Scaling of Gas Diffusion Into Limited Partial Cavities

Bubbles populations in the wake of a partial cavity resulting from gas diffusion were measured to determine the noncondensable gas flux into the cavity. The diffusion rate is related to the dissolved gas content, the local cavity pressure, and the flow within and around the cavity. The measurements are used to revisit various scaling relationships for the gas diffusion, and it is found that traditional scaling that assumes the presence of a gas pocket overpredicts the gas diffusion. A new scaling based on diffusion into the low void fraction bubbly mixture within the partial cavity is proposed, and it is shown to adequately scale the observed production of gas bubbles for dissolved air saturation from 30% to 70% at 1 atm, limited cavities on the order of 0.3-3 cm in length at a free-stream speed of 8 m/s (sigma = 2.3-3.3 and Reynolds number based on the cavity length of order 10(5)).