Aerodynamic shape optimization of a subsonic inlet using three-dimensional Euler computation

A design optimization study of a subsonic inlet is presented where the peak Mach number at cruise condition on the inside of the inlet surface is the objective function to be minimized and inlet lip shape parameters are the design variables, The peak Mach number at takeoff, rolling takeoff, static, and crosswind conditions are constrained to an upper limit, The three-dimensional flowfield is predicted by the NPARC computational fluid dynamics code in Euler mode, A GRAPE-(grids about airfoils using Poisson's equation) based three-dimensional grid generator is employed to generate a C-grid around the inlet. Constrained numerical optimization is carried out by interfacing NPARC with the automated design synthesis optimization code, The constrained optimum is obtained by the method of feasible directions, The required gradients for optimization are computed via forward difference scheme. At the baseline (initial) design, takeoff, rolling takeoff, and crosswind conditions have their peak Mach numbers exceeding the upper bounds. However, at the constrained optimum design, only the upper limit on the takeoff peak Mach number is found to be critical with no appreciable change in cruise Mach number.