AERODYNAMIC AND WAKE METHODOLOGY EVALUATION USING MODEL UH-60A EXPERIMENTAL-DATA

An evaluation of several aerodynamic methodologies; lifting line, lift ing surface and CFD, and wake methodologies; vortex lattice and consta nt vorticity contour models, is made to determine their applicability and validity in the prediction of helicopter airloads. Integrated blad e loads, blade pressures and blade strain data taken on a model UH-60A BLACK HAWK rotor are utilized to assess the capabilities of the aerod ynamic analyses. Prescribed torsional deformations, derived from test data, are used to create a uniform basis from which to compare the met hods. Test conditions chosen for this study include a high speed trans onic flow condition, a low speed, highly distorted wake condition, and a descending flight, blade-vortex interaction(BVI) condition. Results , in general, show good agreement between predicted and measured blade loads. Both 2-D and 3-D unsteady aerodynamic models show improvement over a quasi-steady model, with the 3-D Full Potential method (FPR) yi elding the best predictions in the blade tip region. Three wake models , UTRC's FREEWAKE, CDI's RotorCRAFT, and Johnson's dual-peak, modified Scully model perform comparably, all having difficulties in predictin g the complex vortex flow in the first quadrant. The FPR analysis yiel ds good predictions of chordwise pressure distributions. For the BVI c ondition, the inclusion of a discrete vortex segment within the comput ational domain of FPR yields a significantly improved BVI pulse predic tion. This translates to a largely improved BVI acoustic prediction.