Investigation of the unsteady reverse flow airloads at high advance ratios

Abstract

The comprehensive analysis UMARC has been modified to include a model for dynamic stall in the reverse flow region for high advance ratio helicopter. The reverse flow stall model adapts the Leishman-Beddoes dynamic stall model with concepts from a flat plate in accelerating flow. The model is evaluated against airloads data from the reverse flow region of the UH-60A slowed rotor test at high advance ratios between ? = 0.4–1.0. The dynamic stall model predicts dynamic stall in the reverse flow for all the test cases, but does not have a significant impact on the advancing side of the rotor. At lower advance ratios (? = 0.4 and 0.6), the azimuth of dynamic stall is well predicted and the correlation with the measured airloads in the reverse flow is improved. At ? = 1.0, the model predicts multiple vortex shedding, which are present in the test, but the phase agreement is not satisfactory.