Pressure and noise induced by a cavitating marine screw propeller: Dissertation

A method of evaluating the intermittent propeller blade fixed cavitation and shedding of free cavitation bubbles is presented. The number and size of free, spherical cavitation bubbles are related to the variation of propeller blade attached cavitation. The beta type probability density distribution of the initial bubble size is proposed. This distribution is normalized with respect to the sheet cavitation thickness. The effect of the simplifications in the dynamic model of the cavitation bubbles on their collapse downstream of partially and fully cavitating hydrofoils is discussed. The method of calculating the low frequency pressures induced by fixed blade cavitation and high frequency broadband noise caused by the collapse of free bubbles in propeller flows is presented. The method yields noise spectra in the frequency range from the blade passing frequency to tens of kilohertz. Computed pressure and noise induced by the cavitating propellers are compared to the values measured in model and full scale experiments. The fractal structure of the bubble cloud and the proposed method of evaluating the collapse of the bubble cloud downstream of the fixed cavities yield noise spectra which correlate well with the experimental results of full and model scale measurements.