Multi-Objective Shape Optimization Study for a Subsonic Submerged Inlet

Abstract

The findings of a multi-objective shape optimization study conducted for a subsonic submerged air vehicle inlet are summarized. The objective functions of the optimization problem are distortion and swirl indices defined by the distribution of flow parameters over the exit cross section of the inlet. The geometry alteration is performed by placing a protrusion in the shape of a fin on the baseline inlet surface. Therefore, the design variables of the optimization problem are chosen to be the geometrical parameters defining the fin protrusion, namely, fin height, length, and incidence angle. The trade-off (also known as the e-constraint) method is employed for finding the Pareto optimal set formed by the nondominated solutions of the feasible design space. Because the flow-domain solution is required for every step along the line search, an automated optimization loop is constructed by integrating the optimizer with a surface modeler, a mesh generator, and a flow solver through which the flow parameters over the compressor face are computed. In addition, the trade study for fin protrusion, and the analyses and the comparison of the baseline and Pareto optimal solutions are presented, and observations concerning grid resolution and convergence behavior are discussed. Nomenclature DC(φ) = distortion index f (x) = objective function g(x) = constraint function hfin = height of the fin protrusion, m lfin = length of the fin protrusion, m