Pusher-Propeller Installation Effects in Angular Inflow

Pylon-mounted pusher propellers su_er from installation e_ects due to the interaction between the pylon and the propeller. The impact of angular inow on these installation e_ects was quanti_ed at the Large Low-Speed Facility of the German-Dutch wind tun- nels (DNW-LLF). Particle-image-velocimetry measurements showed that the pylon wake's width and velocity de_cit were hardly a_ected by the introduction of a six-degree sideslip angle. Application of pylon trailing-edge blowing reduced the integral velocity de_cit in the wake by up to 65%. Evaluations of the surface pressures on the blades con_rmed the sinusoidal loading behavior in angular inow and the impulsive loading peak due to the pylon-wake encounter. The circumferential velocity components induced by the pylon tip vortex strongly a_ected the steady-state propeller performance by modifying the e_ective advance ratio sensed by the blades. Increased performance was measured when the rota- tion direction of the pylon tip vortex was opposite to that of the propeller. Angular inow a_ected the propeller noise emissions due to the resulting unsteady blade loads and the circumferential variation of the e_ective Mach number of the blade sections. The instal- lation of the pylon added a noise source due to the unsteady blade loads caused by the pylon-wake encounter. Depending on the sideslip angle, application of blowing eliminated a large part of the installation noise penalty, despite remaining non-uniformities in the blown wake pro_les