自振射流频率特性的试验研究

淹没条件下自振射流的频率特性决定着射流的打击效果,而获取射流的压力脉动信号对研究自振射流频率特性至关重要。射流的压力信号通常借助于冲蚀试验和标靶打击试验来间接获得,这里采用喷嘴腔内压力信号提取方法对自振射流频率特性进行试验研究。通过比对分析证明,直接采集腔内压力信号可以有效获取自振射流的频谱特征。与标靶打击试验相比,该方法受随机扰动少,频谱清晰,更有利于自振射流特征频率的提取。在此基础上,通过频谱分析得到自振射流的共振频率,并研究来流参数对自振射流频率特性的影响。试验结果显示,自振射流的共振频率并非是对来流扰动频率的直接放大,且受来流扰动的影响很小。来流速度对自振射流共振频率的影响较大,随着来流速度的增加,自振射流的共振频率及其对应的幅值均显著增加。这表明适当加大来流速度可以有效地改善自振射流的振荡特性。

Experimental Study of Self-resonating Water Jet Frequency Characteristics

The frequency characteristics of self-resonating water jet determine the impact effect of jets under submerged conditions. Obtaining pressure pulsation signals of jets is significant to investigate frequency characteristics of self-resonating water jet. Usually, the pressure pulsation signals are obtained by some indirect method, such as erosion experiments and striking target tests. However, frequency characteristics of self-resonating water jet are analyzed experimentally by directly measuring flow pressure pulsation in a jet nozzle’s cavity. Through comparative analysis, it is proved that the spectrum characteristics of self-resonating water jet can be effectively obtained by collecting pressure signal in the cavity directly. This method has significant advantages over traditional striking target test for less random disturbance and more clear spectrum. Based on this experimental method, resonance frequency of the self-resonating water jet is obtained by spectrum analysis. Furthermore, a series of experiments are carried out to investigate the effects of flow parameters on the spectrum characteristics of jets. The experiment results show that the resonance frequency of the self-resonating water jet is not the direct amplification of disturbance frequency of inflow, and the disturbance frequency of inflow has little effect on jet resonance frequency. However, inflow velocity could greatly affect jet resonance frequency. With the increase of inflow velocity, the resonance frequency of jet and its amplitudes significantly increase. This demonstrates that the increase of inflow velocity can effectively improve the oscillation characteristics of self-resonating water jet.