Experimental investigation of the helicopter blade tip shape effects on aerodynamic performance and tip vortex characteristics

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2019
Uluocak, Sinem
This study experimentally investigates the effects of different rotor blade tip shapes on the rotor aerodynamic performance and the tip vortex characteristics in hovering flight. Force, torque and flow field measurements were performed on a 1.3 m diameter 5-bladed model rotor for four different blades: rectangular (RECT), anhedral (ANHD), tapered-swept (TAPER) and tapered-swept-anhedral (TSA). Thrust and torque measurements show that all tip modifications have a positive effect on the aerodynamic performance when compared to the RECT tip configuration especially at low blade loadings. Overall, the ANHD tip configuration gives the best aerodynamic performance at high blade loadings. It reaches a maximum figure of merit (FOM) value of 0.67 and provides a FOM improvement of approximately 0.03 compared to the RECT blade at the tip Mach number (Mtip) of 0.3. Phase-locked particle image velocimetry measurements were conducted at 6◦ intervals between 0◦ -72◦ phase/wake ages at the selected pitch angle of 16◦ and Mtip = 0.4. It is observed that tip modifications change the tip vortex trajectory by increasing radial convection speed and decreasing axial convection speed. ANHD reduces the maximum vortex tangential velocity up to 20%; the TAPER and the TSA reduces it up to 30%. The minimum tip-vortex circulation level is achieved in the case of the ANHD blade, which is in agreement with the highest FOM obtained with this blade.

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Citation Formats
S. Uluocak, “Experimental investigation of the helicopter blade tip shape effects on aerodynamic performance and tip vortex characteristics,” M.S. - Master of Science, Middle East Technical University, 2019.