【作者】 王健；

【导师】 李江云；

【作者基本信息】 武汉大学 ， 市政工程， 2013， 博士

【摘要】 本文针对用于水射流清洗工业的自激脉冲射流装置的打击力与打击频率展开研究,采用数值仿真、流体网络以及模型试验等方法从微观到宏观,对不同的自激脉冲发生机理进行解释,获得了脉冲射流频率及振幅随结构参数和工作参数变化的规律。在总结自激脉冲射流发生机理的相关理论中,针对高压小流量的波-涡作用机理及低压大流量的空气弹簧机理,基于不同的工作条件对其进行解释和统一,提出在高压小流量的装置形式下,由于流速过快,流体在腔内的停止时间小于空化发生的豫驰时间,故自激脉冲现象由波涡扰动产生；而在低压大流量的装置形式下,空化气囊得到充分发展,气囊的周期性夹缩是产生脉冲射流的主因。为完善自激脉冲射流装置的数值计算方法,提高模型的预测能力,优化参数范围,基于三维非定常空化模型,对自激脉冲射流装置的结构参数和运行参数进行分析,发现不同参数配比对自激脉冲频率的影响较大,当d2/d1=1.8时,嘴间距Lc为36mm时,自激频率最低,振幅最大,自激效果最为明显。工作压力达到2MPa及以上时,方能产生有效的自激现象,随着压力增加,自激频率减小,振幅增大,且二者的变化趋势渐趋平缓,1～4MPa是压力调制的有效范围。自激喷嘴结构不同导致不同的自激振荡波形；在同一喷嘴结构参数下,改变工作压力将改变自激频率及峰值带宽,但自激脉冲的波形相近。在结构参数一定的情况下,自激频率与入口流速呈幂函数关系。工作压力相同的情况下,斯特劳哈尔数随结构参数的变化不明显。利用改进后的模型进行计算发现,改进后模型对于自激效果参数的模拟精度有所提高,对出口流速峰值持续时间的模拟精度有所提高。利用流体网络理论的相关原理研究系统外特性对自激主频和振幅的影响,建立了自激振荡腔的频率响应函数,通过程序计算发现,自激振荡腔具有低通滤波的特性,存在一个和结构参数和运行参数相对应的主频率,当来流脉动频率在主频率附近时,可在自振腔的选择性放大下发生共振,形成脉冲射流。系统主频对应的幅值越高,相应的主频率越小,通频带越窄。对于双腔室自激振荡腔而言,两阶段放大的设计使得扰动波振幅明显增大,但由于扰动反馈路径的延长,其频率较小,沿程水头损失较大。为了验证理论分析结果,建立了一套完整的动力输送、自激发生、数据采集系统。通过模型试验和数值计算的自激频率的对比发现,采用本文数值建模方法对自激脉冲频率进行预测足可行的，由于出口射流主要以汽水混合的形式射出,同体积流体的质量较连续射流低，因此虽能够明显提升流速,却无法等倍提高打击力,根据模型试验结果,在下喷嘴直径和工作压力相同的情况下,脉冲射流的打击力可以达到连续射流的1.3-2倍左右,满足最大打击力振幅的最优结构参数为：d1=5.9mm, d2=10.7mm, Dc=72mm, Lc=36.6mm, P=2.9MPa,相应配套关系可作为中低压条件下自激脉冲喷嘴设计的依据。更多还原

【Abstract】 Directing at the hitting force and hitting frequency of the self-excited pulsing jet device used in the industry of water jet cleaning,methods such as numerical simulation, fluid network theory and model test are used from the micro to the macro.The various kinds of occurrence mechanisms are explained,the law of the pulsing jet frequency and amplitude depending on the structure and working parameters is obtained. Based on different working conditions,the mechanism of wave-vortex under high pressure-small flow and mechanism of air spring under low pressrue-large flow are explained and united through the summary of the related theory of occurrence mechanism of self-excited pulse flow.Because of the high flow rate under the high pressure-small flow, the stagnation time of the fluid in the cavity is less than the relaxation time of cavitation,so the self-excited pulse is caused by the wave-vortex perturbation;while under the low pressrue-large flow,the cavitation gasbag is fully developed and the periodic shrink of the gasbag is the major cause of pulse jet.In order to improve the numerical computation method of self-excited pulsing jet device,increase the predictive ability of the model and optimize the range of parameters,based on the3D unsteady cavitation model,structure and working parameters of the self-excited pulsing jet device which have a significant impact on the frequency of the self-excited pulse are analysed.The best self-excited effect with minimum frequency and maximum amplitude is produced when d2/d1=1.8, Lc=36mm. The effective self-excited phenomenon is produced when the working pressure equal or greater than2MPa.The frequency decreases and the ampitude increases with working pressure increasing,but the variation trend slows down, the effective range of the pressure modulation is1～4MPa.Different structures of the self-excited nozzle have different pulse wave form;under the same structure,the change of the working pressure can change the self-excited frequency and peak bandwidth but not the wave form.The relationship between the self-excited frequency and inlet velocity is a power function under the same structure.The Strouhal numbers under same working pressure and different structure parameters nearly the same.The improved cavitation model has higher simulation accuracy which leads to more realistic time of duration of the peak of the outlet flow velocity.The frequency response function of the self-excited pulse cavity has been founded based on the correlation theory of fluid network theory so as to study the influence of external characteristic of the system. Calculated by the program,the self-excited pulse cavity has the character of lowpass filter,the main frequency related to the structure and working parameters exists and the resonance leading to pulse jet can be produced by the selective amplification of the cavity when the frequency of the incoming flow pulsation approximately equal to main frequency.The higher of the amplitude,the lower of the relevant main frequency and the shorter of the transmission bands.For double-cavity self-excited pulse nozzle,thc amplitude of disturbance wave significantly increases by the design of two-stage amplification,but the frequency decreases and the frictional head loss increases with the elongation of the path of disturbance feedback.The test bed of self-excited pulsing jet device has been founded to prove the results of theoretical analysis and a whole system consist of dynamical transporl,self-excited produce and data collection has been formed. The contrast between the numerical simulation and the model model test shows that the forecast of the self-excited pulsing frequency is feasible using the modeling approach proposed in chapter3.Because of the steam-water mixture form of the outlet flow,the density of the pulsing jet is less than that of the continuous jet which leads to the result that the hitting forcce can not be increased in proportion to the outlet velocity.According to the results of the model test,the hitting force of the pulse jet can be1.3～2times of that of the continuous jet.The best structure parameters with the biggest hitting force amplitude are: d1=5.9mm, d2=10.7mm, Dc=72mm, Lc=36.6mm, P=2.9MPa.The corresponding relationship can be the foundation of the design of self-excited pulse nozzle under mesolow.更多还原