Aerodynamic and Aeroacoustic Performance of a Propeller Propulsion System with Swirl-Recovery Vanes

Swirl-recovery vanes (SRVs) enhance propulsive efficiency by converting the rotational kinetic energy in a propeller slipstream into additional thrust. This paper discusses the aerodynamic and aeroacoustic impact of the installation of a set of SRVs downstream of a single-rotating propeller. Experiments were carried out in a large low-speed wind tunnel, while simulations were performed by solving the Reynolds-averaged Navier–Stokes equations. Favorable comparisons between the experimental and numerical slipstream data validated the simulations, which predicted a maximum propulsive-efficiency increase of 0.7% with the current design of the SRVs. This can be improved further by optimizing the SRVs' pitch distribution. The upstream effect of the SRVs on the time-averaged propeller performance was negligible. Yet, small but systematic unsteady propeller loads were measured with a peak-to-peak amplitude of at most 2% of the time-averaged loading, occurring at a frequency corresponding to the five SRV passages during one revolution. The downstream interaction was one order of magnitude stronger, with unsteady loading on the SRVs with a peak-to-peak amplitude of about 20% of the time-averaged load. The interaction mechanisms caused an increase of the tonal noise levels of 3 to 7 dB, with the noise penalty decreasing with increasing propeller thrust setting.