基于非线性水声模型的离心泵空化喘振研究

Cavitating surge will cause severe pump vibration and system oscillation, which is very harmful to the safety of the pipe system and pumps. It is known to be an auto-oscillation cavitation phenomenon related with both pump cavitation and system characteristics. The project propose to use state equation method to establish an 1D (one dimensional) nonlinear hydro-acoustic model which is suitable for the stability analysis complex pipe system including cavitating pump and write the related program. Then the coupling method of one dimensional hydro-acoustic analysis and 3D (three dimmensional) cavitating flow simulation will be studied. Through the combination analysis of 3D cavitating flow simulation and the pump cavitation experiments, the project will focus on the following issues: (1) the quasi-state relation between the cavitation compliance \ mass flow gain factor with pump head and discharge、the Thomas number and the specific speed of centrifugal pumps. (2) The Dynamic character of the cavitation compliance \ mass flow gain factor, that is, the phase delays and their relations with the oscillation frequency as well as the nonlinear character of the thermodynamic damping of phase change. (3) the three dimensional character and back flow character and their influence on the cavitating surge phenomena in centrifugal pumps. The purpose of the study is to provide a useful tool for the stability analysis of the pumping system with cavitation, to clarify the main reason of system fluctuation related with cavitation, to identify the main factors that may influence the frequency\amplitude of the system response and give suggestion to the pump design and pumping system design and operation.

空化喘振会引起泵自身的振动和系统参数的波动，对泵及系统的安全运行非常不利。空化喘振是与泵自身空化特性及管路系统同时相关的自激振荡，为此，本项目拟以离心泵系统为研究对象，采用状态方程的方法建立适用于复杂管路的非线性水声模型并编制用于含空化水力系统稳定性分析的计算程序,研究非线性水声模型与泵的三维非定常流动计算的耦合算法，结合泵的三维空化流计算结果及离心泵的空化试验结果，主要针对以下问题展开研究：（1）离心泵的空化柔度和流量增益与泵比转速、运行工况、空化系数等参数的准静态关系；（2）空化柔度和流量增益及其相位延迟与振荡频率的关系等动态特性、相变的非线性耗散效应及其对的空化喘振特性的影响；（3）发生空化喘振时泵内的三维空化流动特征和回流特征及其对系统稳定性的影响，以期更加全面地揭示泵空化不稳定现象发生的原因和影响因素，为水力系统工程设计、故障诊断及安全稳定运行提供指导。

空化喘振会引起泵自身的振动和系统参数的波动，对泵及系统的安全运行非常不利。空化喘振是与泵自身空化特性及管路系统相关的自激振荡，本项目以离心泵系统为研究对象，采用等效电路法建立了含空化的水力系统振荡理论模型，分析了泵空化喘振的原因并给出了发生喘振的临界条件，可简单用流量增益系数是否大于空化柔性与流阻之积来判断喘振发生条件；通过三维空化流动计算，获得了不同比转速离心泵的空化声学参数与运行工况的准静态关系及动态变化特征，结果表明低比转速的静态空化流量增益系数在大部分工况范围内都是负值，而高比转速离心泵在一些小流量工况范围内由于回流的影响会出现静态空化流量增益系数为正的情况，在有流量和压力波动的条件下空化声学参数会出现相应的非线性变化；在此基础上建立了含空化的水力系统非线性水声模型并完成了软件编制，可用于预测空化喘振及含空化的水力系统瞬变过程。对空化喘振工况的分析结果表明，空化喘振频率随管长的增加而减小，随空化系数的减小而减小；研究了一维非线性水声模型与三维空化流动模型的耦合计算方法，通过商用软件及自定义函数实现了两个模型耦合计算，获得了回流的响应特征，即高于该固有振荡频率的激励对回流空化引起的振荡频率无明显影响。而激励频率低于回流喘振频率时系统表现处受迫振荡特点，振荡频率为激励频率。