CFD-CSD coupled study in the BVI characteristics of a saw-tooth blade planform

Numerical studies have been done to investigate the effects of forward-backward swept saw-tooth blade planforms on blade-vortex-interaction phenomena. A well-documented and publicly available HART-II rotor was used as the baseline rotor, and the shape was parametrically modified. The baseline rotor was analyzed using CFD-CSD loosely coupled methodology with a posteri acoustic analysis. Parametric analyses were performed with the blade motion obtained from the baseline rotor in order to isolate the shape effects from the blade motion. As expected, the optimized saw-tooth blade form leads to oblique BVIs, and the interaction spreads the blade-vortex interaction over a longer time period. The optimized planform is also found to reduce peak blade loads over the second and third quadrants. Consequently, the tip vortex strength and the impulsive effect of the blade-vortex interaction were reduced. A peak noise reduction up to 3 dB at selected observed locations was predicted by the present combined CFD-CSD-CAA analysis, relative to the baseline rotor, for the same thrust and moments at the hub, but the required power was increased.