Comparison of Pump Impeller Orbit Curves Obtained by Measurement and FSI Simulation

Raw sewage water typically contains large amounts of solids and fibers. The transport of water comprising such impurities with centrifugal pumps requires a special impeller geometry, in order to avoid operational disturbances by clogging. Non-clogging sewage water pumps are equipped with impellers featuring a small number of blades. Single-blade impellers comprise the smallest number of blades and provide therefore the biggest cross sections of the flow channel. But there are also disadvantages which occur during pump operation, because the time-variant flow in such pumps results in periodic unsteady flow forces which affect the impeller and which produce strong radial deflections of it. To determine the oscillations of the pump rotor induced by the exciting forces a coupled solution of the flow field in the pump and the structural mechanics of the pump rotor is required. In the present paper simulations which accomplish different coupling methods of the fluid dynamics and the structural dynamics have been carried out. In a first approach an explicit partitioned coupling method with simple interchange of boundary conditions has been applied. This approach disregards the feedback of the structural analysis to the flow and the results comply only roughly to the measurements. In a second attempt a fully coupling of the fluid dynamics and the structural dynamics has been carried out. The simulations are coupled by sending the computed flow forces at each time step as the load to the solver of the structural mechanics and the computed deflection of the impeller acts as a deformation of the computational grid of the fluid volume. The impeller orbit curves obtained by this method compare much better to the measurements.