Studies of the ERCOFTAC Centrifugal Pump with OpenFOAM
Examensarbete för masterexamen
Numerical solutions of the rotor-stator interaction using OpenFOAM-1.5-dev was investigated in the ERCOFTAC Centrifugal Pump, a testcase from the ERCOFTAC Turbomachinery Special Interest Group. The case studied was presented by Combes at the ERCOFTAC Seminar and Workshop on Turbomachinery Flow Pre-diction VII, in Aussois, 1999. It has 7 impeller blades, 12 diffuser vanes and 6% vaneless radial gap, and operates at the nominal operating condition with a Reynolds number of 6.5*10^5 at a constant rotational speed of 2000 rpm. 2D and 3D models were generated to investigate the interaction between the flow in the impeller and that in the vaned diffuser using the finite volume method. The incompressible Reynolds-Averaged Navier-Stokes equations were solved together with the standard k-epsilon turbulence model. Both steady-state and unsteady simulations are employed for the 2D and 3D models. A Generalized Grid Interface (GGI) is implemented both in the steady-state simulations, where the GGI is used to couple meshes of rotor and stator, and in unsteady simulations, where GGI is applied between the impeller and the diffuser to facilitate a sliding approach. Several numerical schemes are considered such as Euler, Backward and Crank-Nicholson (with several off-centering coeffcients) time discretization, and upwind and linear upwind convection discretization. Furthermore, the choice of different maximum Courant Number and the different unsteady transient solvers have been studied, and the required computational time has been compared for all the cases. The ensemble-averaged velocity components and the distribution of the ensembleaveraged static pressure coeffcient at the impeller front end are calculated and compared against the available experimental data provided by Ubaldi. The computational results show good agreement with the experimental results, although the upwind convection discretization fails in capturing the unsteady impeller wakes in the vaned diffuser. The case with a maximum Courant Number of 4 is regarded as having the most effcient set-up, predicting the unsteadiness of the ow with a large time-step.
Strömningsmekanik , Fluid mechanics