Viscous Compressible Heat-conducting Gas Research Articles

PARALLEL COMPUTATIONS IN STUDIES OF DEPENDENCE OF GAS DYNAMIC PARAMETERS OF UPWARD SWIRLING FLOW OF GAS ON BLOWING VELOCITY

The rectangular parallelepiped explicit difference schemes for the numerical solution of the complete built system of Navier-Stokes equations. These solutions describe the three-dimensional flow of a compressible viscous heat-conducting gas in a rising swirling flows, provided the forces of gravity and Coriolis. This assumes constancy of the coefficient of viscosity and thermal conductivity. The initial conditions are the features that are the exact analytical solution of the complete Navier-Stokes equations. Propose specific boundary conditions under which the upward flow of gas is modeled by blowing through the square hole in the upper surface of the computational domain. A variant of parallelization algorithm for calculating gas dynamic and energy characteristics. The results of calculations of gasdynamic parameters dependency on the speed of the vertical blowing by the time the flow of a steady state flow.

ACCOUNTING INFLUENCE OF CENTRIFUGAL FORCE IN THE NUMERICAL MODELING OF RISING SWIRLED GAS FLOW

In work the consistent inclusion of centrifugal force in the numerical calculations of three-dimensional gas-dynamic characteristics of the unsteady flow of compressible viscous heat-conducting gas in an upward swirling flow caused by the vertical cold blowing. Provides detailed conversion of the complete system of Navier-Stokes equations associated with consistent view of the centrifugal force. Results of thermodynamic calculations and comparisons, speed and power characteristics of emerging upward swirling flows. There was a slight influence of the centrifugal force on the basic parameters of the gas-dynamic study of complex flows of gas.

NUMERICAL CALCULATION OF CONVECTIVE FLOW OF GAS AT CIRCULAR-TYPE SCHEME OF HEATING

To investigate the convective flows of polytropic gas a complete system of Navier - Stokes equations is consid-ered. As the initial and boundary conditions the specific ratios are offered. The proposed initial and boundary condi-tions realization is carried out at construction of the numerical solution of the complete system of Navier - Stokes equations for modeling the unsteady state three-dimensional convection flows of the compressible viscous heat-conducting gas in the isolated cubic area. Three components of the velocity vector are calculated for the initial stage of the convective flow. It is shown that the velocity components are complex and depend essentially on the heating shape, height and time.

ASYMPTOTIC BEHAVIOR OF THE MOTION OF A VISCOUS HEAT-CONDUCTING ONE-DIMENSIONAL GAS WITH RADIATION: THE PURE SCATTERING CASE

We study the large-time behavior of the solution of an initial-boundary value problem for the equations of 1D motions of a compressible viscous heat-conducting gas coupled with radiation through a radiative transfer equation. Assuming only scattering processes between matter and photons (neglecting absorption and emission) and suitable hypotheses on the transport coefficients, we prove that the unique weak solution of the problem converges toward the static state.

Physical and mathematical modeling of a supersonic flow around a cylinder with a porous insert

Results of numerical and experimental modeling of a supersonic flow (M∞ = 4.85) around a model of a streamwise-aligned cylinder with a cellular-porous insert permeable for the gas on the frontal face of the cylinder are described. Experimental data on the influence of the pore structure and the length of the porous cylindrical insert on the model drag, pressure on the frontal face of the cylinder, and flow pattern are obtained. Numerical modeling includes solving Favre-averaged Navier-Stokes equations, which describe the motion of a viscous compressible heat-conducting gas. The system is supplemented with a source term taking into account the drag of the porous body within the framework of the continuum model of filtration. Data on pressure and velocity fields inside the porous body are obtained in calculations, and the shape of an effective pointed body whose drag is equal to the drag of the model considered is determined. The calculated results are compared with the measured data and schlieren visualization of the flow field.

Large-time behavior of the motion of a viscous heat-conducting one-dimensional gas coupled to radiation

We study the large-time behavior of the solution of an initial-boundary value problem for the equations of 1D motions of a compressible viscous heat-conducting gas coupled to radiation through a radiative transfer equation. Assuming suitable hypotheses on the transport coefficients and adapted boundary conditions, we prove that the unique strong solution of this problem converges toward a well-determined equilibrium state at exponential rate.

