Determination of Pump Impeller Deflections: Comparison of FSI-Simulations to Measurements

The determination of pump rotor oscillations induced by exciting hydrodynamic forces requires both a solution of the flow field in the pump and an analysis of the structural mechanics of the pump rotor. In the present contribution, simulations which accomplished different coupling methods between the fluid dynamic solution and the structural analysis were carried out for a single-blade pump. In a first approach a one way coupling was used to determine the oscillations of the pump impeller during operation. The forces calculated from the transient flow field were treated as a load acting at the impeller. A comparison of the computed oscillations to measurements showed that in the present case the strong physical interaction between the flow and the impellers structure requires the feedback of the structural analysis to the flow solution to give more meaningful results. In a second approach a simulation was carried out, which accomplished a full coupling of the fluid dynamics and the structural dynamics. Both physics were solved alternating and at least two iterations, one for each physics, were needed to achieve the required coupled response. The calculations were coupled by passing loads across the physics field interfaces. In the present example, for each regarded time step during one impeller revolution, the pressure field acting at the impeller surface was transferred from the CFD solver to the structural solver as the load on the impeller and the computed deflection of the impeller was transferred back deforming the computational grid of the fluid volume.