Large Eddy Simulation of Unsteady Turbulent Flow and Pressure Fluctuation in an Axial-Flow Pump with Various SGS Models

Abstract

Three dimensional Large Eddy Simulation (LES) is performed to predict the unsteady turbulent flow and pressure fluctuation in an axial-flow pump with two different Subgrid-Scale (SGS) models. The specific speed of the axial-flow pump is 518. The calculated flow rates are Q/Q d =0.7, 0.8, 0.9 and 1.0, where Q d is the flow design point. Both the classical Smagorinsky-Lily SGS model [1] and the dynamic Smagorinsky-Lily SGS model [2] are used as the turbulent eddy viscosity model of LES with finite volume method and slide-mesh methodology, and the constant Cs in the later model is dynamically computed based on the information provided by the resolved scales of motion. The computational domain includes the rotator, the fixed guide-vane and the diffuser of the axial-flow pump (See Figure 1). The total head, shaft power and efficiency of the pump are obtained by the simulation and compared with the experimental measurements. The prediction results of the two SGS models are also compared. Both the SGS models successfully resolve the turbulent flow in the pump, and have good agreements with the experimental data. The pressure fluctuation of the flow in pump is predicted too, and the results show that the pressure fluctuation may be the leading role in unsteady hydraulic force generation. The simulation indicates that the numerical method presented in this paper has its potential capability to predict 3D unsteady turbulent flow and pressure fluctuation in axial-flow pumps, and the method can extend to other similar hydraulic machine too.