Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

High-fidelity simulations are performed to study active flow control techniques for alleviating deep dynamic stall of an SD7003 airfoil in plunging motion. The flow Reynolds number is Re=60000 and the freestream Mach number is M=0.1. Numerical simulations are performed with a finite-difference-based solver that incorporates high-order compact schemes for differentiation, interpolation, and filtering on a staggered grid. A mesh convergence study is conducted and results show good agreement with available data in terms of aerodynamic coefficients. Different spanwise arrangements of actuators are implemented to simulate blowing and suction at the airfoil leading edge. We observe that, for a specific frequency range of actuation, mean drag and drag fluctuations are substantially reduced while mean lift is maintained almost unaffected, especially for a two-dimensional (2D) actuator setup. For this frequency range, 2D flow actuation disrupts the formation of the dynamic stall vortex, which leads to drag reduction due to a pressure increase along the airfoil suction side, towards the trailing edge region. At the same time, pressure is reduced on the suction side near the leading edge, increasing lift and further reducing drag.