Flow and Heat Transfer in Underexpanded Air Jets Issuing from the Sonic Nozzle of a Plasma Generator

We present the results of an experimental investigation and numerical simulation of the gasdynamic structure of underexpanded dissociated-air jets and the heat transfer in these strongly nonequilibrium flows under the test conditions realized in the 100-kW electrodeless VGU-4 plasma generator of the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS). The flow and heat transfer analysis is carried out on the basis of measurements of the static pressure in the plenum chamber, at the sonic nozzle exit, and on the low-pressure chamber wall, the stagnation pressure on the jet axis using a Pitot tube, and the heat transfer at the stagnation points of water-cooled models placed along the jet axis. The numerical simulation, based on complete Navier-Stokes equations, includes the calculation of (1) equilibrium air plasma flows in the discharge channel of the VGU-4 plasma generator; (2) underexpanded nonequilibrium dissociated-air jet outflow into the ambient space; and (3) axisymmetric jet flow past cylindrical models.     

群沙射流结构的实验研究

本文以90－150μm的标准细沙为研究对象，利用超声波速度剖面测量仪和数码摄录机进行了垂直入水群沙射流的实验研究，给出了的群沙入水后的运动规律。我们发现，群沙湍射入水的一霎那，底部瞬时产生反射波，由它带动的流速与群沙入水带动的流速同量级。     

Some Features of a Turbulent Separated Flow and Heat Transfer Behind a Step and a Rib. 1. Flow Structure

The influence of the shape and size of the obstacle on separated flow and heat transfer is studied experimentally. Results of investigation and comparative analysis of the hydrodynamic structure of a separated flow behind a step and a rib are presented. A principally different character of transfer processes in the separated flow behind obstacles of these types is demonstrated. The flow structure in the secondary vortex region is considered.     

LES of Jets in Cross Flow and Its Application to a Gas Turbine Burner

LES computations of jets in cross flow (JICF) were performed. Experimental investigations reported in literature are reproduced with good agreement concerning the momentum field and the mixing of a passive scalar. The results validate the ability of the present LES approach to compute fuel injection of the type JICF. LES computations of fuel injection in an industrial gas turbine burner are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical Simulation of a Supersonic Flow with Transverse Injection of Jets

A plane supersonic flow with symmetric perpendicular injection of jets through slots in the walls is numerically simulated with the use of Navier–Stokes equations. The effect of the jet pressure ratio and Mach number on the flow structure is considered. The angle of inclination of the shock wave and the separationregion length are found as functions of the jet pressure ratio. The influence of the jet pressure ratio on the increase in the lift force arising owing to interaction of the flow with the injected jet is found.     

Some Features of a Turbulent Separated Flow and Heat Transfer Behind a Step and a Rib. 2. Heat Transfer in a Separated Flow

Results of an experimental study of heat transfer in a separated flow behind a step and a rib are presented. The influence of the obstacle height (H = 6–30 mm) on heat and mass transfer and the structure of the thermal boundary layer is studied. The features of heat transfer in recirculation and relaxation zones of the separated flow are analyzed, and the effect of separation on intensification and suppression of turbulent heat transfer is determined.     

Vortex in a Supersonic Flow and its Influence on Blunt Body Flow and Heat Transfer

The dissipation of a tip vortex generated by a rectangular wing and the stagnation pressure and temperature distributions within the vortex are experimentally investigated. The interaction of the vortex with the bow shock ahead of a sphere and the heat flux distribution over the spherical surface are studied. The experiments were carried out at the Mach number M=3 and the unit Reynolds numbers Re₁=1.1·10⁷ and 3.7·10⁷ 1/m.     

Mass Transfer on a Delta Wing in a Hypersonic Flow

The effect of mass transfer on the parameters of the laminar boundary layer flow on a cold delta wing in a hypersonic viscous perfect-gas flow is investigated for the case of a strong viscous-inviscid interaction regime. The influence of the mass transfer intensity on the supercritical-subcritical transition coordinate and the local and total aerodynamic parameters of a delta wing with a power-law cross-section is numerically determined.     

