Due to the S-shape characteristics and the complicated flow in pump turbine, there may be serious instability when the pump-storage power plant starts. In order to conduct further study on the energy dissipation in hydraulic turbine, three dimensional incompressible steady state simulations were applied using SST k-ω turbulence model in this paper. It can be seen that the simulation results are consistent with experimental results well by the comparison of characteristic curves, and further analyses were made based on the entropy production theory. It is shown that the entropy production of spiral casing accounts for the minimum proportion in all components. The entropy production of cascades and runner differs a lot at different guide vane openings, and it features "S" characteristics with the increase of discharge. Then, the analysis of entropy production distribution on runner, blade cascades and draft tube was carried out at the 10mm guide vane opening. It was found that the losses in guide vane space is much higher than that of stay vane space and the losses are mainly in the tail area of stay vanes and vaneless space. The losses mainly occurs in the leading edges and the trailing edges of blades. The largest losses mainly lie at the wall of straight cone near the inlet in draft tube. The losses at the inner surface of elbow are also very high. The results indicate that the method based on the entropy production theory is very helpful to analyze and locate the losses in hydraulic turbine.

This paper presents a technique for front image sensing of the weld pool in variable polarity plasma arc welding of aluminum alloys, and describes the determination of the geometrical size of the keyhole for subsequent real-time feedback control of a full penetration weld. Image formation occurs when the arc light reflects off the concave mirror-like surface of the depressed keyhole weld pool, and passes through a band-pass filter onto the image sensor. The image of the visual keyhole (nominal keyhole) is a two-dimensional projected picture of the actual keyhole weld pool. The variation in area of the nominal keyhole is closely correlated with the variation of the bottom width of the weld bead.

During the process of switching conditions in pump-turbine, unstable flow would take place and seriously impact on the stability and safety. This paper deals with the guide vanes' moving process in pump mode through unsteady numerical simulations. Dynamic mesh methodology is used for simulations in which GVO (Guide Vane Opening) from 9mm to 26mm. Simulation results approve that, there are many complex vortex structures and flow blockages phenomena under small GVO condition. Through the mathematical method of Fast Fourier Transform (FFT) and Short-Time Fourier Transform (STFT), the dominant pressure fluctuation frequencies are from runner blade passing frequency (BPF) and its harmonic frequency, as well as some other low frequencies are from unsteady flow states. Furthermore, the flow states are more unstable and complex under small guide vanes moving process. Compared with fixed GVO position, the flow states are more unstable and complex under guide vanes moving process, while the amplitude of main frequencies becomes higher.

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