FUNDAMENTAL RESEARCH IN HELICOPTER ROTOR BLADE - VORTEX INTERACTION MODELING

To improve the understanding of flow phenomena involved in helicopter rotor vibration and noise, blade-vortex interactions (B VI) were investigated analytically and experimentally by modeling two dimensional vortex encounters with an airfoil section. Analytically, the unsteady flow and its interaction with a lifting airfoil were calculated using a scheme which employs conformal transformations and clusters of discrete vortices. In the laboratory, a pitching NACA 0012 was used to generate vortices which interact with a “target” airfoil positioned downstream. Measurements using Laser Doppler Velocimetry (LDV) were obtained in the flow field surrounding the target airfoil. The instantaneous chordwise pressures calculated by analysis were compared to the experimental data and found to be in good qualitative and quantitative agreement. The flow field measurements, reported here, provide an insight into the mechanism of blade-vortex interaction effects and are sufficiently detailed to be the data base for the validation of computational fluid dynamics methods by which practical BVI alleviation concepts can be defined.