Bionic passive flow control of blade tip vortex

The blade tip vortex is a primary contributor to helicopter blade vortex interference noise. The effects of wave crest number, wave crest amplitude, and bottom-to-top ratio on the suppression of the blade tip vortex were investigated through numerical simulations under an incoming flow at Mach 0.3. The results show that a pinnately crested bionic blade tip can effectively suppress the formation and development of the tip vortex. The peak vorticity at the vortex center is reduced by 49.6%, and the vortex core diameter is expanded by 58.3%. However, a minor degradation in the aerodynamic performance of the blade tip is observed. Increasing the wave crest amplitude and number enhances the suppression effect on the tip vortex. The influence of the bottom-to-top ratio on vortex suppression is dependent on the specific design of the wave crest structure. The primary mechanism by which the feather-like bionic tip suppresses the tip vortex involves the interaction between the backflow within the concave cavity of the wave trough and the main flow. This interaction creates low-velocity regions and secondary vortices near the tip, thereby inhibiting tip vortex development.