Combustion-Powered Actuation for Dynamic Stall Suppression - Simulations and Low-Mach Experiments

An investigation on dynamic-stall suppression capabilities of combustion-powered actuation (COMPACT) applied to a tabbed VR-12 airfoil is presented. In the first section, results from computational fluid dynamics (CFD) simulations carried out at Mach numbers from 0.3 to 0.5 are presented. Several geometric parameters are varied including the slot chordwise location and angle. Actuation pulse amplitude, frequency, and timing are also varied. The simulations suggest that cycle-averaged lift increases of approximately 4% and 8% with respect to the baseline airfoil are possible at Mach numbers of 0.4 and 0.3 for deep and near-deep dynamic-stall conditions. In the second section, static-stall results from low-speed wind-tunnel experiments are presented. Low-speed experiments and high-speed CFD suggest that slots oriented tangential to the airfoil surface produce stronger benefits than slots oriented normal to the chordline. Low-speed experiments confirm that chordwise slot locations suitable for Mach 0.3-0.4 stall suppression (based on CFD) will also be effective at lower Mach numbers. INTRODUCTION Problems associated with dynamic stall continue to limit rotorcraft speed and efficiency. Retreating-blade stall (RBS) typically occurs between the blade mid-span and tip near the ψ = 270° position. Although it commonly occurs on rotorcraft operating near the edge of their flight envelope, performance at these conditions plays an important role in rotor design as demand increases for faster and more agile rotorcraft with higher lift capacity. Furthermore, rotor blades are designed so that the extreme conditions at which stall occurs size key parameters such as blade chord. The adverse effects of RBS can be mitigated through alleviation of dynamic stall at Mach numbers from 0.2 to 0.5. Previous work involving mechanical leading-edge slats, synthetic jets, and plasma actuation have shown some success, but each technique has its weaknesses or challenges (Refs. 1-4). Slats are very effective aerodynamically, however, overcoming advancing-side drag penalty has proven to be extremely difficult in terms of mechanical design. Synthetic jets and plasma actuation have shown significant promise across a range of speeds. Plasma actuation is the subject of several current research efforts, two of which are described in Refs. 5 and 6. Combustion-powered actuation (COMPACT) provides a potential means for mitigating dynamic stall across a broad range of Mach numbers. COMPACT actuation can provide