キャビテーションを考慮したプロペラ設計法の研究 : 第2報 : 振動・騒音・壊食の考慮
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n this paper, from the viewpoint of accurate consideration of unsteady cavitation at the propeller initial design stage, a method to estimate vibration (surface force), noise and erosion, is described. For this study, systematic cavitation tests were conducted in four different wake fields using four kinds of propellers, which have different blade section profiles (reported in the previous paper^<1)>)) and blade areas. The primary results obtained from the tests are as follows ; (1) Surface force is strongly influenced by the gradient of wake fraction in the circumferential direction. (2) Noise, and erosion are closely related to the occurance of cloud cavitation, which is considered to be connected with the amount of cavity volume. (3) In order to reduce surface force, noise and erosion, the improvement of blade section profile is more effective than an increase in blade area. Based on the above experiments, a practical estimation formula of cavity volume is proposed. In the formula, the attack angle variation of corresponding two-dimensional wing, derived from the unsteady lifting surface theory^<11)> is introduced. And cavity volume is assumed to be in proportion to the modified attack angle, in which cavitation unsteadiness is considered in a simplified manner. Using the estimated cavity volume, propeller induced fluctuating pressure is calculated by Holtrop's formula^<16)>. And it is found that the calculated values of fluctuating pressure agree well with the experiments. Then, for the convenience of applying the results to the propeller design process, two simple parameters are proposed based on following ideas ; (1 ) Fluctuating pressure is estimated by the product of maximum cavity volume and the maximum second differential coefficient of attack angle at each radius position. (2) Noise, and erosion 'are estimated by the product of maximum cavity volume and the maximum first differential coefficient of attack angle at each radius position. Experimental results can be explained well by these newly proposed design parameters.
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