Experimental investigation of the impact of a propeller on a streamwise impinging vortex

By employing a wing-tip vortex impinging onto a propeller, the impact of the propeller on this vortex is studied with the help of Particle Image Velocimetry measurements. The effects of the propeller on the vortex are compared in the flow fields in the vicinity of the blades, i.e. one plane upstream and one plane downstream of the propeller. The meandering of the vortex downstream of the propeller increases by approximately one order of magnitude with respect to that upstream of the propeller. The circulation of the downstream vortex is at the same level as the upstream vortex, and this means the downstream vortex still has the potential to influence the airframe further downstream. As the vortex impinges at different radial positions of the propeller, the stretching effect depends on the local thrust of the propeller, which is different from the case with a vortex impinging on a steady wing. The Proper Orthogonal Decomposition analysis shows that the first and second modes of the flow upstream of the propeller are induced by the blade passing, whilst the third and the fourth modes are induced by the vortex meandering.