Quasigasdynamic Research Articles

Direct Simulation of Laminar–Turbulent Transition in a Viscous Compressible Gas Layer

We present simulation results for oscillatory modes in supersonic flow past an aircraft with a hypersonic jet engine. The flow of viscous compressible gas is modeled by a quasi-gas dynamic (QGD) system of equations. A coordinate transformation is applied to adapt the computational region to the configuration of the compression shock in supersonic flow past an object. An original method is proposed for the introduction of additional dissipation that smooths the instability in the neighborhood of the compression shock. The spectral characteristics of the oscillatory flow in the turbulence region follow the Kolmogorov law of oscillation energy decrease with increasing oscillation frequency.

Numerical simulation of the continuous media problems on hybrid computer systems

The paper presents some results of modeling continuous media problems on computer system with hybrid architecture on the base of Quasi Gas Dynamic (QGD) equations system. The successful experience in solving a wide variety of gas dynamic problems by means of QGD based schemes showed that they describe viscous heat conducting flows as good as schemes for Navier-Stokes equations, where the latter are applicable. The explicit scheme described here has a Courant stability condition even for very low Mach numbers. So, it is very convenient for computer systems with the hybrid architecture, in particular for GPU-based computers. Parallel realization is based on shmem programming technology. The calculations results show good parallelization efficiency.

Equations of stochastic quasi-gas dynamics: Viscous gas case

The article reports some results of test calculations of one model from the hierarchical set of models of gas dynamics obtained (a brief scheme of the deduction is presented) from a system of stochastic differential equations describing gas at moderate and small Knudsen numbers.

Parallel software package for simulation of continuum mechanics problems on modern multiprocessor systems

A parallel software package designed for numerical simulation of continuum mechanics problems is presented. In order to illustrate the capabilities of the package, two problems on simulation of supersonic gas flows, around a descent space vehicle and in the vicinity of a micro nozzle, were chosen. A system of equations of quasi-gas dynamics was used as a mathematical model for the dynamics of gas. Inasmuch as radiation transfer in gas is taken into account in the first problem, the multigroup approach and diffusion approximation are employed to describe radiation processes. The numerical algorithm is based on explicit in time finite volume schemes using nonregular locally condensed grids of different types. Parallel implementation of numerical schemes was executed in the context of the MPI+OpenMP technology and optimized for computations performed by means of modern clusters with hybrid architecture.

Equations of quasi-gas dynamics

Based on a system of stochastic differential equations describing gas for small Knudsen numbers, equations of gas dynamics with additional small terms for the simplest Fokker-Planck model of the Boltzmann collision integral are obtained in an explicit form.

Calculation of gas flow parameters around a reentry vehicle

An original numerical algorithm for calculating the gas parameters around a reentry vehicle was described and tested. It is based on a system of Quasi Gas Dynamics (QGD) equations and its approximations on hybrid meshes, which suppose adaptive, locally thickening meshes including both rectangular and triangular cells. The results of the calculations on a sequence of condensed meshes for Mach number values of 2, 5, and 12 are presented. These results correspond to well-known data and demonstrate the high efficiency of the algorithm.

Simulating Argon, Helium, and Nitrogen Shock Waves

We simulate the structure of the shock wave front in the range of Mach numbers from 1.5 to 10 using quasigasdynamic (QGD) equations and Navier - Stokes (NS) equations. The numerical results are compared with published experimental data. QGD and NS calculations produce close results that tightly fit the experimental data, especially for the monatomic argon and helium. The QGD algorithm is found to be more stable than the NS algorithm.

Simulation of the rarefied gas flow around a perpendicular disk

The present work contributes to define the domain of validity of two continuum approaches, based on Navier–Stokes (NS) and quasi gas-dynamic (QGD) equations, respectively. Results obtained using each method are compared with those obtained using a direct simulation Monte Carlo (DSMC) method considered as a reference. QGD equations differ from NS ones by the presence of additional dissipative terms. The present paper includes a brief presentation of QGD equations and DSMC procedures used here. The rarefied flow around a perpendicular disk has been considered for a freestream Mach number varying from 2 to 20, a Knudsen number equal to 0.1 and two levels of wall temperature.

A study of shock waves in expanding flows on the basis of spectroscopic experiments and quasi-gasdynamic equations

A comprehensive numerical and experimental study of normal shock waves in hypersonic axisymmetric jets of N is presented. The numerical interpretation is based on the quasi-gasdynamic (QGD) approach, and its generalization (QGDR) for the breakdown of rotational–translational equilibrium. The experimental part, based on diagnostics by high-sensitivity Raman spectroscopy, provides absolute density and rotational temperatures along the expansion axis, including the wake beyond the shock. These quantities are used as a reference for the numerical work. The limits of applicability of the QGD approach in terms of the local Knudsen number, the influence of the computational grid on the numerical solution, the breakdown of rotation–translation equilibrium, and the possible formation of a recirculation vortex immediately downstream from the normal shock wave are the main topics considered.

Experimental and numerical investigation of an axisymmetric supersonic jet

A comprehensive study of a steady axisymmetric supersonic jet of CO2, including experiment, theory, and numerical calculation, is presented. The experimental part, based on high-sensitivity Raman spectroscopy mapping, provides absolute density and rotational temperature maps covering the significant regions of the jet: the zone of silence, barrel shock, Mach disk, and subsonic region beyond the Mach disk. The interpretation is based on the quasi-gasdynamic (QGD) system of equations, and its generalization (QGDR) considering the translational–rotational breakdown of thermal equilibrium. QGD and QGDR systems of equations are solved numerically in terms of a finite-difference algorithm with the steady state attained as the limit of a time-evolving process. Numerical results show a good global agreement with experiment, and provide information on those quantities not measured in the experiment, like velocity field, Mach numbers, and pressures. According to the calculation the subsonic part of the jet, downstream of the Mach disk, encloses a low-velocity recirculation vortex ring.

Rarefied gas flow simulation based on quasigasdynamic equations

The treatment of rarefied gas flows by means of equations based on the mechanics of continuum media is desirable because solving such equations requires less computational resources than methods based on a molecular description. The present work aims at clarifying the domain of validity of two continuum approaches by comparing their results to a reference given by a direct simulation Monte Carlo method. The first continuum approach is based on the usual Navier-Stokes (NS) equations. The second one is based on the quasigasdynamic (QGD) equations that are derived from the Boltzmann equation. The present paper includes a self-consistent presentation of QGD equations. The flow along a flat plate has been considered for a freestream Mach number varying from 1.5 to 20 and a wall temperature taken successively equal to freestream and stagnation temperatures. The results suggest that the QGD equations are superior to the NS ones. A criterion is proposed for the validity of the continuum approaches.