三维非定常超空化流动机理研究

It is of both great scientific and military significance to study the mechanism and unsteady characteristics of the supercavitation phenomenon. Under certain circumstance, when the ambient pressure is equal to or less than the saturation vapor pressure, vaporization of water occurs and a giant air bubble encircling the high-speed underwater vehicle can be generated. As a result, the vehicle can also travel at a very fast speed in water as it does in air. In the cavitating flow field, both compressible air and incompressible water exist. In addition, a phase change can cause complex thermophysical processes and the change of density near the wall of bubbles is abrupt. Therefore, it is difficult to conduct accurate simulation of such complicated physical phenomenon by using the current computational fluid dynamics methods. Based on preconditioning techniques, a novel method to solve the cavitating flows with phase change had been developed in the previous project completed by the applicant, in which pressure, velocity and enthalpy were used as the original variables, the cavitation model was replaced with non-physical energy equations, and Roe format was adopted to achieve high precision. In this project, the applicant attempts to use the above-mentioned CFD method to conduct in-depth studies on issues associated with supercavitation including the mechanism of upercavitation flow around an underwater vehicle, the characteristics of mass and energy conversion, the role and influence of energy conversion in cavitation process.

水下高速潜体周围超空化流动机理及非定常特性研究，具有重要的科学意义和国防意义。在一定条件下， 当潜体周围水的压力等于或低于其饱和压力时，水就会发生汽化，产生一个包裹在高速潜体周围的气泡，使得潜体在水下也能像在大气中前进那样快捷如飞。空化流场中，不可压液体与可压气体并存；流场中的相变导致了复杂的热物理过程；汽泡壁附近密度变化巨大,流场不连续。对如此复杂物理现象的准确模拟，传统的计算流体力学方法是有难度的。申请者拟采用前一个培育项目已建立起来的一套解决含相变空化流动问题的新方法,该方法以压力、速度与焓为原始变量，用能量方程取代非物理的空化模型，以预处理方法为基础,采用Roe格式实现高精度。利用该方法详细研究高速潜体周围非定常自然空化流动机理、能量转换在空化过程中的作用及对空化过程的影响。

水下高速潜体周围超空化流动机理及非定常特性研究，具有重要的科学意义和国防意义。在一定条件下， 当潜体周围水的压力等于或低于其饱和压力时，水就会发生汽化，产生一个包裹在高速潜体周围的气泡，使得潜体在水下也能像在大气中前进那样快捷如飞。空化流场中，不可压液体与可压气体并存；流场中的相变导致了复杂的热物理过程；汽泡壁附近密度变化巨大,流场不连续。对如此复杂物理现象的准确模拟，传统的计算流体力学方法是有难度的。.a) 重新梳理含相变两相流动的数学物理方程组. 在求解连续方程与动量方程的同时, 再联立求解能量方程, 采用能够真正反映含相变两相流动过程中能量特性的焓, 建立两相之间的能量转换与传递关系, 比传统的基于空化模型的方法(忽略能量方程)更接近物理本质, 进行细致程序考核。.b) 检查含有相变的两相流场统一的计算方法及相应的状态关系. 以焓、速度与压力为原始变量, 通过相应的数学方法, 检查所构造新的流体力学预处理方法, 完成一套含有相变的两相流体动力学计算方法的建立。.选择压力与焓为基本变量, 建立其他状态参数与压力和焓之间的关系。不管在液体区、气体区, 还是饱和区, 由压力和焓, 都可以唯一确定其他所有的状态参数。进行细致程序考核。.c) 计算方法及计算程序的详细考核与再验证. 利用国外经典的半球头空泡实验数据, 进一步考核与验证程序计算不可压、局部空化及捕获汽液交界面的能力与性能，获得空化时空隙度的云图，并与相同工况下的实验结果比较。