A Study of the Influence of Gas Nuclei on Cavitation Scale Effects in Water-Tunnel Tests

The gas content of water employed in a cavitation tunnel is known to influence the conditions under which cavitation will be initiated. This study gives emphasis to the importance of the portion of the gas content which is in the form of free-gas bubbles. it is shown that these cavitation nuclei are inhibited from forming in existing types of water tunnels and that such inhibition may contribute to scale effects in model testing. The report describes a new modification to tunnel construction that promotes and controls the presence of gas nuclei in the water. The increased concentrations of nuclei provided by the new tunnel were evaluated by very promising new instrument developed specifically for such measurements. Scale effects evident in cavitation-inception tests in other tunnels were substantially reduced in comparable tests in the new tunnel.