气液两相条件下离心泵内部流动特性数值计算和试验研究

发布时间：2018-07-25 18:00

【摘要】：泵在气液两相流条件下运行的现象经常会出现在工程实际中,而工作介质中的气体的存在对离心泵性能影响比较明显,气液两相流条件下离心泵运行特性会发生较大的改变,且会产生剧烈的振动现象,严重时发生喘振从而影响系统的可靠运行。因此,开展气液两相流条件下离心泵内部流动机理及流动诱导特性研究具有重大的理论意义和工程应用价值。本文通过试验测试和数值计算相结合,基于已有的研究基础和流动理论分析开展研究,进行了不同转速不同含气率下模型泵的外特性试验以及压力脉动、振动等动态性能试验,并且基于欧拉非均相流模型对模型泵在气液两相流动状态下的内部流场进行定常和非定常数值计算,主要研究内容及成果如下:1.从基础理论研究、试验研究以及数值研究三方面分析了国内外泵内气液两相流动的研究现状,并进行总结提出了不足,阐述了进行气液两相条件时泵内部流动特性研究的意义。2.搭建了离心泵气液两相测试试验台,进行了不同转速、不同含气率条件下的外特性试验,得出如下结论:气液两相条件时,在小流量工况时(φ㩳0.04),进口含气率超过1%性能就会急剧下降,而且运行工况范围会随着进口含气率增大逐渐减小;在进口含气率低于8%时,理论扬程与所输送流体介质密度无关;进口含气率低于3%时发现转速相似定律依然能够成立。3.采用LMS测试系统,在不同进口含气率条件下对模型泵进行动态性能试验,获得了不同运行工况条件下出口压力脉动及振动频谱特性,得出如下结论:压力信号和振动信号均服从正态分布;当进口含气率超过5%时,发现低频区压力脉动幅值明显增大;振动信号的整体幅值会随着含气率的增大明显增大,尤其是在低频段区域,随着含气率逐渐增大,振动呈先减小后增大再减小的趋势,在进口含气率5%时振动最大,进口含气率超过5%后,低频区振动能量也会成为泵系统振动能量重要组成部分。4.基于欧拉非均相流模型,在不同流量、不同进口含气率工况下对模型泵进行定常和非定常数值计算,得出如下结论:在进口含气率超过3%后,初始气泡直径是计算时需要考虑的重要因素;随着含气率的增大,气体有沿着吸力面向出口边运动的趋势,气体可以一定程度上改善叶轮进口回流现象,气体在叶轮内的聚集与漩涡的产生有关;进口含气率达到3%时,低频区幅值会出现小幅的增大,产生宽频脉动,而且低频区宽频脉动的范围会随着含气率的增大而变宽,含气率越高对低频宽频脉动的影响越明显。
[Abstract]:The phenomenon of pump running under the condition of gas-liquid two-phase flow often appears in engineering practice, but the existence of gas in working medium has obvious influence on the performance of centrifugal pump, and the operation characteristics of centrifugal pump will be changed greatly under the condition of gas-liquid two-phase flow. Violent vibration will occur and surge will occur in severe cases, which will affect the reliable operation of the system. Therefore, it is of great theoretical significance and engineering application value to study the flow mechanism and flow induction characteristics of centrifugal pump under the condition of gas-liquid two-phase flow. In this paper, through the combination of test and numerical calculation, based on the existing research foundation and flow theory analysis, the external characteristic test of the model pump with different rotational speed and different gas content, the dynamic performance test of pressure pulsation and vibration are carried out. Based on the Eulerian heterogeneous flow model, the steady and unsteady numerical calculation of the internal flow field of the model pump in the gas-liquid two-phase flow state is carried out. The main research contents and results are as follows: 1. The present research situation of gas-liquid two-phase flow in pumps at home and abroad is analyzed from three aspects: basic theoretical research, experimental study and numerical study, and the deficiencies are summarized and put forward. The significance of the study on the flow characteristics of pumps under gas-liquid two-phase conditions is expounded. In this paper, the gas-liquid two-phase test rig of centrifugal pump is built, and the external characteristic test under different rotating speed and different gas content is carried out. The conclusion is as follows: when gas-liquid two-phase condition, When the flow rate is small (蠁 0.04), the performance of the inlet gas content will decrease sharply when the inlet gas content exceeds 1%, and the operating condition range will gradually decrease with the increase of the inlet gas content, and when the inlet gas content is lower than 8, the theoretical head will have nothing to do with the density of the fluid. When the imported gas content is lower than 3, it is found that the law of speed similarity still holds. 3. The dynamic performance of the model pump was tested with LMS test system under different inlet gas content. The characteristics of outlet pressure pulsation and vibration spectrum were obtained under different operating conditions. The conclusions are as follows: the pressure signal and vibration signal are obeyed to normal distribution; when the inlet gas content exceeds 5, it is found that the amplitude of pressure pulsation increases obviously in low frequency region, and the whole amplitude of vibration signal increases obviously with the increase of gas content. Especially in the low frequency region, with the increase of gas content, the vibration decreases first, then increases, and then decreases. When the inlet gas content is 5, the vibration is maximum, and the inlet gas content is more than 5%. Low frequency vibration energy will also become an important component of pump system vibration energy. Based on the Eulerian heterogeneous flow model, the steady and unsteady numerical calculation of the model pump is carried out under different flow rate and different inlet gas content. The conclusion is as follows: when the inlet gas content exceeds 3%, The initial bubble diameter is an important factor to be considered in the calculation. With the increase of the gas content, the gas tends to move along the suction side towards the outlet, and the gas can improve the inlet reflux phenomenon of the impeller to a certain extent. The accumulation of gas in the impeller is related to the formation of swirl. When the inlet gas content reaches 3, the amplitude of the low frequency region will increase slightly, resulting in a wide band pulsation, and the range of the wide frequency fluctuation in the low frequency region will become wider with the increase of the gas content. The higher the gas content is, the more obvious is the influence on the low frequency broadband pulsation.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH311

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