An experimental investigation of cavitation inception and development on atwo-dimensional hydrofoil

The cavitation inception (and desinent) angles at given cavitation numbers, the velocity distribution, and the resulting pressure coefficient, togethe r with the sheet cavity lengths developing on a hydrofoil surface, have bee n investigated experimentally for a Reynolds number ranging between 0.4 x 1 0(6) and 1.2 x 10(6). It is shown that the cavitation inception land desine nt) angle decreases progressively when the Reynolds number increases and te nds to be close to the theoretical (inviscid) value when the Reynolds numbe r is larger than 0.8 x 10(6). The magnitude and the position of the minimum surface pressure coefficient, inferred from the velocity distribution meas ured at the leading edge, were shown to be dependent upon the Reynolds numb er as well. An investigation of the cavitating flow velocity field upstream of the cavity and on the cavity surface showed that the pressure in the ca vity was very close to the vapor pressure. The detachment location of the c avity was found to occur very close to the leading edge (at about one hundr edth of the foil chord for both Re = 0.4 x 10(6) and Re = 0.8 x 10(6)). The length cavities measured from flow visualizations exhibited a sudden chang e for a Reynolds number passing from 0.7 x 10(6) to 0.8 x 10(6) with a give n angle of incidence (alpha = 6 deg) and cavitation number (sigma = 1.3). P hotographs of the sheet cavity show that the cavity length can be inferred also from the extent of the region for which the pressure coefficient is cl ose to the cavitation number. It was shown to have the values I/c approxima te to 0.03 for Re = 0.4 x 10(6) and I/c approximate to 0.06 for Re = 0.8 x 10(6) and sigma = 1.8 with the latter value very close to the value obtaine d from flow visualizations. Photographs of the cavity show that the increas e of the cavity length is coupled to the migration, towards the leading edg e, of a transition point on the cavity surface when the Reynolds number inc reases.