Post-stall flow control using a sawtooth plasma actuator in burst mode

Experimentally investigation is conducted on the control of post-stall airfoil aerodynamics using a vortex generator type plasma actuator (VG-PA), in burst mode (BM) at a Reynolds number Re of 0.77 x 10(5). The VG-PA has two sawtooth-shaped electrodes that are separated by a dielectric layer and are arranged with opposite saw-teeth pointing at each other, resulting in a spanwise periodic change in electrode gap. The dependence of the lift coefficient C-L of a NACA 0015 airfoil on the non-dimensional burst frequency F+ (= f(b)c/U infinity, where c and U infinity are the airfoil chord length and the freestream velocity, respectively) and duty cycle (DC) is investigated systematically; 144 combinations of F+ (= 0.3-9.0) and DC (= 1%-100%) are examined. Under steady actuation (DC = 100%), the stall angle-of-attack alpha is postponed from 13 degrees to 18 degrees and the maximum C-L exceeds that of no control by 9%. Given the same applied voltage V-a, this alpha is postponed to 16 degrees under the optimum BM parameters (F+ = 0.6, DC = 5%), but its maximum C-L exceeds that of no control by 27.5%. Furthermore, its consumption of power is only 5% of that under the steady actuation. Careful examination of the flow structure generated by the VG-PA as well as the perturbed airfoil wake unveils distinct mechanisms behind the lift enhancement under the steady and BM actuations. While the former depends on the direct injection of large momentum and vorticity, the latter is linked to the spanwise vortices periodically-induced by the VG-PA. (c) 2020 Elsevier Masson SAS. All rights reserved.