Study on the chaotic dynamic characteristics of pressure fluctuations in hydro-turbine

Abstract:

To effectively conduct the operating monitoring and malfunction detection of hydro-turbine, this paper investigated the pressure fluctuation characteristics of hydro-turbine running at partial flow conditions, by using the chaos dynamics. Quantitative information of experimental data was obtained. For the pressure fluctuation data monitoring at draft tube, the lifting wavelet transform was adopted to perform the de-noising, hereby, the fluctuation signal distribution on the frequency domain, the energy changing, and the energy partition accounting for the total energy was calculated. Then, for the flow conditions ranging from no cavitation to severe cavitation, the chaos dynamic features of fluctuation signals were analyzed, including the temporal-frequency distribution, phase trajectory, Lyapunov exponent and Poincaré etc.. It is revealed that, the main energy of pressure fluctuations in the draft tube locates at low-frequency region. As the cavitation grows, the amplitude of power spectrum at frequency domain becomes larger. For all the flow conditions, all the maximum Lyapunov exponents are larger than zero, and they increase as well. Therefore, it is believed that there indeed exist the chaotic attractors in the pressure fluctuation signals. Based on the multi-condition analysis, the on-line operating monitoring can be accomplished.