Alexander V. Kashkovsky

Aerodynamics of space station “Mir” during aeroassisted controlled descent

Future descent of space station “Mir” requires the choice of an optimal configuration (positions of solar arrays) which allows one to minimize the disturbing aerodynamic torques and maximize the drag. The aerodynamic characteristics of two configurations with required positions of solar arrays are studied by engineering and statistical methods along the descent trajectory. The study showed that a decrease in the flight altitude from 200 to 130 km does not exert a noticeable effect on the magnitude of the force and moment coefficients and also revealed the reasons decreasing the accuracy of the engineering prediction.

DSMC Modeling of High-Temperature Chemical Reactions in Air

A novel approach to modeling high-temperature nonequilibrium dissociation in air with the DSMC method is proposed. Microscopic information on vibrationally specific reaction cross sections, which is necessary for such modeling, is determined numerically from known macroscopic information on the dependence of the reaction rate constant on translational and vibrational temperatures. DSMC computations with the use of the calculated nitrogen and oxygen dissociation cross sections show that the proposed model yields a correct reaction rate in vibrational-translational nonequilibrium. The use of the new model in DSMC computations of high-altitude aerothermodynamics results in obtaining a noticeably different flow structure and a higher heat flux as compared with that predicted by standard DSMC models.

Aspects of GPU perfomance in algorithms with random memory access

The numerical code for solving the Boltzmann equation on the hybrid computational cluster using the Direct Simulation Monte Carlo (DSMC) method showed that on Tesla K40 accelerators computational performance drops dramatically with increase of percentage of occupied GPU memory. Testing revealed that memory access time increases tens of times after certain critical percentage of memory is occupied. Moreover, it seems to be the common problem of all NVidia’s GPUs arising from its architecture. Few modifications of the numerical algorithm were suggested to overcome this problem. One of them, based on the splitting the memory into “virtual” blocks, resulted in 2.5 times speed up.The numerical code for solving the Boltzmann equation on the hybrid computational cluster using the Direct Simulation Monte Carlo (DSMC) method showed that on Tesla K40 accelerators computational performance drops dramatically with increase of percentage of occupied GPU memory. Testing revealed that memory access time increases tens of times after certain critical percentage of memory is occupied. Moreover, it seems to be the common problem of all NVidia’s GPUs arising from its architecture. Few modifications of the numerical algorithm were suggested to overcome this problem. One of them, based on the splitting the memory into “virtual” blocks, resulted in 2.5 times speed up.

A numerical code for the simulation of non-equilibrium chemically reacting flows on hybrid CPU-GPU clusters

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.

Numerical Modeling of High Altitude Aerodynamics of Reentry Vehicles

The use of two modications of the local bridging method for approximate estimates of aerodynamic characteristics of complex-shaped reentry vehicles in a wide range of Knudsen numbers is presented. Additional computations by the DSMC method are used to estimate the accuracy of these engineering methods. he orbit of advanced space vehicles lies at altitudes of about 300-400 km. During their reentry to the Earth, the vehicles rst experience the action of the free-molecular o w, then enter the transitional regime, and nally , beginning from an altitude of 80 km, descend in the continuum o w. For successful reentry of the vehicle to the Earth, it is necessary to know the behavior of its aerodynamic characteristics in all o w regimes. Computation of aerodynamic characteristics of reentry vehicles in the free-molecular o w does not involve many diculties because theoretical approaches have been developed for simple shapes and the Test Particle Monte Carlo method can be readily used for more complicated shapes. Methods for computing aerodynamic characteristics in the continuum o w have also been adequately developed. The study of aerodynamic characteristics in the transitional o w regime (0:001 < Kn < 10) is a rather complicated problem. The Navier-Stokes equations fairly suitable in the continuum medium, yield, strictly speaking, incorrect results in the transitional regime and require special modications for taking into account o w slipping. The Direct Statistical Monte Carlo (DSMC) method provides rather accurate values of aerodynamic characteristics with allowance for physical and chemical processes but requires large amounts of computer memory and performance, which hinders the use of this method. There are several software systems that allow simulation of 3D-aerodynamics of reentry vehicles in the transitional regime (e.g., SMILE, DAC), but their application at the initial stage of spacecraft design and trajectory analysis is unreasonably expensive because it is necessary to compute a large number of variants for dieren t angles of attack and sideslip and for dieren t o w parameters. The approach for solving this problem is to use approximate engineering methods, which oer acceptable accuracy with a short computation time. For instance, the existing aerodynamic software system Ramses 1 includes an engineering method based on local bridging interpolation between the free-molecular and continuum o w regimes to obtain of local aerodynamic characteristics in the transitional regime. Accuracy evaluation of engineering methods is dicult because of the lack of experimental data on aerodynamic characteristics of modern spacecraft in the transitional regime. One possible way is a comparison with the complicated but accurate DSMC method. The aerodynamic characteristics of promising reentry capsules KHEOPS and Clipper in free-molecular and transitional regimes were examined in the present paper.