High-Altitude Capsule Aerodynamics with Real Gas Effects

Re-entry capsule aerodynamics within a wide range of angles of attack and flight altitudes are examined by the direct simulation Monte Carlo method. The local bridging method is verified by comparison with results of simulations. Capsule stability is analyzed for flight altitudes from 130 km down to 85 km. Comparison between computed and free flight data shows a good agreement. A qualitative change of heat transfer coefficient behavior for different angles of attack during the descent is revealed. The influence of chemical reactions on aerodynamics and flowfields at 85 km is shown to be significant. For a flow simulation in the near-continuum regime, a parallel version of the direct simulation code, with static and dynamic load balancing techniques, is used. An efficiency of about 80% is obtained for 256 processors using dynamic load balancing. Nomenclature CA = axial force normalized by p^U^S/2 CH - heat transfer normalized by p^U^S/ Cm - pitching moment normalized by p^ CN = normal force coefficient normalized by p^U^S/2 Ck = local coefficient Q cont = continuum coefficient ckjm = free molecular coefficient Fb = bridging function H = altitude, km Kn = Knudsen number KnotOC = Knudsen number based on /z (), TO, and p^ L = characteristic length, m NI = number of molecules in cell / Nm = average number of simulated molecules in the computational domain Wproc = number of processors S = characteristic size, m2 TO = stagnation temperature, K kaic = calculation time rcom = communication time Adic = synchronizatio n time fun = total operation time f/oo = freestream velocity, m/s a = angle of attack, deg £/ = volume of interaction region in cell /, m3 jjio = stagnation viscosity, kg/m-s v"1 = majorant frequency, s"1 Poo = freestream density, kg/m3