The effects of variable-inlet guide vanes on the performance of an axial flow pump considering tip clearance are investigated. The performance and the main flow field of the whole passage with five different angles of inlet guide vanes ( −10°, −5°, 0°, 5°, 10°) and with two tip clearance sizes (1‰ and 2‰) are presented. The results show that when the angle of inlet guide vane increases from negative values to positive values, the pump head reduces for two tip clearance sizes. This is mainly caused by the change of inlet velocity triangle of blade. Moreover, as tip clearance size increases from 1‰ to 2‰, both the pump head and efficiency decrease because of increasing of the strength of tip clearance leakage vortex and reverse flow.
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 (NPSHeff.,1%) is found to be more suitable than that based on head drop (NPSHhead.,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.
The performances of an axial pump with and without inlet guide vanes (IGVs) are investigated by both experimental method and computational fluid dynamics (CFD) method. Besides the stall inception, an obvious “positive slope” phenomenon appears under off-design operating points in experiment without IGVs. The experimental data also shows that IGVs can change the performance of axial pumps and remove the “positive slope”. The CFD is mainly used to reveal the mechanism of the “positive slope” phenomenon, where the simulated results are firstly validated in comparison with the experimental data. The results obtained show that the reason for this “positive slope” is due to the backflow vortex in front of the impeller, and the tip clearance is found to take an important role in forming this backflow vortex.
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