绕回转体初生空化流场特性的实验及数值研究

EXPERIMENTAL STUDY ON FLUCTUATING HYDRODYNAMICS AROUND AXISYMMETRIC BODIES

该文采用实验与数值模型相结合的方法对绕回转体的初生空化流场进行了分析,研究了头型对初生空化流场特性的影响,数值模型中,为了精确捕捉由于分离流动而产生的漩涡结构,湍流模型采用了一种基于空间尺度修正的滤波器模型(FBM),实验中,采用高速录像技术观察了初生空化形态,并应用粒子测速系统(PIV)测量了相应工况下,初生空化流场的速度及涡量分布,研究结果表明:头型对绕回转体的初生空化流场具有显著的影响,不同回转体的初生空化数随着肩部曲率突变增大而逐渐增大,在初生空化工况下,平头和锥头回转体肩部的高剪切流动区出现了不规则的漩涡分离结构,初生空化首先在该分离区域内产生,而不是发生在回转体的物面上或在物体邻近处,此时,初生空化流场体现出明显的漩涡脉动特性,流场中的低速高脉动区域对应于空化核心区,涡量主要亦集中在该漩涡分离区域内,对于圆头回转体,其初生空化流场比较稳定,"指状"的片状空泡附着在回转体表面上。

Inception cavitating flows around axisymmetric bodies with different headforms, including the blunt, conical, and hemispherical objects are studied, based on experiments and numerical simulations. In order to accurately capture the vortex separation structure, a filter-based turbulence model （FBM） is used in numerical simulations. Meanwhile, a high-speed video camera and Particle Image Velocimetry （PIV） are used to visualize the inception cavitating flow structures, and to measure the velocity and vorticity fields. Both experimental and numerical results show that the headforms have significant impact on the inception cavitation flows. For the axisymmetric bodies with blunt and conical headforms, the inception cavitation number is much larger than that of the hemispherical one. In the inception cavitation condition, for the blunt and conical bodies, the high shear vortex structures locate in the shoulder area, and the inception cavity appears in the boundary layer separation zone near the wall instead of the adherent area. Here, the inception cavitation flow field reflects the vortex characteristics, while the high-fluctuating region and lower velocity area relates to the cavitation area. But for the hemispherical, the inception cavitation flow is very stable, and the sheet cavity attaches to the wall surface.