Experimental and theoretical studies of the effect of gas content on unsteady cavity flows

A partially cavitating two dimensional hydrofoil was oscillated in pitch while air was bled into the cavity at a controlled rate. By varying the ambient pressure and air flow rate simultaneously, a constant ventilation number was maintained for a series of cavity air partial pressures. Unsteady forces and cavity pressures were measured, and photographs taken. It was found that cavity air caused fluctuating cavity pressures, and tended to stabilize cavity length. Its effect on force coefficients was relatively modest. These trends were also found from a parallel theoretical investigation in which a computer program which predicts unsteady cavitation of 2-D foils was modified to allow for cavity gas.