超空泡内部流动机理及相关测试技术研究

The research of cavitation is still one of the hotspots in present fluid mechanics study. The understanding of the mechanism of the supercavitation is very important for the research and development of the high-speed vehicle. Supercavitation is a dynamic process and the flow is a complex phenomenon. In previous studies of the flow physics of the supercavity, digital strobe photography was usually utilized to describe cavity shape. Laser Doppler Velocimetry (LDV) was often used to measure the velocity of the point concerned and pressure transducer was also utilized to obtain the pressure caused by the cavitation. However, the results obtained by the three measurement techniques for measuring cavitation mentioned above are qualitative or single-point survey. To study the flow physics of the supercavity generated by the cavitator, it is very important to use the Particle Image Velocimetry (PIV) technique to obtain the whole velocity distribution inside the supercavity. In the present proposal, fluorescence will be used as the seeding particles and injected into the inside of the supercavity through a pipe. From the analysis of the experimental results, a new mechanism of the supercavitation will be proposed. It is difficult to control the underwater high-speed vehicle. The understanding of the flow inside the supercavitation will provide a theory basis for the development of a control method which can be implemented on the underwater high-speed vehicle.

空化研究目前仍然是流体力学研究的热点问题之一，尤其是近年来对超空化的研究更加引起人们的关注，主要原因是超高速航行体（鱼雷、潜艇等）的研发需要对超空泡内部空化场的流动机理过程进行深入的研究。超空化本身具有丰富的动力学过程和复杂的流动现象，目前对超空泡的观察主要是基于高速摄影的流动显示定性观察，而超空泡内部速度场的实验测量主要采用LDV单点测量，很难提供整个测量区域的瞬态流动信息。本项目将利用申请人开发的壁面粒子播撒技术解决空泡内流场示踪粒子的播撒问题，在空泡水筒中，采用荧光颗粒作为示踪粒子，运用PIV测试技术对超空泡内外流场进行同时测量，深入开展超空泡流动结构的时空演化规律研究与分析，揭示超空泡的流动机理。超高速航行体的一个主要问题是运动方向控制困难，通过流动控制，改变超空泡内部流动结构分布，进而为超高速航行体的运动方向控制问题提供理论基础。

超空泡航行体主要是在水下航行体表面形成超空泡从而大幅降低水下航行体的阻力，提高航行速度。目前，对于超空泡的流动机理仍不清楚，尤其是缺乏空泡内部流场的流动信息。本项目在国际上首次尝试用PIV测试技术对超空泡内外流动结构及其内在机理进行系统研究，围绕超空泡内部流场的定量测量和超空泡流动机理等方面开展研究。建立超空泡内部流场的PIV测试技术，掌握超空泡内部的流动结构、演化与特征，对超空泡形态影响要素进行分析研究，为超高速航行体的方向控制提供依据。研究发现：当来流空泡数大于1.33时，超空泡内部流动以泄流式为主。当来流空泡数为1.26甚至更低时，超空泡内部流动以环流式为主。泄流式可以通过改变通气量来改变超空泡尺度的大小，而环流式的超空泡更加稳定，即使改变通气量，也很难通过改变超空泡流动形态进而对超空泡流动进行控制。