Qualitative investigation of a propeller slipstream with Background Oriented Schlieren

Abstract

The Background Oriented Schlieren (BOS) method has been used to qualitatively identify the (variation of) density gradients in the helical structure of a propeller slipstream. The helical structures are identified for two sideslip angles. In contrast to standard BOS correlations between exposures and a reference image, two exposures at a given time interval were cross-correlated. This revealed a more clear description of the propeller slipstream as it determines the variation of the density gradient during this interval. It enhances the visualization of the helical structure of the propeller slipstream. Based on the visualizations of the blade tip vortex trajectories the propeller slipstream contraction can be estimated.