Automated aerodynamic optimization for lifting hypersonic vehicles at high altitude

Automated design optimization procedures are coupled to three-dimensional direct simulation Monte Carlo (DSMC) calculations for deformation of waverider-derived hypersonic vehicle shapes, in order to maximize the lift-to-drag ratio (L/D) under high altitude reentry conditions. For a lifting reentry vehicle, increased L/D under such conditions should permit a reduction in aerothermal heating, body forces and ionization effects, as well as an increase in range and other potential benefits related to mission cost and safety. In the optimization procedure employed in this paper, a new parallel Cartesian adaptive grid implementation of the DSMC method is integrated with surface deformation and threshold accepting algorithms for probabilistic multivariable optimization. Several waverider geometries, created through an inverse design technique, were used as starting points for optimization calculations, and multiple optimization runs were carried out for each starting shape. Including all iterations for each run, optimization calculations performed as part of this work involve 2880 independent three-dimensional DSMC simulations. A maximum increase in L/D of approximately 65% is demonstrated at Mach 14 and 90 km altitude, for a 5 m long vehicle with a global Knudsen number of 0.0033. Additional simulations were performed for this optimized geometry at design conditions, in order to assess the extent of continuum breakdown, flowfield characteristics, surface heat flux and temperatures, and the effect of leading edge bluntness on both heat flux and L/D values. To the authors' knowledge, this work represents the first integration of DSMC within an automated design optimization scheme, and demonstrates the potential efficacy of DSMC based aerodynamic optimization in reentry vehicle design. Copyright © 2012 American Institute of Aeronautics and Astronautics, Inc.