A Numerical Investigation of the Influence of the Blade–Vortex Interaction on the Dynamic Stall Onset

Abstract

Recently, fluid–structure coupling simulations of helicopter rotors in high-thrust forward flight suggested that dynamic stall might be triggered by the blade–vortex interaction. However, no clear evidence of a correlation between dynamic stall and blade–vortex interaction has yet been given. We propose in this paper a simplified two-dimensional numerical model that can be used to indicate the role that the blade–vortex interaction plays in dynamic stall onset for different flight conditions. In this model, the rotor blade element is considered in pitching oscillation motion with a nonuniform translation, and a simplified vortex model can be introduced or not in the simulation to highlight the effect of blade–vortex interaction. All flow parameters of this simplified model are deduced from data provided by previous three-dimensional high-fidelity fluid–structure simulations. The method is used for validation and analysis of three flight conditions. The results show that, for the two cases with moderate advance ratio, the dynamic stall event is only triggered when a blade–vortex interaction occurs in the stall region. For the high-speed test case, the dynamic stall event seems to be only triggered by the very high angle of attack due to the motion of the blade.

Simultaneous Pressure and Displacement Measurement on Helicopter Rotor Blades Using a Binocular Stereophotogrammetry PSP System

“…At the backward blade, the forward flight speed is contrary to the rotating speed of the blade, which makes the inner side of the backward blade in the reflux zone. Moreover, in order to overcome the unbalanced lift caused by the uneven distribution of airflow velocity, the trailing blades are in a state of high attack angle, and there is a possibility of dynamic stall [4,5]. When the helicopter flies forward at a low speed, the sudden drop of the tip pressure will cause the blade to have a strong tip vortex overflow, which seriously affects the subsequent blades and brings about a significant problem of blade vortex interference [6][7][8].…”