Detached-Eddy Simulations for Active Flow Control

The present study conducted improved delayed detached-eddy simulations of actively controlled flows with a harmonic actuation on a backward-facing step and pulsed blowing on a pitching airfoil for reattachment and separation controls. Spectra analyses based on the unexcited flowfield data were carried out by using dynamic mode decomposition to identify spatial structures corresponding to the different Strouhal frequencies. The characteristic physical modes have been extracted for both cases. With better understanding of unsteady flow features, effective control practices were illustrated. For the backward-facing step case, the optimal excitation frequency was found to be 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 a 40% maximum reduction of the bubble length. For the airfoil case, with the optimum excitation frequency determined by the vortex-shedding mode of the baseline flow, a 194% increase of the lift-to-drag ratio was obtained; the pulsed blowing with the jet orifices in an antiphased manner was found to be very effective to damp the fluctuations of the lift around its mean value, though it led to a small decrease in mean lift.