Influence of Detached Boundary Layers and Surface Roughness on Cavitation Inception

The physics of cavitation inception is a highly complex phenomenon that is influenced by factors like the local pressure minima and presence of microscopic nuclei. Previous studies and recent experimental works have talked about the presence of adverse pressure gradients and recirculating flow for the upstream microbubble migration and eventual growth by gas diffusion. The studies have also noted that the cavitation events incept in the free shear layer downstream of the reattachment. A series of high-speed imaging experiments were carried out in a mini-scale water tunnel incorporating a Venturi geometry. The flow field was examined, and inception events were tracked to investigate the cavitation process in detail. In the case of a detached/separated boundary layer, the primary inception events appeared to occur at the start of the shear layer away from the wall and the inception events were seen confined to the separation bubble. Small scale inception events were noted downstream of the reattachment. The effect of surface roughness was also investigated, and the results are discussed. The contribution of roughness elements in sustaining cavitation is also presented.