Numerical Modeling of High Altitude Aerodynamics of Reentry Vehicles

Abstract

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.