An Unsteady Aerodynamic/Aeroacoustic Optimization Framework Using Continuous Adjoint

In this paper, an unsteady aerodynamic/aeroacoustic optimization framework is presented. This is based on the continuous adjointmethod to a hybrid acoustic prediction tool, in which the near-field flow solution results from an unsteady CFD simulation while the acoustic propagation to far-field makes use of an acoustic analogy. The CFD simulation is performed using the in-house GPU-enabled URANS equations’ solver for which a continuous adjoint solver is available. The noise prediction tool and its adjoint are developed based on the permeable version of the Ffowcs Williams and Hawkings (FW-H) analogy, solved in the frequency domain. Its implementation is verified w.r.t. the analytical solution of the sound field from a monopole source in uniform flow. Then, the accuracy of the hybrid solver is verified by comparing the sound directivity computed by the FW-H analogy with that of a CFD run, for a 2D pitching airfoil in a subsonic inviscid flow. The accuracy of the sensitivities computed using the unsteady adjoint solver is verified w.r.t. those computed by finite differences. Finally, the programmed software is used to optimize the shape of the pitching airfoil, aiming at min. noise with an equality constraint for the lift.

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