Analysis of swirl recovery vanes for increased propulsive efficiency in tractor propeller aircraft

In this paper we address a preliminary assessment of the performance effects of swirl recovery vanes (SRVs) in a installed and uninstalled tractor propeller arrangement. A numerical analysis was performed on a propeller and a propeller-wing configuration after the SRVs were optimized first in a separate process. The SRVs are essentially designed to recover the swirl in the rotor slipstream, thereby increasing the propulsive efficiency. To confirm the main flow effects of the SRVs, a separate windtunnel study was performed on a single-rotating propeller model in the large low-speed windtunnel. A steady RANS-based numerical analysis showed that the application of SRVs in a propeller-only model may lead to an increase of propulsive efficiency in the order of 2 %. In case of the SRVs in a representative tractor propeller-wing configuration, the positive effects are reduced due to the swirl recovery effect of the wing and the upwash effect in the SRV plane. The latter requires an optimization per SRV blade which was not performed in this particular study. In de experimental study performance data of the propeller were acquired with a rotating shaft balance. Furthermore, Particle Image Velocimetry PIV measurements in the slipstream of the propeller with and without SRVs substantiated the efficacy of the vanes in reducing the swirl in the propeller slipstream. Reductions of 50% in the swirl kinetic energy was observed at a medium thrust settings.