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Development of unstable two-dimensional and three-dimensional disturbances of various modes in the boundary layer on the flat part of the model and their influence on the flow separation zone and the flow in the reattachment area on the compression ramp are studied with the direct numerical simulation. A supersonic flow with the flow Mach number M = 5.373 on a compression ramp with an angle of 5.5 degrees is simulated. The calculations are carried out using the CFD code HyCFS developed at the Laboratory of Computational Aerodynamics of the Institute of Theoretical and Applied Mechanics for solving the Navier–Stokes equations on hybrid-architecture computer clusters using graphical processing units. Based on the results of the numerical simulations data on the mean and nonstationary characteristics of the separated flow and surface characteristics in the vicinity of the boundary layer reattachment point have been obtained. The effect of developing large-scale turbulent structures in the transitional boundary layer on the fluctuations of the separation zone is studied, and the dynamics of critical parameters of the flow near the reattachment point is studied in detail. The calculation results show significant effect of the initial amplitudes of disturbances on the flow dynamics in the separation zone and the size of the zone. For sufficiently large amplitudes, laminar-turbulent transition occurs on the compression ramp. [ABSTRACT FROM AUTHOR]

Direct Numerical Simulation (DNS) is used to investigate linear and nonlinear stages of development of unstable disturbances and the transition to turbulence in a supersonic boundary layer on a flat plate with the Mach number of the external flow M = 6. The computations are carried out for the case of a cooled surface at a ratio of the plate temperature to the free-stream temperature Tw/T∞ = 1.4. According to linear stability theory calculations, the two-dimensional waves of the first mode in the boundary layer are completely stabilized at the considered flow parameters. The growth rates are maximum for unstable twodimensional disturbances of the second mode, while the three-dimensional waves of the second mode are also unstable. The results of DNS of linear and nonlinear stages of development of such disturbances are compared with the results of earlier computations of the laminar-turbulent transition on a flat plate with a temperature corresponding to the case of a thermally insulated surface, Tw/T∞ = 7. [ABSTRACT FROM AUTHOR]

The Kelvin–Helmholtz instability developing in the compressible mixing layer is simulated numerically using both the kinetic and continuum approaches. The computations are performed for a spatially periodic mixing layer at subsonic convective Mach numbers and low Reynolds numbers. The main part of the kinetic simulations are carried out with the Shakhov model kinetic equation but the simulations based on the Boltzmann equation are also conducted. A deterministic numerical method that directly solves the kinetic equations on a finite-difference grid in the multidimensional phase space is used. The computational code is adapted for implementation on hybrid computational clusters combining CPUs and GPUs. Navier–Stokes simulations of the Kelvin–Helmholtz instability are also performed and their results are compared with those of kinetic simulations. [ABSTRACT FROM AUTHOR]

A numerical study of the effects of disturbances on the interaction of a transitional supersonic flat-plate boundary layer with an incident oblique shock has been carried out. Direct numerical simulation of the transitional boundary layer on a flat plate is performed by solving the Navier–Stokes equations using two different CFD codes: parallel code CFS3D and hybrid parallel code HyCFS. The simulation is carried out in a three-dimensional computational domain at free-stream Mach number M = 1.45, which corresponds to the conditions of the experiments. At first stage, the transitional boundary layer is computed without an incident shock wave. Development of the disturbances introduced at the inflow boundary causes formation of a secondary flow in the form of three-dimensional longitudinal vortex structures that leads to the laminar-turbulent transition farther downstream. At the second stage, boundary conditions corresponding to the parameters behind an oblique shock are specified on a part of the upper boundary of the computational domain. As a result of the interaction of the boundary layer with an incident shock in the reflection region, a separation zone is formed. The presence of large-scale eddies developing in the boundary layer causes significant oscillations of the separation zone. Due to the shock wave boundary layer interaction the laminar-turbulent transition shifts upstream towards the separation region. [ABSTRACT FROM AUTHOR]

