Numerical simulations on impeller-diffuser interactions in radial diffuser pumps are conducted to investigate the unsteady flow, and more attention is paid to pressure fluctuations on the blade and vane surfaces. Calculations are performed at different operating points, different blade number configurations, and different radial gaps between the impeller and diffuser to examine their effects on the unsteady flow. Computational results show that a jet-wake flow structure is observed at the impeller outlet. The biggest pressure fluctuation on the blade is found to occur at the impeller trailing edge, on the pressure side near the impeller trailing edge, and at the diffuser vane leading edge, independent of the flow rate, radial gap, and blade number configuration. All of the flow rate, blade number configuration, and radial gap influence significantly the pressure fluctuation and associated unsteady effects in the diffuser pumps.
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