RESEARCH ON UNSTEADY PRESSURE FIELD WITHIN A HYDRAULIC TURBINE VOLUTE

The unsteady pressure pulsation of an internal flow field within a hydraulic turbine is one of the major factors affecting the stability of a turbine unit. Computational Fluid Dynamics software was adopted in the steady and unsteady flow filed analyses. Time and frequency domain analyses were performed on the data acquired at different circumferential positions, radial positions and flow rates. Results show the number of pressure pulsation within one impeller rotational cycle equals a blade number. The amplitude of pressure pulsation at the volute inlet pipe and cut water is minor, however it is intensive at the middle of a volute spiral part and before the cut water. The main frequency and secondary main frequency of pressure pulsation within a volute are blade frequency and two times of blade frequency. Investigation into pressure pulsation at different flow rates shows that the amplitude of pressure pulsations increases with flow rates. To verify the numerical result, the investigated hydraulic turbine was manufactured and an open hydraulic turbine test ring was built. The performance and unsteady pressure pulsations of the hydraulic turbine were acquired through experimental research. The validity of numerical simulation is confirmed through the comparison between experimental and numerical results.