angular velocities between the free particle and the undisturbed fluid particle contrary to the commonly admitted hypothesis used in several models and numerical codes. Finally the third problem is a combination of the two previous situations: the transport of a non-neutrally buoyant particle in a Poiseuille flow. Depending on the ratio of the buoyancy forces to the viscous ones, different solutions are possible and exposed. Other problems can also be solved with this approach which is less time-consuming than complex methods such as DNS.
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Ho, Y. H., and B. Lakshminarayana. "Computation of Unsteady Viscous Flow Through Turbomachinery Blade Row due to Upstream Rotor Wakes." In ASME 1993 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1993. http://dx.doi.org/10.1115/93-gt-321.
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A time-accurate, two-dimensional, pressure-based, Navier-Stokes solver for incompressible flow is developed and used to carry out the numerical simulation of rotor-stator interaction. A low Reynolds number form of the two-equation turbulence model is used to account for the turbulence effects. In order to improve the accuracy of the numerical scheme, a central differencing plus an artificial dissipation scheme is implemented to provide precise control of numerical dissipation. An inner loop iteration scheme is used at each time step to account for the non-linear effects. The computation of unsteady flow through a flat plate cascade subjected to a transverse gust reveals that the choice of grid spacing and the amount of artificial dissipation is critical for accurate prediction of unsteady phenomena. The rotor-stator interaction problem is simulated by starting the computation upstream of the stator, and the upstream rotor wake is specified from the experimental data. The results show that the stator potential effects have appreciable influence on the upstream rotor wake. The predicted unsteady wake profiles are compared with the available experimental data and the agreement is good. The numerical results are interpreted to draw conclusions on the unsteady wake transport mechanism in the blade passage.
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Mansour, Mahmoud L., John Gunaraj, and Shraman Goswami. "Validation of Steady Average-Passage and Mixing Plane CFD Approaches for the Performance Prediction of a Modern Gas Turbine Multistage Axial Compressor." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50653.
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This paper summarizes the results of a validation and calibration study for two modern Computational Fluid Dynamics programs that are capable of modeling multistage axial compressors in a multi-blade row environment. The validation test case is a modern 4-stage high pressure ratio axial compressor designed and tested by Honeywell Aerospace in the late 90’s. The two CFD programs employ two different techniques for simulating the steady three-dimensional viscous flow field in a multistage/multiblade row turbo-machine. The first code, APNASA, was developed by NASA Glenn Research Center “GRC” and applies the approach by Adamczyk [1] for solving the average-passage equations which is a time and passage-averaged version of the Reynolds Averaged Navier Stokes (RANS) equations. The second CFD code is commercially marketed by ANSYS-CFX and applies a much simpler approach, known as the mixing-plane model, for combining the relative and the stationary frames of reference in a single steady 3D viscous simulation. Results from the two CFD programs are compared against the tested compressor’s overall performance data and against measured flow profiles at the leading edge of the fourth stator. The paper also presents a turbulence modeling sensitivity study aimed at documenting the sensitivity of the prediction of the flow field of such compressors to use of different turbulence closures such as the standard K-ε model, the Wilcox K-ω model and the Shear-Stress-Transport K-ω/SST turbulence model. The paper also presents results that demonstrate the CFD prediction sensitivity to modeling the compressor’s hub leakages from the inner-banded stator cavities. Comparison to the test data, using the K-ε turbulence closure, show that APNASA provides better accuracy in predicting the absolute levels of the performance characteristics. The presented results also show that better predictions by CFX can be obtained using the K-ω and the SST turbulence models. Modeling of the hub leakage flow was found to have significant and more than expected impact on the compressor predicted overall performance. The authors recommend further validation and evaluation for the modeling of the hub leakage flow to ensure realistic predictions for turbo-machinery performance.
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Ahmed, Saad A., and Kamorudeen B. Abidogun. "Turbulence Characteristics in an Axisymmetric Sudden Expansion." In ASME 1997 Turbo Asia Conference. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-aa-012.
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Simultaneous two-component laser Doppler velocimeter measurements were made in an axisymmetric sudden expansion to measure the flow properties of a confined, isothermal flowfield of a research dump combustor. Measurements of mean velocities, Reynolds stresses, and triple products were carried out at axial distances ranging from 0.38H (H = step height) to 18H downstream of the dump plane. Detailed experimental data are provided to help in the understanding of the behavior of turbulent transport characteristics of a confined shear layer. In addition, the data from this study will be available for upgrading / or evaluating advanced numerical codes used to predict complex turbulent flows. The turbulent kinetic energy terms: convection, diffusion, and production terms were computed directly from the experimental data using central difference, while the viscous dissipation term was obtained from balance of energy equation. The results indicate that the shear layer flow created by the sudden expansion enhances the combustor performance by serving as a turbulence generator mechanism.
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Murari, Sridhar, Sunnam Sathish, Ramakumar Bommisetty, and Jong S. Liu. "CFD Analyses of a Single Stage Turbine With Inlet Hot-Streak at Different Circumferential Locations." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94141.
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This paper presents a detailed flow and heat transfer characteristic analysis on a gas turbine first stage under hot-streak inlet conditions. Simulations were performed for two locations of hot-streak at turbine inlet with respect to the first stage vane, i.e. i) passage center and ii) blade center. The two kinds of inlet conditions have the same mass-averaged total temperature and total pressure. The passage center hot-streak total pressure and total temperature contours are obtained from the rig data published by Butler. Linear interpolation technique is used to move the hot-streak location from passage center to blade center. The ratio of highest temperature in hot-streak to free stream temperature is 2.0. Mixing plane (MP) and Non-linear harmonic (NLH) approaches are used to address the data transport across the rotor-stator station interface. The numerical solution is validated with the test data obtained from the published rig tests. NLH approach predicted the rotor blade surface temperature distributions close to rig data with a percentage deviation of 3%. The change in hot-streak circumferential position from blade center to passage center lead to decreased attenuation of hot-streak due to pronounced cross momentum transport of fluid across the viscous layers. Turbine flow with blade center hot-streak experiences transient periodic fluctuation of heat load on rotor surface. High temperature gradients are observed at turbine exit station with passage center hot-streak.