Global existence of solutions for the one-dimensional motions of a compressible viscous gas with radiation: An “infrarelativistic model”

We consider an initial–boundary value problem for the equations of 1D motions of a compressible viscous heat-conducting gas coupled with radiation through a radiative transfer equation. Assuming suitable hypotheses on the transport coefficients, we prove that the problem admits a unique weak solution.

Splitting algorithms as applied to the Navier-Stokes equations

Implicit finite-difference schemes of approximate factorization and predictor-corrector schemes based on a special splitting of operators are proposed for the numerical solution of the Navier-Stokes equations governing a viscous compressible heat-conducting gas. The schemes are based on scalar tridiagonal Gaussian elimination and are unconditionally stable. The accuracy and efficiency of the algorithms are confirmed by computing two-dimensional flows of complex geometry.

Modeling of supersonic flows near flying vehicle elements

Supersonic flows near flying vehicle elements are calculated in the approximation of the full Navier-Stokes equations for a viscous compressible heat-conducting gas with different values of free-stream. Mach and Reynolds numbers and angles of attack. The main laws of the flow near the lifting surface. and in the inlet are obtained.

Formation of a vortex flow at the laser cutting of sheet metal with low pressure of assisting gas

Specific features of subsonic jet gas flows in narrow channels geometrically similar to the laser cut are studied experimentally and theoretically. Such flows are visualized by a technique based on prior application of a viscous liquid film onto the side walls of the channel made of transparent glass. The gas flow inside the channel induces a liquid flow on the glass wall in the form of extremely small filaments, which coincide with the streamlines of the gas flow. Filming of these filaments by a CCD camera allows one to capture the specific features of these gas-dynamic flows. Mathematical modelling of the dynamics of a viscous compressible heat-conducting gas was performed by solving full three-dimensional Navier–Stokes equations. Numerical calculations and experiments reveal vortex structures in the flow at the entrance and exit of the channel, which may directly affect the surface quality in real gas-laser cutting of metals. The largest vortex, which arises at the channel exit, collects and accumulates the liquid flowing down the channel walls. Jet flows are generated by sonic nozzles with conical or cylindrical exit sections or by a double coaxial nozzle. The double nozzle includes the central conical nozzle and the side concentric nozzle, which allows additional side injection of the gas to be organized. The study with the double nozzle shows that the vortices disappear as the pressure in the external nozzle is increased, and a stable vortex-free attached gas flow is formed.

Rayleigh–Bénard flow of a rarefied gas and its attractors. II. Chaotic and periodic convective regimes

This second part of our study of the Rayleigh–Bénard flow of a rarefied gas deals with the analysis of the convection regimes for near-continuum conditions at a Knudsen number Kn=0.001. Here a set of qualitatively new regimes and final states have been found for different Froude (Fr) numbers and a fixed temperature ratio Tc/Th=0.1. In contrast to paper I [Phys. Fluids 14, 2255 (2002)] where we were mainly interested in the long time behavior, or, in other words, in the flow attractors, in this paper we extend the analysis of the most interesting cases to the full transition period from the initial state to the established flow regime. Two transient periods (to a chaotic attractor found for Fr=1.0 and to a stable two-roll configuration for Fr=2.0) are computed by using two different approaches: a direct simulation Monte Carlo method (molecular approach) and a finite difference method solving the system of equations for a compressible viscous heat-conducting gas (continuum approach). The comparison of the spatiotemporal structures shows that both approaches exhibit the basic properties of the transition to a chaotic fluid motion.

Generation of High-Frequency Harmonics in the Case of Large-Amplitude Vibrations of a Gas in a Closed Tube

Based on the model of a viscous compressible heat-conducting gas, the author investigates numerically the vibrations of a gas column in a closed tube in excitation by a flat piston that moves according to a harmonic law with an amplitude comparable to the resonator length. Consideration is given to the process of transformation of the mode and frequency of vibrations of the gas column for a fixed excitation frequency; the transformation is accompanied by a change of the type of resonance and is related to the increase in the eigenfrequency of the system due to the increase in the average temperature of the gas.

A numerical study of the flow in the wake of a plate of finite thickness

We give a numerical study of the flow near the backside of a plate of finite thickness past which a supersonic flow of viscous compressible heat-conducting gas is occurring, as a function of the Reynolds number, symmetry conditions, and temperature conditions on the surface. Thirteen figures. Bibliography: 7 titles.

