Mitigation of Pusher-Propeller Installation Effects by Pylon Trailing-Edge Blowing

This paper presents an experimental assessment of the working principles of pylon trailing-edge blowing for the mitigation of the interaction between a pusher propeller and its associated pylon. The experiments were performed at the Large Low-Speed Facility of the German–Dutch wind tunnels (DNW–LLF), using a powered propeller model and an upstream pylon equipped with a trailing-edge blowing system. In-flow microphone measurements demonstrated the impact of pylon installation on the propeller’s tonal noise emissions, with increases of up to 16 dB relative to the isolated propeller. Analysis of the unsteady blade pressures showed that this installation effect is caused by the impulsive increase in blade loading during the pylon-wake passage. The efficacy of pylon trailing-edge blowing to reduce the momentum deficit in the pylon wake was confirmed by stereoscopic particle-image-velocimetry measurements between the pylon and the propeller. Consequently, application of the pylon-blowing system alleviated the pylon-installation effects at the source. At an intermediate thrust setting, the root-mean-square of the blade-load fluctuations due to the wake encounter was reduced by up to 60%, resulting in noise emissions approximately equal to those recorded for the isolated propeller.