LES of vortex pair interaction and analysis of cavitation inception

Cavitation inception due to vortex pair interaction is commonly observed in the wakes of propeller blades, in jets, and in other shear layer flows. We use LES to study the interaction between a pair of unequal-strength counter-rotating vortices in the wake of two hydrofoils at Re = 1.7 million. The LES results are compared to the experiment. In the near wake regime, we observe the axisymmetrization of both the cores and their rotation about a common center. Subsequently, Crow instability develops on the weaker core resulting in sinusoidal perturbations. Growth of the instability causes vortex stretching and wrapping of the weaker core around the stronger core. During this process, the weaker core pressure drops below vapor pressure making it a potential site for inception. Core size measurements reveal that core size reduction alone is not sufficient to cause the observed drop in pressure. We observe a strong axial jet near the inception location which could lead to a further drop in core pressure. We also discuss the correlations between core pressure and axial strain rates and axial vorticity.