Flow around the afterbody of a plate in a longitudinal gas stream with transverse injection from the lateral surface

The flow around the afterbody of a plate of finite thickness in a supersonic gas stream is investigated on the basis of a numerical solution of the time-dependent Navier-Stokes equations for a compressible viscous heat-conducting gas. The change in the flow pattern with the onset of transverse slot injection from the body surface in the vicinity of the base section is studied. For constant supersonic injection, both steady and unsteady flow regimes could be obtained depending on the values of certain relevant parameters.

Flow separation structure in a nonstationary viscous gas flowing over a body

This paper studies the structure of the nonstationary pulsating flow of a viscous compressible heat-conducting gas flowing over a cylinder with a cylindrical step projection on its front end. In a stationary incident stream, a projecting step usually produces a separated vortex flow. In a pulsating incident stream, the overall flow structure, and the structure of the separated flow in particular, changes depending on the frequency and the amplitude of pulsations, and this change substantially affects the aerodynamic characteristics of the immersed body. Such nonstationary processes have been studied by numerical solution of two-dimensional nonstationary Navier-Stokes equations using an implicit iterative difference scheme [1], which approximates the original systems of equations with second-order accuracy in space and in time.

Numerical modeling of viscous separated flow in the near wake

The present paper studies laminar flow in the near wake behind a short blunt body. We have obtained the dependence on the Mach number and Reynolds number of the incident stream of a number of geometrical characteristics of the wake, the relative base pressure, and its contribution to the total body drag. Examples are given of the influence of body shape and its surface thermal regime on the base pressure. It has been observed that for some incident stream parameters fine-scale vortices form near the separation point (an analogous phenomenon has been mentioned earlier in individual experimental studies), and a local supersonic zone can occur on the axis of symmetry in the reverse flow. i. Formulation of the Problem and Method of Solution. We consider flow about an axisymmetric body with a vertical base truncation. A uniform supersonic stream of viscous compressible heat-conducting gas flows over the body at zero angle of attack. In accordance with theoretical ideas and on the basis of the available test data (see, e.g., [i, 3]) we can give the following scheme for the separated flow in the near wake. Under the influence of inertia forces, which predominate over the viscous forces, the boundary layer leaving the body separates from the body corner at the point G (Fig. i), located somewhat below the corner point F. The separated viscous layer entrains part of the gas occupying the wake region, thereby lowering the pressure there, and together with the external stream it is deviated toward the axis, where at some distance from the base rim it merges with the symmetric viscous layer, forming the wake throat. In the merge zone the base pressure increases, the flow is turned again (almost parallel to the axis), and a tail shock forms. The internal part of the viscous layer, close to the axis, losing speed due to interaction with the gas from the separated region, cannot overcome the increased pressure in the wake throat, and turns back toward the base of the body, and in the established near wake there forms a closed region of recirculating flow, separated from the rest of the flow by the dividing streamline GH. In the external inviscid flow there is flow expansion in the vicinity of the corner point F; immediately beyond the fan of expansion waves there is a stern shock wave, due to re-expansion of the wall viscous layer at the corner point. (Figure 1 also shows stream lines and pressure profiles obtained in one of the computations, and in these one can see the location of the tail shock.)

Effect of supersonic stream parameters on the characteristic time of transient step flow

There have been many studies of viscous compressible gas flow in wakes and behind steps [1–6] in which attention has been focused on the steady-state flow regime. The problem of the supersonic flow of a viscous compressible heat-conducting gas past a plain backward-facing step is considered. The problem is solved numerically within the framework of the complete system of Navier-Stokes equations. The passage of the solution from the initial data to the steady-state regime and the effect of the gas dynamic parameters of the external flow on the characteristic flow stabilization time are investigated.

Supersonic gas flow over a wavy surface

Exact numerical solutions of the problem are obtained for a compressible viscous heat-conducting gas flowing over a slightly wavy surface. The effect of the free-stream parameters on the stresses, the temperature fields and the heat fluxes at the wavy interface is studied in detail.

A moving-grids difference scheme for solving the equations of a viscous gas

FOR THE numerical solution of the equations of a viscous compressible heat-conducting gas, written in orthogonal coordinates, a conditionally stable difference scheme is presented, which is based on splitting the equations with respect to the physical processes and spatial directions. Moving difference grids constructed on the variational principle are used to increase the accuracy of the calculations.