赫姆霍兹喷嘴自振射流特性的试验研究

Experimental study on characteristics of self-resonating water jet for Helmholtz nozzle

为了提高低透气性煤层的采前预抽效果,增加赫姆霍兹喷嘴自振射流冲蚀效率,基于信号分析方法,从射流的流动状态入手研究赫姆霍兹射流的本质特性。采用传感技术直接获取喷嘴腔内流体压力脉动信号,基于频谱分析法研究不同结构的赫姆霍兹喷嘴产生的自振射流的振荡特性。然后采用声传技术检测围压下自振射流打击标靶时的噪声等级,通过声功率谱探讨了自振射流的空化效果。试验结果表明:赫姆霍兹喷嘴上部分结构参数对自振射流的频谱结构和自激共振频率大小起决定作用,而下部分振荡腔结构对自振射流的频谱幅值具有选择性放大功能,但对自振射流的频谱结构几乎无影响;赫姆霍兹喷嘴上部分结构促进了自振射流的空化产生,而下部分振荡腔增强了自振射流的空化效果。射流的幅频特性和声功率谱研究可为自振射流喷嘴的设计提供新途径。

In order to improve the pre-extraction effect of low permeability coal seam,increase the erosion efficiency of self-resonating water jet for Helmholtz nozzle.The oscillating characteristics of self-resonating water jet generated by a series of Helmholtz nozzle in different structures was analyzed base on spectrum analysis method. The noise level when self-resonating water jet hits the target was detected using sound transmission technology and the cavitation effect of self-resonating water jet was discussed through analysis of noise power spectrum.The experimental results showed that comparing to the other nozzle,self-resonating water jet produced by Helmholtz nozzle has the best oscillating characteristic and cavitation effect; the spectrum structure of self-resonating water jet and the size of the self-resonating frequency are determined by the structure parameters of the upper portion of Helmholtz nozzle. While the oscillation cavity in the lower portion has selective function of amplification on spectrum amplitude of self-resonating water jet,yet it almost has no effect on the spectrum structure of self-resonating water jet. The cavitation generation is promoted by the upper portion of Helmholtz nozzle,while the cavitation effect is enhanced by the oscillation cavity in the lower portion. Research of the amplitude-frequency characteristics and noise power spectrum of the jet provides novel method for the design of self-resonating water jet nozzle.