混流式水轮机空化声发射信号的混沌特性分析

Chaos Analysis on Acoustic Emission Signals of Francis Turbine Under Cavitation

针对水轮机空化过程中声发射信号表现出的强烈非线性和非平稳性,提出了水轮机空化声发射信号的混沌特性分析方法,研究了混流式水轮机空化声发射信号的混沌特征及其变化规律。基于混流式水轮机模型空化试验采集了不同空化状态下典型测点处的声发射信号,检验其混沌性后进行相空间重构,计算得到重构信号的关联维数和最大Lyapunov指数,分析了这2种混沌特征参数随水轮机空化状态变化的规律,明确了水轮机空化声发射信号的混沌特征参数与空化状态之间的对应关系。结果表明:关联维数和最大Lyapunov指数不仅可以定性地表征空化状态,而且可以定量地描述空化程度;这2种混沌特征参数受单位转速的影响比受导叶开度的影响更大。

In view of the strong nonlinearity and nonstationarity of acoustic emission signal from hydraulic turbine under cavitation,a chaotic analysis method of acoustic emission signals was established,and the chaotic characteristics and the change law of acoustic emission signals from Francis turbine under cavitation were studied.A series of cavitation tests on a model Francis turbine were conducted,and the acoustic emission signals of typical measuring points under different cavitation conditions were collected.The correlation dimension(DC)and the Largest Lyapunov Exponent(LLE)of the reconstructed signal were calculated.Variation laws of these two chaotic characteristic parameters under cavitation state of hydraulic turbine were analyzed,and the corresponding relationship between the chaotic characteristic parameters of hydraulic turbine cavitation acoustic emission signal and the cavitation state was clarified.Results show that DC and LLE can describe the cavitation state qualitatively and the cavitation degree quantitatively.Also,the influence of unit speed on two chaotic characteristics is greater than that of guide vane open degree.