The Effect of a Preceding Blade on the Orthogonal Vortex Interaction

Experiments were performed where a blade of symmetrical profile was placed one chord upstream of another blade of identical dimensions but installed with miniature pressure transducers around the chord. The purpose of such a test was to simulate the effect of multiple orthogonal vortex interactions which may occur within the tail rotors of helicopters. It was found that when the upstream blade was installed, the pressure response experienced by the instrumented blade was similar in form but reduced in magnitude by 50% compared with results obtained without the upstream blade. This indicates that the vortex has the ability to reconnect and re-establish rotational and axial components after an initial cut. It also implies that noise and vibration radiating from tail rotors may be produced from multiple ‘cuts’ of the same vortex.