HSCT configuration design using response surface approximations of supersonic Euler aerodynamics

A method has been developed to efficiently implement supersonic aerodynamic predictions from Euler solutions into a highly constrained, multidisciplinary design optimization of a High-Speed Civil Transport (HSCT) configuration. The method alleviates the large computational burden associated with performing CFD analyses and eliminates the numerical noise present in the analyses through the use of response surface (RS) methodologies, a variation of the variable-complexity modeling (VCM) technique, and coarse grained parallel computing. Variablecomplexity modeling techniques allow one to take advantage of information gained from inexpensive lower fidelity models while maintaining the accuracy of the more expensive high fidelity methods. In this research, simple conceptual level aerodynamic models provide the functional form of the drag polar. Response surface models are therefore created for the intervening functions (drag polar shape parameters) revealed by the simple models instead of for the drag itself. Optimization results using linear theory RS models are used to select the allowable ranges of the design variables. Stepwise regression analysis, performed using data from linear theory aerodynamic results, provides information on the relative importance of each term in the polynomial RS models. With this information, reduced term RS models representing a correction to the linear theory RS model predictions are constructed using fewer Euler evaluations. Studies into five, ten, fifteen, and ∗Graduate Research Assistant, Dept. of Aerospace and Ocean Engineering. Current Position: Postdoctoral Research Associate, Dept. of Aeronautics and Astronautics, University of Washington, Seattle, WA, Member AIAA. †Postdoctoral Research Associate, National Research Council/NASA Langley Research Center, Hampton, VA, Member AIAA. ‡Graduate Research Assistant, Dept. of Aerospace and Ocean Engineering, Student Member AIAA. §Professor and Dept. Head of Aerospace and Ocean Engineering, Associate Fellow AIAA. ¶Professor of Aerospace and Ocean Engineering, Associate Fellow AIAA. ‖Professor of Aerospace Engineering, Mechanics and Engineering Science, University of Florida, Gainesville, FL, Fellow AIAA ∗∗Professor of Computer Science and Mathematics twenty variable HSCT design problems show that accurate results can be obtained with the reduced term models at a fraction of the cost of creating the full term quadratic RS models. Specifically, 11 hour, 47 hour, 115 hour, and 255 hour savings in CPU time on a single 75 MHz IP21 processor of a SGI Power Challenge are obtained for the five, ten, fifteen, and twenty variable design problems, respectively. Errors in the RS model cruise drag predictions, based on actual Euler calculations, for the optimal designs range from 0.1 counts to 0.8 counts for the twenty variable optimum.