Effect of a Winglet on Open Rotor Aerodynamics and Tip Vortex Interaction

Abstract

The open rotor is being re-considered as an alternative to the advanced turbofan in order to address growing pressure on the aviation industry to reduce fuel consumption and cut carbon dioxide emissions. Meeting future community noise targets is likely to be a challenge for the open rotor, however, and novel noise reduction technology will be required. In this paper, a blade tip winglet on the front rotor is investigated using steady RANS computations for reducing tip vortex interaction noise at takeoff. Only the front rotor row is analysed with the intention being to gain a first insight into the aerodynamics of a blade with a winglet. For this reason, the design of the winglet has not been optimized. Notwithstanding, the winglet design investigated here is predicted to give reductions in maximum tip vortex swirl velocity of order 30% under a takeoff condition representative of modern open rotor operation. The cause of this reduction is shown to be consistent with shedding of bound circulation over a greater spanwise distance. At cruise, the winglet improves the propeller efficiency of the front rotor by 0.4%. A control volume analysis of the lost propeller power shows that approximately half of the propeller efficiency benefit is due to reduced entropy generation associated with the formation of the tip vortices, and a reduction in vortex swirl kinetic energy.