Hub shape effects on the inducers performance under cavitation

Abstract

In this work, experimental and three-dimensional numerical simulations are pursued with the intent of elucidating the differences that the hub shape has on three inducer performances and on other important engineering properties in cavitating and non-cavitating regimes. Two inducers have a cylindrical hub and the third one has a conical hub. They are noted as BH inducer (big hub), SH inducer (small hub), and CH inducer (conical hub). These machines were designed with the goal to reduce the amount of cavitation and vibration, on the one hand, and to improve the overall performance, on the other hand. Both sets of experimental and numerical data suggest that the cavitating and non-cavitating performances are affected by changes in the hub shape. The hub configuration and cavitation numbers considered give rise to various cavitation structures on the suction side of the blades, characterized — at some flow rates — by recirculating flow regions and backflow vortices. The results show the relative superiority of the CH inducer through the critical cavitation coefficient of 5 per cent, even if this inducer is very unstable for all flow rates. It was also found that the BH inducer is the most stable and that for a 15 per cent head drop, the three inducers have quite the same performances.

The main experimental and numerical results presented here concern the overall performances, especially the hydrodynamic mechanism of head drop and the visualization of three-dimensional flow structures. We also present the vibratory behaviour versus the flow rate and the suction pressure. The computational three-dimensional flow in non-cavitating regimes enabled us to explain the unstable and cavitating operation for off-design conditions. The numerical computation in cavitating flows is carried out using the computational fluid dynamics (CFD) software CFX-TASCFlow^2.12, which cavitation model was validated on our BH inducer.