Numerical investigation of clocking effect on unsteady fluid flow in vicinity of tongue for centrifugal pump with vaned diffuser

In order to investigate the clocking effect on unsteady flow distortion in the vicinity of the tongue and hydraulic loss in the volute, experiments and numerical simulations were conducted with four different relative angular positions between the vane and tongue. Numerical results were validated against experimental data, which included measurements of pressure pulsation at the tongue and downstream of the tongue. The radial and circumferential velocities near the tongue at the diffuser-volute clearance were depicted by expanding the rotating surface, and comparisons were made under different diffuser positions to reveal the flow distortion affected by the clocking effect. Shear stress rates and total pressure distributions at the volute exit pipe were also depicted to study the flow loss in the volute affected by the flow pattern from the tongue. The findings show that the pressure fluctuation at the tongue and downstream of the tongue is significantly affected by the diffuser mounting position. The amplitude and intensity of pressure pulsation under θ d1 are clearly smaller than those at other diffuser positions. As the vane trailing edge approaches the tongue, the pressure gradient becomes very large, leading to the formation of a vortex at the tongue that promotes crowding effects and reverse flow occurring in the exit pipe. This, in turn, leads to deflection of the main flow in the volute, high velocity gradients, and subsequently large shear stress rates and hydraulic losses. When the diffuser is installed at θ d4 , the flow distortion and flow loss are improved.