水轮机空化状态声发射信号的小波包能量特征

为了充分提取水轮机空化状态下声发射信号蕴含的时频特征及其变化规律，基于混流式水轮机模型空化试验，采集了间隙空化不同阶段时典型测点的声发射信号，采用小波包分析方法提取了声发射信号的小波包能量等特征参数，分析了这些参数随水轮机空化系数变化的关系。结果表明，随着水轮机空化系数的逐渐减小，从无空化、空化初生到完全空化状态，在导叶拐臂和转轮下环底部采集到的声发射信号的小波包能量随之发生了明显的规律性变化。开始时小幅缓慢增加，在空化初生附近达到某一峰值，接着略有回落，然后在临界空化状态时急剧增加达到较之以前更大的峰值，最后急剧回落。

Wavelet packet energy features of acoustic emission signals from hydraulic turbines under cavitation

To fully study the time and frequency characteristics of acoustic emission (AE) from hydraulic turbines in cavitation conditions, this paper conducts a series of cavitation tests on a model Francis turbine, collects AE signals and extracts their features in the form of wavelet packet energies in frequency bands, and analyzes their variation relations in different cavitation stages. The results show that with cavitation coefficient decreasing gradually, the operation condition of the turbine changes from no cavitation to incipient cavitation, then to fully developed cavitation stage. Accordingly, significant variations occur in each of the wavelet packet energies in the feature frequency bands of AE signals collected from the locations of the guide vane lever and the runner lower band. In this process, the energy increases quite slowly at initial stage, reaches a peak around incipient cavitation and decreases slightly, then increases violently at critical cavitation until a peak value much greater than the first one, and finally drops sharply.