The Effect of Water Quality Characteristics on Cavitation Noise
This study investigated the effects of seawater on cavitation noise using a water jet test, a two-dimensional wing test, and a three-dimensional wing test. A model propeller cavitation test was conducted in a cavitation tunnel using seawater, in order to determine the effects of propeller cavitation more precisely. In the cavitation tests, measured propeller performance for both cavitation noise inception and desinence, as well as the cavitation noise spectrum (see, for example, figure 7). On the basis of the results of the present propeller cavitation test and tests that were carried out previously, we discuss how to control the water quality in the cavitation tunnel to reproduce the cavitation phenomena, especially cavitation noise, in seawater (see, for example, figure 9).
Effect of Surface Material on the Cavitation Erosion Noise: Experimental Investigation
Cavitation includes the occurrence, growth and collapse of vapor bubbles in a liquid. Cavitation noise is the sound uttered during the cavitation progress, and it is mainly induced by the collapse of the bubbles. Under certain presuppositions, the micro-jet and micro-shockwave can be produced when the bubbles collapse. The impact of the microjet and micro-shockwave on the surface of material is strong enough to damage the structure of the material and finally erosion takes place. Accordingly, compared with cavitation, the sound emitted during the cavitation erosion progress has a more source that is induced by the vibration of the solid surface when it is attacked by the micro-jet. In this work, the effect of the surface material on the cavitation erosion noise has been studied. Spectrum characteristics obtained for different metal materials: stainless steel, aluminum bronze, bronze, brass (in the same experimental conditions) has also been presented in this paper. The purpose is to validate the contributions of the impact noise to the cavitation noise.
Freestream Nuclei and Traveling-Bubble Cavitation
Traveling-bubble cavitation inception tests were conducted in a 30.48 cm water tunnel with a Schiebe headform. A computer code was developed to statistically model cavitation inception on a Schiebe headform, consisting of a numerical solution to the Rayleigh-Plesset equation coupled to a set of trajectory equations. Using this code, trajectories and growths were computed for bubbles of varying initial sizes. An initial off-body distance was specified and the bubble was free to follow an off-body trajectory. A Monte Carlo cavitation simulation was performed in which a variety of random processes were modeled. Three different nuclei distributions were specified including one similar to that measured in the water tunnel experiment. The results compared favorably to the experiment. Cavitation inception was shown to be sensitive to nuclei distribution. Off-body effect was also found to be a significant factor in determining whether or not a bubble would cavitate. The effect of off-body trajectories on the critical bubble diameter was examined. The traditional definition of critical diameter based on the minimum pressure coefficient of the body or the measurement of liquid tension was found to be inadequate in defining cavitation inception.