An Adjoint-based Aerodynamic Shape Optimization Strategy for Trimmed Aircraft with Active Engines

Abstract

An adjoint-based Trim-Corrected Optimization Strategy (TCOS) with active engines is presented with applications to a three-dimensional modern transport aircraft configuration. The airframe drag is minimized using a gradient-based optimization algorithm by adapting the shape parameters alone while a trim process guarantees by means of the trim parameters that the design satisfies the aircrafts steady-state equilibrium of forces and moments. Following this approach, the sensitivity of the objective function is corrected in order to be consistent with the trim constraints. The backbone of the design evaluation process is the HPC-based environment FlowSimulator allowing for an in-memory data exchange between the involved primal tools and their dual counterparts. These are a freeform deformation parametrization, a mesh deformation method based on the linear elasticity analogy preserving the fuselage shape during the horizontal tail plane deflection and the finite-volume RANS solver TAU including the numerical engine treatment and a fully differentiated discrete-adjoint implementation. Several optimization studies were performed to quantify the impact of an active and controlled engine on the optimization result, but also to compare the TCOS performance against that of a conventional gradient-based Direct Optimization Strategy (DOS) in which the trim constraints and parameters are explicitly handled by the optimization algorithm. TCOS was found to achieve similar overall drag reductions as DOS. However, TCOS was able to significantly reduce the drag during the first few iterations while resulting in a feasible design in every optimization iteration.