Computational Investigation and Fundamental Understanding of a Slowed UH-60A Rotor at High Advance Ratios

The work carries out coupled Computational Fluid Dynamics and Comprehensive Analysis (Helios/RCAS) of a fullscale UH-60A rotor slowed down to 40% of nominal RPM, operating at advance ratios up to 1.0. The objectives of the work are to 1) validate the analysis with detailed aerodynamic measurements under loading conditions unique to this regime, and 2) to use the analysis to complement test measurements and expand fundamental understanding of slowed rotor and high advance ratio physics. Airloads validation shows excellent agreement with normal force, but pitching moments are poorly predicted on both the advancing (negative lifting) and retreating (reversed flow) blades. Fundamental understanding is gained of the physics of the reversed flow region, wake interactions, advancing and retreating blade moment impulses, differential span loading, and blade deformations - as influenced by RPM and advance ratio. Flow field visualizations show in exceptional detail the unconventional wake patterns, the reversed flow dynamic stall vortex progression, blade-on-blade interactions, reversed-flow-edge vortex, and root vortices. Comparisons of rotor performance and trim controls are documented, showing reasonable trend agreement.