文氏管非定常空化流动可视化实验研究

Visualization experimental study for venturi tube unsteady cavitating flows

结合高速摄影和脉动压力测量技术,在模拟发动机供应系统动力学边界条件的基础上,开展了某型文氏管非定常空化流动可视化实验研究.获得了空化区详细的内部结构和脉动压力数据,分析了空化区形态的变化和非定常特性.结果表明:随着空化数的降低,文氏管流场从初生空化、膜状空化,过渡至云状空化.在云状空化阶段,文氏管空化流场呈现出复杂的动态过程,空化区可以划分为附着型环向气泡膜和脱落型气泡云.附着型气泡膜作为一个整体,相对较为稳定,内部的压力波动很小.脱落型气泡云上存在大块云团的断裂、脱落和溃灭过程,产生明显的脉动压力峰,脉动压力在频域上表现为无固定频率的宽频带.空化区下游存在局部的高速逆向射流,驱动附着型气泡膜长度不断缩短和伸长,使得气泡膜的长度沿周向也出现明显的不一致.在云状空化阶段,文氏管下游系统出现了290～400 Hz范围的系统性自激振荡.

A visualization experiment of a venturi tube unsteady cavitating flows was conducted, by combining high speed visualization and dynamic pressure measurement technology, on the base of simulating the dynamical boundary conditions of the engine feed system.The detailed interior structure of cavitating flows and the pressure fluctuation data were captured. The variation of cavity shapes and the unsteady characteristics were analyzed. The experiment results indicate that as the cavitation number decreases, the venturi tube cavitating flow is changed from inception cavitation to film cavitation, and to cloud cavitation. At cloud cavitation stage, the venturi tube cavitating flows are revealed as some very complex dynamical processes. The cloud cavitating zone can be divided as attached annular cavity film and detached cavity cloud. The attached cavity film is relatively stable as a whole, and its inner pressure fluctuation is really little. It is found that large part of cavity cloud is breaking and shedding from the total detached cavity cloud, and is going to collapse. These processes induce evident pressure fluctuation pulses, which have wide frequency range but not fixable frequency peak in the frequency region. At the aft end of the cavity cloud, the local high velocity re-entrant flow is discovered, which drives the axial length of attached cavity film shortening and extending, and induces the film length obviously unequal along the circle. The self-oscillation of 290–400 Hz also takes place at the downstream system of venturi tube, at the cloud cavitation stage.