Flow Structures Associated with Turbulent Mixing Noise and Screech Tones in Axisymmetric Jets

A jet from an axisymmetric convergent nozzle is studied at ideal and underexpanded conditions using velocity and acoustic data. Two particle imaging velocimetry setups, a 10 kHz system and a multi-camera configuration, were used to capture near-field velocities while simultaneously sampled with far-field microphones. Proper orthogonal decomposition is performed on the velocity data to extract modes representative of physical processes in the flow. The decomposed velocity fields are then correlated with acoustic data to identify modes related to specific noise spectra. Specifically, four modes are associated with noise production in the sonic plume. Selective flow-field reconstruction is carried out, revealing interesting dynamics associated with loud flow states. In the supersonic case, screech-containing and turbulent mixing modes are isolated. The spatial modes of each data set are then compared for similarities in structures.     

Heat Transfer in Supersonic Low-Re Flow Past a Sphere and a Cylinder

Supersonic perfect-gas flow past a sphere and a cylinder at a constant surface temperature is investigated on the basis of a numerical solution of the Navier-Stokes equations. The Re-dependence of the Nusselt number and the recovery coefficient is calculated for the Reynolds numbers ranging from 1 to 1000 and Mach numbers 3 (cylinder) and 5 (sphere) and compared with the experimental data. The influence of slip and no-slip conditions imposed on the body surface on the heat transfer parameters and the base flow is analyzed.     

Intensification of Heat Transfer in a Downward Liquid-Film Flow

Heat transfer in a film flow of the FC-72 dielectric liquid down a vertical surface with an embedded 150×150 mm heater is experimentally examined in the range of Reynolds numbers Re = 5–375. A chart of liquid-film flow modes is constructed, and characteristic heat-transfer regions are identified. Data on the dependence of heater-wall temperature and local heat flux at the axis of symmetry of the heater on the longitudinal coordinate are obtained. Local and mean heat-transfer coefficients are calculated. It is shown that enhanced heat transfer is observed in the region where rivulets starts forming in the low-Reynolds-number liquid-film flow.     

Generalized Plain Couette Flow and Heat Transfer in a Composite Channel

An analytical study of fluid flow and heat transfer in a composite channel is presented. The channel walls are maintained at different constant temperatures in such a way that the temperatures do not allow for free convection. The upper plate is considered to be moving and the lower plate is fixed. The flow is modeled using Darcy–Lapwood–Brinkman equation. The viscous and Darcy dissipation terms are included in the energy equation. By applying suitable matching and boundary conditions, an exact solution has been obtained for the velocity and temperature distributions in the two regions of the composite channel. The effects of various parameters such as the porous medium parameter, viscosity ratio, height ratio, conductivity ratio, Eckert number, and Prandtl number on the velocity and temperature fields are presented graphically and discussed.     

Calculation of Radiation Heat Transfer in Problems of Flow past Bodies with Account for Heat-Shield Coating Mass Loss

Flow past bodies with account for radiation heat transfer near the body nose is considered in connection with the problem of thermal protection of spacecraft entering planetary atmospheres. An approach based on the spherical harmonics method is used for taking radiation into account. The heating and ablation of the heat-shield coating is determined by numerically solving the heat conduction equation with a moving boundary. The thermal problem is solved together with the calculation of the vehicle trajectory, which makes it possible to estimate the effect of the coating mass loss on the trajectory parameters. The approach formulated is realized under the conditions of entry of a spherical segment and a spherically-blunted cone with equal mid-section radii into the Venusian atmosphere. Comparing the results makes it possible to choose the vehicle shape optimal with respect to the thermal regime.     

Effect of a Dispersed Admixture on the Flow Pattern and Heat Transfer in a Supersonic Dusty-Gas Flow Around a Cylinder

A mathematical model of two-phase (gas-solid particle) flow which takes into account particle-particle collisions and the feedback effect of the admixture on the gas parameters is proposed. The dispersed phase is described by a kinetic equation of the Boltzmann type and the carrier gas by modified Navier-Stokes equations. Using this model, a supersonic uniform dusty-gas flow past a cylinder is calculated. The fields of the macroparameters of the admixture and the carrier medium are obtained. The dependence of the heat transfer at the stagnation point on the relative particle size and the free-stream admixture concentration is studied in detail. The ranges of these parameters on which particle collisions and the feedback effect of the admixture on the carrier-gas flow are important are found.     

