Aerodynamic and Wake Methodology Evaluation Using Model UH-60A Experimental Data

An evaluation of several aerodynamic methodologies; lifting line, lifting surface and CFD, and wake methodologies; vortex lattice and constant vorticity contour models, is made to determine their applicability and validity in the prediction of helicopter airloads. Integrated blade loads, blade pressures and blade strain data taken on a model UH-60A BLACK HAWK rotor are utilized to assess the capabilities of the aerodynamic analyses. Prescribed torsional deformations, derived from test data, are used to create a uniform basis from which to compare the methods. Test conditions chosen for this study include a high speed transonic flow condition, a low speed highly distorted wake condition, and a 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 CFD method yielding the best predictions in the blade tip region. Three wake models, UTRC's FREEWARE, CDI's rotorCRAFT, and a Johnson dual-peak model perform comparably, all having difficulties in predicting the complex vortex flow in the first quadrant. The FPR analysis yields good predictions of chordwise pressure distributions. For the BVI condition, the inclusion of a discrete vortex segment within the computational domain of FPR yields a significantly improved BVI pulse prediction. This translates to a largely improved BVI acoustic prediction.