Adjoint optimization for optimal actuation on low Re airfoil

Flow control strategies have been shown to favorably modify aerodynamic performance at both high and low Reynolds number. We focus on an actuation strategy in which deformations are driven along the surface of the aerodynamic body. This strategy is promising because it leverages lightweight actuators that can operate across a wide range of timescales. We use two-dimensional high-fidelity simulations of a NACA0012 airfoil at a Reynolds number of 1000 to build on earlier work where the surface deformations were in the form of a travelling wave, parameterized by wavespeed and wavenumber. Here, we use adjoint-based optimization to identify the space- and time-varying deformation profile that maximizes mean lift and minimizes mean drag. We will compare the optimal deformation kinematics to the open-loop travelling wave actuation, and identify non-sinusoidal actuation characteristics that are beneficial to aerodynamic performance. Throughout, the optimal kinematics will be explained in terms of modifications induced in the vortex structures and pressure field near and in the wake of the airfoil.