Nucleation effects on hydrofoil tip vortex cavitation

Tip vortex cavitation inception about an elliptical planform, NACA 0012 hydrofoil is investigated in cavitation tunnel flows in which cavitation nuclei are deplete and abundant. Tests were conducted at fixed Reynolds and cavitation numbers. The onset, or inception, of cavitation was induced by increasing the angle of incidence and behaviour was recorded photographically and acoustically. Cavitation inception occurred at a higher incidence in the deplete case compared with the abundant due to fewer weaker nuclei. It also occurred within a small incidence change for the deplete case, with the appearance of a continuous, cavitating vortical flow structure. Whereas for the abundant case, inception was intermittent, occurring across a larger incidence range. This was associated with individual nuclei activation events increasing in frequency with increasing incidence. Sound pressure levels increased with inception and cavity development but reduced to a local minimum once the cavity attached to the hydrofoil, increasing thereafter with incidence. Overall sound levels were higher for the abundant case than for the deplete case.