Turbulence modelling for RANS CFD analyses of multi-nozzle annular jet pump swirling flows

摘要

This study focusses on the fluid mechanic analysis and performance assessment of a one-phase swirling flow multi-nozzle annular jet pump using Reynolds-averaged Navier-Stokes simulations and experimental measurements carried out with a bespoke test rig. The numerical investigation of the flow physics of the device, key to understanding its fluid dynamics and optimising its performance, is made particularly challenging by the existence of flow swirl. Thus, the predictive capabilities of two alternative approaches for the turbulence closure of the Reynolds-averaged Navier-Stokes equations, namely the k - omega shear stress transport and the Reynolds stress models, are assessed against measured static pressure fields for three regimes characterised by different swirl strength, and a thorough cross-comparative analysis of the flow physics using the two closures is performed to complement the information provided by the experimental measurements. At the lowest swirl level, the two simulation types are in very good agreement, and they both agree very well with the measured static pressure fields. As the flow swirl increases, the two numerical results differ more and the Reynolds stress model is in better agreement with the measured static pressure. At the highest swirl level the shear stress transport analysis predicts weaker dissipation of the jet energy and stronger mixing of injected and pumped streams, resulting in higher performance predictions than obtained with the Reynolds stress model. A CFD-based sensitivity analysis also highlights the impact of nozzle diameter and flow swirl on the pump performance, proving new guidelines for the design optimisation of this pump.