Multifidelity Design Optimization of Low-Boom Supersonic 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 computational fluid dynamics-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 techniquesmaybecomenecessary, leading to even largernumbers of function evaluations. If, in addition, the objective of the design method is to account for the performance of the aircraft throughout its full-flight mission while including important multidisciplinary tradeoffs between the relevant disciplines the situation only complicates. To overcome these limitations,we propose a hierarchicalmultifidelity design approachwhere high-fidelitymodels are only usedwhere andwhen theyareneeded to correct the shortcomingsof the low-fidelitymodels.Ourdesignapproach consists of two basic components: amultidisciplinary 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, multifidelity environment for the creation of response surfaces for aerodynamic performance and sonic boom loudness (BOOM-UA) that attempts to achieve the accuracy of anEuler-based design strategy. This procedure is used to create three design alternatives for aMach 1.6, 6–8 passenger supersonic business-jet configurationwith a range of 4500 nmile andwith a takeofffield length that is shorter than 6000 ft.Optimized results are obtainedwithmuch lower computational cost than the direct, high-fidelity design alternative. The validation of these design results using the high-fidelity model shows very good agreement for the aircraft performance and highlights the need for improved response surface fitting techniques for the boom loudness approximations.