An investigation into predicting vortex ring state in rotary aircraft

Results from wind tunnel experiments and Computational Fluid Dynamic (CFD) simulations have been presented which suggest it may be possible to predict when a rotary aircraft will enter Vortex Ring State (VRS). Results suggest that the formation of a small, toroidal vortex which develops approximately 2.5 blade radiuses above the rotor plane of a model helicopter develops over time as the model helicopter descends into VRS. As the toroidal vortex develops, the lift the rotor is producing decreases over time until the toroidal vortex has reached the rotor plane of the model helicopter. Repeating the experiment using the same model at different wind tunnel and rotor speeds to cause it to descend into VRS produces the same results. Repeating the experiment using a propeller also produces the same results. CFD simulations show the formation of the toroidal vortex and development into VRS.

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