Upstream Active Gurney Flap for Rotorcraft Vibration Reduction

This paper examines the effectiveness of active Gurney flaps, extending from 70-80% span, in reducing the 4/rev vibratory hub loads of a UH-60A Blackhawk helicopter at 0.35 advance ratio. The Gurney flaps are located at 90% chord on the lower surface of the blade, and are nominally deployed to an amplitude of 0.5% chord. A rotor comprehensive analysis is used for the simulations in this pa- per with Navier-Stokes CFD based computations used to generate the increments in blade sectional aerodynamic coefficients due to Gurney flap deployment. The study examines hub vibratory loads for open loop parametric phase sweeps at Gurney flap actuation frequencies of 3, 4, and 5/rev, followed by vibratory load reductions with the use of T-matrix multi-cyclic controllers. For the flight condition considered, results showed that Gurney flap actuation was most influential in reducing the vertical vibratory hub force. 4/rev actuation input was most effective, producing 80% reduction, while 5/rev actuation produced about 60% reduction, both with actuation amplitude of 0.5% chord. A multi-cyclic controller using 3 and 4/rev Gurney flap actuation reduced the in-plane and vertical vibratory hub forces by 52% and the in-plane vibratory hub moments by 46%. When 3, 4, and 5/rev actuation fre- quencies were used, reductions in vertical and in-plane vibratory hub forces increased to 63% while 48% reductions in in-plane moments were observed.