Adjoint-based Noise minimization via Porous Material

We present a discrete adjoint-based optimization framework to obtain the optimal distribution of the porous material over the trailing edge of a 3-D flat plate. The near-body strength of the noise source generated by the unsteady turbulent flow field is computed using a high-fidelity large-eddy simulation (LES). The acoustic signal thus generated is then propagated to the far-field using the acoustic perturbation equations(APE). The design gradients are computed using the forward and reverse modes of algorithmic differentiation (AD). The increase of memory requirement in the reverse mode AD is alleviated by checkpointing. By optimally controlling the material porosity and permeability, it is possible to minimize the turbulence intensity responsible for noise generation at the trailing edge and thus significantly reduce the radiated noise. Theoptimal porous trailing-edge design achieves a noise reduction of up to 18dB.