The incipient cavitation of a pair of unequal strength counter-rotating vortices undergoing the long-wavelength Crow instability is examined with high-speed video, acoustic measurements and volumetric particle tracking velocimetry. This work expands upon the previous studies of Chang & Ceccio ( J. Acoust. Soc. Am. , vol. 130, 2011, pp. 3209–3219) and Chang et al. ( Phys. Fluids , vol. 24, 2012, 014107). Volumetric velocimetry results presented by Knister et al. ( J. Fluid Mech. , 2026) were used to predict the core pressures of the stretched secondary vortices. These data are combined with free-stream nuclei measurements to predict the rates of cavitation inception, which compared well with the directly measured inception rates. The acoustic emissions of incipient cavitation events are also related to the vortex properties and the nuclei content of the water. The reduced pressure in the stretched vortices is shown to be related primarily to the reduction in the core radius of the secondary vortex and not due to axial jetting or straining. The measured vortex dynamics indicates that the process leading to the pressure drop in the secondary vortex core is a transient process but not more rapid than the development of the Crow instability. In conclusion, these results show that a relatively simple model of cavitation inception in a stretched secondary vortex captures the essential physics connecting the nuclei population and the underlying vortical flow field, enabling prediction of the resulting observed inception rates. These results also indicate that the reduced pressures in vortical flow leading to inception are primarily due to the reduction in the core of the vortices and not due to substantive axial jetting. The pressure drop in the vortex cores is accordingly a transient process, but despite the appearances of cavitation inception it does not proceed faster than the development of the Crow instability in the secondary vortices.
Knister et al. (Tue,) studied this question.