The direct simulation Monte Carlo method is used for numerical simulation at the molecular-kinetic level the development of the Kelvin–Helmholtz instability between two supersonic monatomic gas flows. To induce flow instability, no artificial disturbances are introduced and the waves of instability are developing from the statistical fluctuations inherent in the DSMC method. It is shown that modeling using the DSMC method makes it possible to fully reproduce the Kelvin–Helmholtz instability pattern observed in physical experiments and continuum simulations with the rapid growth of instability waves, the formation of vortex structures, vortex interaction and their sequential merging. [ABSTRACT FROM AUTHOR]

Modification of the serial Fortran code for solving unsteady 2D Euler equations for the mixture of compressible gas and polydisperse particles was carried out using OpenMP technology. Parallel code was used for the numerical simulation of shock wave propagation in 2D channel with obstacles filled with reactive Al-O2 gas particle mixture. Analysis was shown that obtained parallel speed-up is in a good agreement with the Amdahls law, which gives the estimate for serial code fraction about 30% [ABSTRACT FROM AUTHOR]

Unsteady interactions of shock waves are simulated numerically and analyzed taking into account viscosity and heat conductivity effects. Both a symmetric head-on collision of two shock waves of an equal strength and an asymmetric interaction of two shock waves propagating with different velocities are considered. In comparison with the classical inviscid case new effects connected with a finite width of the interacting shock waves have been observed. An increase in temperature and entropy is observed in the wake trailing behind a viscous spot formed by the intersecting symmetric finitewidth shock waves. An expanding viscous contact wave formed as a result of the asymmetric interaction generates weak pressure and disturbances in the space between two reflected shock waves. [ABSTRACT FROM AUTHOR]

In this work we present the preliminary results of numerical simulations of detonation wave propagation in a plane channel conducted with an in-home code solving the chemically reacting Euler equations on supercomputers with GPUs. The simulations are performed with four detailed chemical kinetics mechanisms (ONERA, Deiterding, modified Jachimowski, Peterson and Hanson models). The latter model includes a pressure-dependent reaction. The 1D and 2D Euler equations are solved for a hydrogen/ oxygen mixture using high-order shock-capturing TVD schemes and a finite-rate chemistry solver. The sizes of detonation cells obtained with different models are compared. [ABSTRACT FROM AUTHOR]

In the present work a computer code RCFS for numerical simulation of chemically reacting compressible flows on hybrid CPU/GPU supercomputers is developed. It solves 3D unsteady Euler equations for multispecies chemically reacting flows in general curvilinear coordinates using shock-capturing TVD schemes. Time advancement is carried out using the explicit Runge- Kutta TVD schemes. Program implementation uses CUDA application programming interface to perform GPU computations. Data between GPUs is distributed via domain decomposition technique. The developed code is verified on the number of test cases including supersonic flow over a cylinder. [ABSTRACT FROM AUTHOR]

There are various methods for calculating rarefied gas flows, in particular, statistical methods and deterministic methods based on the finite-difference solutions of the Boltzmann nonlinear kinetic equation and on the solutions of model kinetic equations. There is no universal method; each has its disadvantages in terms of efficiency or accuracy. The choice of the method depends on the problem to be solved and on parameters of calculated flows. Qualitative theoretical arguments help to determine the range of parameters of effectively solved problems for each method; however, it is advisable to perform comparative tests of calculations of the classical problems performed by different methods and with different parameters to have quantitative confirmation of this reasoning. The paper provides the results of the calculations performed by the authors with the help of the Direct Simulation Monte Carlo method and finite-difference methods of solving the Boltzmann equation and model kinetic equations. Based on this comparison, conclusions are made on selecting a particular method for flow simulations in various ranges of flow parameters. [ABSTRACT FROM AUTHOR]

The paper presents the software implementation of the Boltzmann equation solver based on the deterministic finitedifference method. The solver allows one to carry out parallel computations of rarefied flows on a hybrid computational cluster with arbitrary number of central processor units (CPU) and graphical processor units (GPU). Employment of GPUs leads to a significant acceleration of the computations, which enables us to simulate two-dimensional flows with high resolution in a reasonable time. The developed numerical code was validated by comparing the obtained solutions with the Direct Simulation Monte Carlo (DSMC) data. For this purpose the supersonic flow past a flat plate at zero angle of attack is used as a test case. [ABSTRACT FROM AUTHOR]