非定常空泡闭合区域最大压力的理论研究

A THEORETICAL INVESTIGATION ON THE MAXIMUM PRESSURE OF THE UNSTEADY CAVITY CLOSURE POSITION

当物体在流体中高速运动产生空泡时,空泡通常以回射流的形式闭合在物体表面上,并在闭合位置对物体表面产生流体超压.在物体表面上的空泡闭合位置一般不是固定的,其位置根据物体运动速度的变化、空泡压力的变化及重力场中的位置等因素而在物体表面发生快速移动,在非对称情况下,这种移动超压会极大影响运动物体的稳定性.基于势流理论研究了重力场中非定常垂直空泡闭合区域中最大压力的存在位置,推导了最大压力的理论公式,揭示了最大压力与空泡发展速度之间的关系,证明了最大压力点的两个特殊流体性质.最后设计了测量空泡闭合区域最大压力的验证性试验,并将理论计算结果与试验测量结果进行了对比,验证了理论研究结果.

The cavity closes on the body surface with a re-entry jet at its rear when the body moves with a high speed and induces a cavity in the fluid. The re-entry jet at the closure position of the cavity causes the overpressure on the body. The closure position moves with a considerable speed when the cavity is in the gravity field or when the body velocity or the pressure in the cavity varies. The unsymmetrical distribution of the moving closure position with overpressure arouses significant effect on the motion stability of the body. As far as we know, no theoretical researches about overpressure on the moving closure position owing to the unsteady of the cavity have been reported in literature. In this paper, based on the theory of the potential flow, the position of maximum pressure in closure region of unsteady cavity in gravity field is investigated, and the theoretical formula of maximum pressure is presented, which reveals the relation between the maximum pressure and the developing speed of the cavity. Two special fluid characters of maximum pressure are proved. Finally, a verification experiment is designed and performed for measuring the maximum pressure at the closure position, and the comparison is finally performed between the results of the theoretical formulation and the experiment, which confirms the theoretical approach in this study.