A Numerical Analysis of the Dynamic Stall Mechanisms on a Helicopter Rotor from Light to Deep Stall

Abstract

A loose coupling methodology between computational fluid dynamics and Comprehensive Analysis codes (elsA/HOST) is used to simulate a helicopter rotor in dynamic stall condition. Three stalled forward flight conditions have been selected in the wind tunnel 7A rotor test data to investigate the evolution of the stall mechanisms from a light stall to a deep stall condition. A decrease in the RPM is used to increase the rotor load. The lower the RPM the more severe the stall is. A double stall is observed in the lowest RPM case. The simulations are in satisfactory agreement with the experiment and are used to identify the mechanisms leading to the different stall events, notably the blade–vortex interaction. Rotormaps of the flow-separation regions are computed from numerical results, and similar regions of separated flow are observed in all the cases. These flow-separations originate from different aeroelastic mechanisms depending on their position on the rotor disk. As the rotor thrust coefficient is increased, some of these flow separations grow and lead to stall events.