Experimental and numerical analysis of the unsteady influence of the inlet guide vanes on cavitation performance of an axial pump

The effect of the inlet guide vanes on cavitation performance of an axial pump is investigated to assess the mechanism for cavitation in pumps and improve their cavitation performance. The effect of inlet guide vane angles on cavitation performance was assessed experimentally, and computational fluid dynamics was used to analyze the inner flow field of the axial pump and to probe the cavitation mechanism. The simulation results agree qualitatively with the experimental data, showing that cavitation performance is improved with positive inlet guide vane angles but hampered with negative ones. The cavitation performance itself is controlled by the cavitation volume, which first expands circumferentially when the net positive suction head decreases from a certain large value and then develops toward the axis radially after the net positive suction head reaches a certain value. This is when the cavitation performance deteriorates. Comparing cavitation volume for the critical net positive suction head as determined by two different methods, the method based on efficiency drop (NPSH eff.,1% ) is found to be more suitable than that based on head drop (NPSH head.,3% ). Furthermore, the distribution of swirl is shown to be closely related to the distribution of cavitation, a feature that may be used to predict cavitation along the impeller.