CFD-CSD Analysis of Active Control of Helicopter Rotor for Performance Improvement

Three morphing rotor concepts, namely, trailing-edge-deflection (TED), leading-edge-deflection (LED), and active-twist, are investigated to improve rotor performance. This is a simulation-based investigation using both coupled computational fluid dynamics (CFD) – computational structural dynamics (CSD) and lifting-line-based comprehensive analysis. Coupled aero-structural simulations are performed to account for blade structural response due to aerodynamic loading generated by rotor morphing and pilot control to maintain the rotor trim state. A full-scale UH-60A Blackhawk rotor at two key flight conditions – high-speed forward flight and high-thrust forward-flight – is studied. Numerical experiments are conducted for several deployment strategies of the three morphing concepts. It is found that at high-speed forward-flight, trailing-edge-deflection and active-twist are more effective than leading-edge-deflection; the improvement in rotor lift-over-effective-drag (L/De) is about 6.9% and 4.9%, respectively. The improvement comes from the additional lift that is generated on the advancing side in the region of negative blade-tip loading without any drag increase. It results from an increase in the blade angle-of-attack (AOA) due to the pitch-up moments that are induced by the trailing-edge-deflection, and, in the case of active-twist they are directly applied to the blade. At a high-thrust condition, leading-edge-deflection performs better than the other two concepts – the improvement in L/De is about 18.2%. Retreating-side stall alleviation is the main cause for this improvement.