Pylon trailing edge blowing effects on the performance and noise production of a pusher propeller

Abstract

This paper discusses a study of the Effects of pylon trailing edge blowing on pusher propeller performance and noise emissions. Experimental investigations were performed in a low speed open jet wind tunnel, using a powered propeller model and a generic pylon model. The pylon blowing system was integrated in the aft part of the pylon, and consisted of a novel “Uniform Blowing Rod” aimed at providing a uniform outflow from its outlet. The numerical analyses were executed using a combination of the existing propeller lifting line code XROTOR and a set of analytic methods from the literature combined to assess the Effects of pylon installation on the propeller performance and noise emissions. Measurements of the velocity distributions in the blown pylon wake showed that application of the blowing system reduced the integrated velocity deficit by up to 60% compared to the unblown configuration. The mixing of the external and blown flows was not optimal, as a result of which the blown wake profiles did not become completely uniform. Evaluations of the propeller forces and moments showed that the Effects of installation on the time-averaged propeller performance are small, with differences of at most 2% for advance ratios below 1.4. Furthermore, excellent agreement was obtained between the computed and measured performance for the isolated propeller. With respect to the propeller noise emissions it was observed that installation of the pylon upstream of the propeller strongly increases the noise levels. Depending on the propeller operating point, noise penalties of up to 15 dB were measured. The application of pylon blowing clearly reduced the propeller noise emissions over the entire advance ratio range, with reductions of up to 7 dB compared to the unblown case. The noise reductions were highest at the highest blowing rate, indicating that the most effective blowing rate might not have been reached.