Aerodynamic Database Generation for a Complex Hypersonic Vehicle Configuration Utilizing Variable-Fidelity Kriging

This work seeks to provide a proof-of-concept for the use of variable-fidelity (VF) kriging to approximate the lift and drag values for a complex hypersonic flight vehicle. Otherwise known as aerodynamic database generation within the aerospace engineering community, the force or moment experienced by a vehicle due to airflow, as a function of independent inputs such as flight speed or attitude, is approximated via some mathematical form. In the case of this work, VF kriging is implemented such that the vehicle response is interpolated directly through the points of high-fidelity (HF) simulation data while the trends of the response approximation are guided by low-fidelity (LF) information. High-fidelity simulations are implemented via the Euler flow computational software package Cart3D. The low-fidelity information is given by supersonic-hypersonic small-disturbance theory implemented in a surface pressure estimation code, developed specifically for this work for completely arbitrary body shapes represented by unstructured, triangular-cell surface meshes. The major contribution is a framework that connects the two fidelity levels to VF kriging routines to produce lift and drag approximations of arbitrary complex vehicles under hypersonic flight conditions. Assessment of the quality of the approximations is given by the root-mean-square error (RMSE) between the VF kriging surrogates and high-fidelity simulations performed over the same independent input domain. Results in two dimensions show that the use of VF kriging, to produce an interpolant as a function of angle-of-attack and Mach number, increases surrogate accuracy by nearly an order of magnitude for lift and by over twenty times for drag, when compared to ordinary kriging without variable-fidelity modeling. Three-dimensional surrogates, with input of angle-of-attack and two independent elevon control surface deflections, show roughly two and four times more accuracy for lift and drag, respectively, compared to ordinary kriging. Such significant increases in accuracy show promise for the use of VF kriging in accelerated and tractable hypersonic vehicle design trades while simultaneously injecting high-fidelity information into vehicle synthesis far earlier in the design cycle