Flow in a Porous Matrix with Anisotropic Structure

The flow of a viscous fluid through a porous matrix undergoing only infinitesimal deformation is described in terms of intrinsic variables, namely, the density, velocity and stress occurring in coherent elements of each material. This formulation arises naturally when macroscopic interfaces are conceptually partitioned into area fractions of fluid–fluid, fluid–solid, and solid–solid contact. Such theory has been shown to yield consistent jump conditions of mass, momentum and energy across discontinuities, either internal or an external boundary, unlike the standard mixture theory jump conditions. In the previous formulation, the matrix structure has been considered isotropic; that is, the area fractions are independent of the interface orientation. Here, that is not assumed, so in particular, the cross-section area of a continuous fluid tube depends on its orientation, which influences the directional fluxes, and in turn the directional permeability, anisotropy of the structure. The simplifications for slow viscous flow are examined, and particularly for an isotropic linearly elastic matrix in which area partitioning induces anisotropic elastic response of the mixture. A final specialization to an incompressible fluid and stationary matrix leads to potential flow, and a simple plane flow solution is presented to illustrate the effects of anisotropic permeability.     

Vertical Momentum Transfer Induced by Internal Waves in a Two-Dimensional Flow

Fluid Dynamics - Free internal waves in a two-dimensional vertically inhomogeneous stratified flow are considered in the Boussinesq approximation with account of the Earth’s rotation. The...     

Analysis of Laminar Flow and Forced Convection Heat Transfer in a Porous Medium

The flow of an incompressible Newtonian fluid confined in a planar geometry with different wall temperatures filled with a homogenous and isotropic porous medium is analyzed in terms of determining the unsteady state and steady state velocities, the temperature and the entropy generation rate as function of the pressure drop, the Darcy number, and the Brinkman number. The one-dimensional approximate equation in the rectangular Cartesian coordinates governing the flow of a Newtonian fluid through porous medium is derived by accounting for the order of magnitude of terms as well as accompanying approximations to the full-blown three-dimensional equations by using scaling arguments. The one-dimensional approximate energy and the entropy equations with the viscous dissipation consisting of the velocity gradient and the square of velocity are derived by following the same procedure used in the derivation of velocity expressions. The one-dimensional approximate equations for the velocity, the temperature, and the entropy generation rate are analytically solved to determine the velocity, the temperature, and the entropy distributions in the saturated porous medium as functions of the effective process parameters. It is found that the pressure drop, the Darcy number, and the Brinkman number affect the temperature distribution in the similar way, and besides the above parameters, the irreversibility distribution ratio also affects the entropy generation rate in the similar way.     

Numerical Simulation of Turbulent Flow and Heat Transfer in a Three-Dimensional Channel Coupled with Flow Through Porous Structures

This study investigates numerically the turbulent flow and heat transfer characteristics of a T-junction mixing, where a porous media flow is vertically discharged in a 3D fully developed channel flow. The fluid equations for the porous medium are solved in a pore structure level using an Speziale, Sarkar and Gatski turbulence model and validated with open literature data. Overall, two types of porous structures, consisted of square pores, are investigated over a wide range of Reynolds numbers: an in-line and a staggered pore structure arrangement. The flow patterns, including the reattachment length in the channel, the velocity field inside the porous medium as well as the fluctuation velocity at the interface, are found to be strongly affected by the velocity ratio between the transversely interacting flow streams. In addition, the heat transfer examination of the flow domain reveals that the temperature distribution in the porous structure is more uniform for the staggered array. The local heat transfer distributions inside the porous structure are also studied, and the general heat transfer rates are correlated in terms of area-averaged Nusselt number accounting for the effects of Reynolds number, velocity ratio as well as the geometrical arrangement of the porous structures.