Research on Prevention of Root Erosion by Fin

（一）.本项目的目的：高速船舶和工艺品的螺旋桨轴安装在船舶船体上，并与船体表面成一定的倾斜角，螺旋桨的来流成为斜流。众所周知，这种类型的流动在螺旋桨的一转期间由于入流角的大变化而在螺旋桨的根部附近产生有害的非定常空泡，并且在斜流中工作的螺旋桨上的浑浊空泡经常在螺旋桨根部附近引起严重的侵蚀，即使在速度试验期间也是如此。在以往的研究中，通过在螺旋桨前安装小鳍片，可以显著地减少根部的冲蚀。另一方面，这些翅片的优化理论设计方法尚未开发。本项目的目的是开发小鳍螺旋桨的优化理论设计工具，并为理论分析和设计工具获得可靠的验证数据。（二）、 ...更多信息 项目进展：为了开发理论分析方法和设计工具，首先，不仅通过油漆侵蚀试验，还通过使用100，000 fps左右的超高速摄像机进行的流动显示，检查了鳍对螺旋桨性能和空腔塌陷行为的影响。为了验证理论分析工具的有效性，采用激光多普勒测速仪（LDV）测量了几种鳍片结构的前鳍螺旋桨的流场，并在第二年设计制造了一种新的螺旋桨和一种鳍片。对该螺旋桨和另一种螺旋桨的性能进行了无鳍和有两种鳍的几种组合的测量。本文研究了在均匀流和10 °斜流条件下，翼片对螺旋桨根部空泡特性的影响。建立了螺旋桨在斜流中工作的两种分析方法，即时域严格面元法和频域实用面元法。对几种鳍形的螺旋桨进行了空泡观测和冲蚀试验。通过对桨叶根部腐蚀试验结果的数据分析和桨叶压力分布的计算，得到了桨叶根部腐蚀与桨叶结构参数（包括无桨叶结构）之间的相关系数。最后提出了带抗根蚀鳍螺旋桨的合理布置设计方法。少

(1). Purpose of the Present Project:The propeller shafts for high-speed ships and crafts are equipped to the ship hull with an inclined angle to the hull surface and the incoming flow to the propeller becomes an oblique flow. It is well known that this type of flow generates detrimental unsteady cavitation near the root of propellers due to large variation of inflow angles during one revolution of the propeller and cloudy cavitation on the propeller working in the oblique flow often causes severe erosion in the vicinity of propeller root even during the speed trial. In the previous research, the root erosion was reduced remarkably by equipping small fins in front of the propeller. On the other hand, no optimum theoretical design methods of these fins have not been developed yet. This project has been carried out to develop the optimum theoretical design tools for the propeller with small fins and to acquire reliable validation data for both theoretical analytical and design tools.(2). … More Progress of the Project:In order to develop the theoretical analysis method and the design tools, first of all, the effects of the fin to the propeller performance and to the cavity collapsing behavior were examined by not only paint erosion test but also flow visualization using an ultra-high speed video camera around 100,000 fps. The flow field around the forward fin propeller with several configurations of fins was measured by Laser Doppler Velocimeter (LDV) to obtain the validation data for theoretical analytical tools.In the second year of the present project, a new propeller and a fin were designed and manufactured. The performance of this propeller and other one was measured without fins and in several combinations with two kinds of fins. The effects of the fins on the cavitation characteristics around the root of the propellers were examined not only in uniform flow but also in the 10deg-oblique flow. Two analytical methods for the propellers working in the oblique flows were developed, which are the rigorous surface panel methods in time domain and the practical surface panel methods in frequency domain. Cavitation observation and erosion tests were carried out on the propellers with several fin configurations. Data analysis on the erosion test results and the computations on the blade pressure distribution around the root of propellers was performed to find the correlation factor between the erosion severity and the fin-propeller configuration including the cases without fin. Finally the reasonable design method for the optimum arrangement of the propeller with anti-root erosion fins has been developed. Less