Experimental investigation of inception cavitating flows around axisymmetric bodies with different headforms

Experiments have been performed to study the inception cavitation phenomena in the separated flows adjacent to two axisymmetric bodies whose forebodies are blunt and conical, respectively. A high-speed video camera was used to visualize the dynamic process of incipient cavitation, and the PIV (Particle imaging velocimetry) technology was applied to measure the velocity field, the vorticity and turbulence fluctuations under non-cavitation and inception cavitation conditions. Observations suggest that incipient cavities around the two axisymmetric bodies have the similar onset appearance but different development patterns and cycles with different inception cavitation index. Also, it is found that incipient cavities are always located within the separated vortex upstream the reattachment point during the whole dynamic process, and the scale of separation vortex greatly influences the positions where incipient cavities generate and collapse. Measures of the turbulence fields show that the distribution of vorticity can be changed by unsteady incipient cavities, and inception cavitation causes slight uniformity of velocity in shear layer and conspicuous increase of turbulent fluctuations. Compared to that of the conical headform, inception cavitation around the blunt headform presents more vortical traits and turbulence fluctuations.