环形槽对通气空泡融合的促进作用分析

航行体出水过程中肩部的自然空化将影响航行体的载荷分布及出水姿态,工程上常采用肩部开孔通气的方式改善航行体表面的力学环境, 进而解决此类问题.本文针对水下航行体通气空泡周向融合效果不理想问题, 基于有限体积法,采用VOF (volume of fluid)多相流模型和动态铺层的动网格技术,数值研究了排气孔下游增加小尺度环形凹槽促进空泡融合的作用机制,以及不同发展阶段、不同工况下环形凹槽对空泡融合的促进作用. 结果表明,凹槽可以有效改善通气空泡的融合效果.运动坐标系下来流经过环形凹槽时因为流动膨胀发生了边界层的流动分离,其诱导产生的卷吸作用一方面迟滞了空泡的轴向发展,促进空泡产生周向尺寸更大的剪切涡并沿周向膨胀发展,另一方面将部分通气气体吸入环形凹槽,吸入槽内的气体通过挤压破碎实现了周向融合,且槽内融合气泡溢出下泄促进融合边界上移. 此外,凹槽可以通过改善空泡内部的流动状态,使空泡的形态和内部压力在不同工况下都更加稳定. 

ANALYSIS OF THE PROMOTING EFFECT OF ANNULAR GROOVE ON THE COALESCENCE OF VENTILATED CAVITY

The load distribution and the water-existing attitude of the vehicle will be affected by the natural cavitation on the shoulder of vehicles during the water-exit process. In engineering, active ventilation by opening vent at shoulder is often employed to improve the mechanical environment of vehicle surface so as to solve such problems. This article is aimed at solving the problem that the ventilated cavity circumferential coalescence of underwater vehicles is unsatisfactory. Using the VOF (volume of fluid) multi-phase flow model and dynamic grid technique of dynamic layering based on finite volume method, the mechanism of adding a small-scale annular groove at the downstream of the vent to promote the cavity coalescence was numerically investigated. And the promotion effect of the annular groove on cavity coalescence at different development stages and different working conditions was also studied. The results show that the cavity coalescence is greatly improved by the annular groove. Flow separation in boundary layer occurs when the incoming flow passes through the annular groove in the moving coordinate system because of flow expansion. The induced entrainment of annular groove, on the one hand, retards the axial development of cavity, and promotes the generation of a larger circumferential shear vortex along with expanding in the circumferential direction. On the other hand, part of the ventilation gas is sucked into the annular groove. The gas sucked into the groove is squeezed and broken contributing to the circumferential coalescence. The coalescence cavity in the groove overflows and leaks to promote the upward movement of the cavity coalescence boundary. In addition, under different working conditions, the shape and internal pressure of the cavity become more stable for the groove improving the internal flow state of the cavity.