Towards the pumped-hydro energy storage: Improvement on the flow instability and cavitation performance with application-oriented forward skew angle of impeller blades

Although the turbulent-cavitating flow usually induces great hydraulic losses and excessive pressure fluctuations, little guidance on the impeller modification methods to improve pump performance has been universally proposed. In present research, enormous numerical simulations and experiment measurements are carried out to discuss hydrodynamic characteristics in pumps configured with different skew angle of impeller blades. Results reveal that as the skew angle increases, the hump region is postponed to the lower part-load condition with a lower head drop, which decreases from 0.0514 for model A to 0.0242 for model E. Furthermore, it is found that the rotating stall evolution in the impeller flow passage would induce great energy transfer. For the model A, the pressure loss increment (29.6 %) in the impeller flow passage is higher than that in the diffuser (8.0 %). Additionally, as large skew angle blades are adopted, the rotating stall is transferred to the synchronous stall cell and the cavitation performance is also improved. The critical cavitation number is decreased from 0.186 to 0.165 by calculation under the best efficiency point condition as the skew angle of 28° is adopted. These findings provide feasible guidance for impeller design and optimization on the pump performance improvement.