CFD simulation of a sealless pump configuration

In a sealless centrifugal pump configuration a permanent magnet impeller is levitated and driven by an external rotating electromagnetic field. The radial position of the impeller is controlled by a bearingless motor while the axial position should adjust itself passively by balancing out hydrodynamic forces and the restoring force of the impeller's permanent magnet. First, the complex flow situation around a fixed impeller is simulated by means of a three-dimensional unsteady CFD simulation. In contrast to conventional pumps the secondary leakage streams are quite dominant and have to be included into the simulation. Rotorstator interactions are accounted for by sliding meshes. Secondly, based on the complex overall simulation a simplified pump model is derived for further dynamic impeller studies. Hereby, the axial movement of the impeller is described by a simple differential equation balancing magnetic, hydrodynamic and inertial forces. Several meshing strategies (re-meshing, deforming, layering, moving) have to be performed to adapt the computational grid to the moving impeller. As a result of these simulations the dynamic response of the impeller's axial position to sudden changes in rotation speed or pressure head can be studied. Both, fixed and dynamic impeller simulation work well and produce reasonable results. Furthermore, CFD results are in good correspondence with prototype measurements. © 2004 WIT Press.