Multi-Fidelity Design Optimization of Low-Boom Supersonic Business Jets

The practical use of high-fidelity multidisciplinary optimization techniques in low-boom supersonic business jet designs has been limited because of the high computational cost associated with CFD-based evaluations of both the performance and the loudness of the ground boom of the aircraft. This is particularly true of designs that involve the sonic boom loudness as either a cost function or a constraint because gradient-free optimization techniques may become necessary, leading to even larger numbers of function evaluations. If, in addition, the objective of the design method is to account for the performance of the aircraft throughout its mission (T/O and landing, climb, acceleration , etc.) while including important multidisciplinary trade-offs between the relevant disciplines (performance, boom, structures, stability and control, propulsion, etc.) the situation only worsens. In order to overcome these limitations, we propose a hierarchical multi-fidelity design approach where high-fidelity models are only used where and when they are needed to correct the shortcomings of the low-fidelity models. Our design approach consists of two basic components: a multidisciplinary aircraft synthesis tool (PASS) that uses highly-tuned low-fidelity models of all of the relevant disciplines and computes the complete mission profile of the aircraft, and a hierarchical, multi-fidelity environment for the creation of response surfaces for aerodynamic performance and sonic boom loudness (BOOM-UA) that attempts to achieve the accuracy of an Euler-based design strategy. This procedure is used to create three design alternatives for a Mach 1.6, 6-8 passenger supersonic business jet configuration with a range of 4,500 nmi and with a T/O field length that is shorter than 6,000 ft. Optimized results are obtained with much lower computational cost than the direct, high-fidelity design alternative. The validation of these design results using the high-fidelity model show very good agreement for the aircraft performance and highlights the need for improved response surface fitting techniques for the boom loudness approximations.