Improved delayed detached-eddy simulations of actively controlled flow

Abstract

In this study, Improved Delayed Detached-Eddy Simulations (IDDES) were conducted for active flow control with a harmonic actuation on a backward-facing step (BFS) and pulsed blowing on a NACA0015 airfoil for reattachment and separation controls. By using Dynamic Mode Decomposition, the characteristic physical modes of the unexcited flow have been extracted for both cases. With better understanding of unsteady flow features, effective control practices were illustrated. For the BFS case, the optimum excitation frequency was found identical with the step-mode frequency of the baseline flow. Such harmonic actuation enhanced the pairing process, forming the largest scale spanwise coherent structures in the free shear layer, resulting in 40% the maximum reduction of the bubble length. For the airfoil case, with the optimum excitation frequency that determined by the vortex-shedding mode of the baseline flow, 194% the increase of the lift-to-drag ratio was obtained.