Controlling Flow Separation on a Thick Airfoil Using Backward Traveling Waves
Amir Akbarzadeh, Iman Borazjani
Abstract
Large-eddy simulations (LESs) of low-Reynolds-number flow over a NACA0018 airfoil are performed to investigate flow control at the stall angle of attack (15 deg) by low-amplitude surface waves (actuations) of different types (backward/forward traveling and standing waves) on the airfoil’s suction side. It is found that the backward (toward downstream) traveling waves, inspired from aquatic swimmers, are more effective than forward traveling and standing wave actuations. The results of simulations show that a backward traveling wave with a reduced frequency (, where is frequency; , chord length; and , free flow velocity), a nondimensional wavelength (, where is dimensional wavelength), and a nondimensional amplitude (, where is dimensional amplitude) can suppress stall. In contrast, the flow over the airfoil with either standing or forward traveling wave actuations separates from the leading edge similar to the baseline. Consequently, the backward traveling wave creates the highest lift-to-drag ratio. For traveling waves at a higher amplitude , however, the shear layer becomes unstable from the actuation point and creates periodic coherent structures. Therefore, the lift coefficient decreases compared with the low-amplitude case.