Scaling effects on cavitation noise.

In order to clarify the scaling effects on cavitation noise, the acoustic power of the noise, the power spectra, and the corresponding cavitation characteristics for four similar flat-hydrofoils with chord length C from 53 mm to 160 mm was measured. The measurements were performed under similar conditions at the same flow velocity and at the same cavitation-nuclei size-distribution in test water. The scaling effects on the acoustic power I was determined to be a power law: I alpha Cn in the ultrasonic range in a wider cavitating range. The exponent n took the value 1.4 or 6.2, depending on the types of cavitation. The exponent 1.4 corresponded to the initiation state of fine-bubble- cavitation distributed spanwise within the laminar separation bubble near the leading edge, while the exponent 6.2 corresponded to a transient cavitating state accompanied with erosive bubble-clouds or vortex cavitation, "abrupt cavity separation", and shedding of large bubble clouds. (A)