A Discrete Sensitivity Solver for an Industrial CFD Code via Automatic Differentiation

Abstract

We report on development and validation of a discrete sensitivity solver for the BAE SYSTEMS/Airbus UK CFD code Flite3D. We used the Odyssée automatic differentiation (AD) tool to create a discrete forward sensitivity version of Flite3D Validation is via comparing sensitivities of integrated forces (lift, drag, side force) with respect to (w.r.t) angle-of-attack (AoA) α, calculated using the sensitivity solver and central-differencing. Validation, w.r.t. changes in the surface and field mesh, is performed by setting sensitivities of all mesh related quantities as if rotated by an infinitesimal angle Δα. Such sensitivities correspond to those calculated w.r.t AoA α. We investigate calculating discrete sensitivities under 2 approximations regarding so-called mesh sensitivities, concluding that they are not applicable to Flite3D. We present results of a wing geometry optimisation using forward sensitivities.