In order to explore influence of interstage seal clearance on the performance and flow field of multistage well pumps, a newtype well pump QS-40-30-55 was taken as the investigation model; the whole flow field in the pump with different seal clearances were stimulated with Fluent. Effects of the clearance on the overall performance and internal fluid flow field in the pump were analyzed. The results showed that the head and efficiency of the pumps are reduced, while the shaftpower remains unchanged with increasing clearance at the same flow rate. A stream of liquid in the guide vane exit flows back into the impeller hub along the interstage seal clearance and then it moves into the guide vane through the side chamber between the impeller and the guide vane, causing a disturbance in the flow at the guide vane exit and the entrance to the next stage impeller, which increases the hydraulic losses and degrade the pump performance. The experimental results of the prototype of the pump show the best efficiency point occurs at a lower flow rate than the specified one, but it is still in accord with the National Pump Test Standard of China. Because the impeller disc friction loss and the leakage loss through the interstage seal clearance have been involved in the computational model, the estimated performance by CFD is in very good agreement with experiments (error is less than 1％), confirming the validity of CFD numerical simulation approach. Those results might be instructive for optimal design of newtype well pumps, especially whose impellers are designed by means of the impeller diameter maximization method.
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