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“Cavitation Inception in Turbulent Shear Layer”
Presented by KARUNA AGARWAL
(Adviser: Prof. Joseph Katz)
The scaling of cavitation inception in a turbulent shear layer generated by a backward-facing step is studied by measuring the pressure distributions as well as flow-nuclei interactions, over a wide range of Reynolds numbers (1.5*10^4 to 1.6*10^5). Time-resolved tomographic PIV is used to get 3D velocity and pressure fields in a 12x7x4 mm region where most of the early cavitation occurs. Data are processed using a constrained cost minimization technique, which establishes a divergence free velocity and curl-free material acceleration fields at a spatial resolution of 200µm. The quasi-streamwise vortices, along which the 1-2 mm wide and over 5 mm long cavities form, are detected using k-means clustering of quantities based on velocity spatial gradients. The pressure minima are preferentially located within these vortices and are strongly influenced by vortex stretching. The duration of the low pressures, as experienced by neutrally buoyant particles, increase with Reynolds number. The durations of low-pressure events for the buoyant nuclei will likely increase if they are entrained by the vortices. Therefore, trajectories of free-stream nuclei are recorded, which show that the bubbles have significantly lower streamwise velocities compared to the flow.