Numerical Analysis of the Effect of an Idler Disk on Centrifugal Pump Performance

Designing a centrifugal pump impeller comes with challenges due to multiple parameters that affect the pump efficiency. A high velocity gradient exists in the flow between the impeller shroud and sidewall of the pump casing due to one surface stationary and the other moving at a high velocity. The internal rotating flow in the impeller shroud-sidewall gap is a major problem that leads to a decrease in pump performance. This study presents a design modification of the gap between the impeller shroud and the pump casing sidewall using an idler disk located in between, which rotates freely during pump operation. In this paper, a numerical analysis was performed to investigate the idler disk's effect on the pump performance for different volumetric flow rate values and idler disk geometries. ANSYS-2019-R1 was used (FLUENT solver) to carry out the computational fluid dynamics (CFD) analysis for evaluating the performance of the baseline and modified designs in a centrifugal pump. The flow field between the impeller shroud and sidewall of pump casing was investigated using 3-D Naiver-Stokes equations with a Realizable k-є turbulence model. Standard water was used as the working fluid, and the simulation was conducted at a fixed angular velocity of the pump impeller. The flow pattern, velocity distribution, pressure distribution, shear stress, and velocity gradient in the impeller shroud-sidewall gap are presented in this study. The numerical analysis provided an idea of how the freely rotating disk behaved during pump operation. A comparative study was conducted between the flow field's simulation results for the existing impeller model (without idler disk) and modified designs (with different idler disks). The best performing case of centrifugal pump operation with an idler disk was identified.