Frequency spectrum analysis for hump characteristic in a pump turbine

In order to analyze the instabilities during the hump region, three dimensional unsteady incompressible simulations are carried out using SST k-ω turbulence model for a scaled model pump turbine at the 18 mm guide vanes opening in pump mode. And 12 monitoring points are set on the whole pump turbine model passage. Then, pressure fluctuation for different operation conditions is analyzed compared with the best efficiency point. Finally this research states the cause of dominant frequency and the principle of spectrum varying with discharge. The results show that blade passing frequency occurs mainly at the best efficiency point, and for all the monitoring points excluding guide vane inlet point, the value of 0.25-1 time rotation frequency feathers obviously higher than the blade passing frequency one with discharge declining, especially in the hump region.