The Effect of Micro-Cavity Actuator Geometry on Dynamic Stall Control Authority

The effectiveness of a micro-cavity resonator is experimentally investigated on a dynamically pitching NACA 0012 airfoil as a means of dynamic stall control. The micro-cavity is positioned and dimensioned to excite self-induced resonant oscillations during the deep stall period to prevent laminar separation bubble bursting. Two physical airfoils were manufactured (aluminum and 3D printed resin), both with a micro-cavity. Wind tunnel testing at M = 0.20 – 0.25, k = 0.039 – 0.049 and Re = 6.8 – 8.35 ×〖10〗^5 revealed that the resin (plastic) micro-cavity airfoil significantly improved aerodynamic performance. Lift hysteresis was reduced by up to 68.3% and positive aerodynamic damping was generated. By comparison, the micro-cavity on the aluminum airfoil delivered only 41 - 56% lift hysteresis reduction with intermittent effective control. To investigate this discrepancy, cavity chordwise position, corner sharpness, L/D ratio, and Mach number effects were considered. Scans of each cavity revealed a significant difference in L/D, which resulted in different predicted resonant tones. Previous studies of cavity L/D’s effect on pressure fluctuations show that deeper cavities exhibit a strong periodic component, whereas shallow cavities are more random in character. Thus, the current work suggests that stronger periodicity may be more important in LSB stabilization than targeting specific resonant tones centered about the exact LSB receptivity range.