Blade-vortex interaction

Literature distinguishes different classes of BVIs in helicopter rotors depending on the impacting vortex axis with respect to the blade span.

In order to understand the BVI flow characteristic more closely and suppress the noise and vibration actively, it is important to predict the BVIs precisely.

In 1994, researchers from German DLR, French ONERA, NASA Langley, and the US Army Aeroflightdynamics Directorate (AFDD) formed an international consortium to carry out a comprehensive experimental program which is denominated HART I (Higher Harmonic Control Aeroacoustic Rotor Test I) project at the large low speed facility of DNW (German-Dutch wind tunnel).

In this test, a 40% scaled BO-105 rotor model along with a fuselage is used, a range of sophisticated measurement techniques are introduced to measure the noise level, blade surface pressure, tip vortices, blade motions, and structural moments with and without the application of HHC (Higher Harmonic Control) pitch control inputs.

Currently，the analytical methods for BVI phenomenon capturing are mainly based on the free wake model, which has highly efficiency but serious dependence on empirical parameters and cannot include air viscosity effect, furthermore, the aerodynamics calculated in free wake model are based on the lifting-line theory with the drawback in air load capturing and flow field describing, especially for the characteristics of transonic flow.

The full-potential equations are based on the potential flow theory, but the result computed by this method is usually larger than the real one as it ignored the effect of wake.