The interaction between fluid and structure occurs in a wide range of engineering problems. The solution for such problems is based on the relations of continuum mechanics and is mostly solved with numerical methods. It is a computational challenge to solve such problems because of the complex geometries, intricate physics of fluids, and complicated fluid-structure interactions. The way in which the interaction between fluid and solid is described gives the largest opportunity for reducing the computational effort. One possibility for reducing the computational effort of fluid-structure simulations is the use of one-way coupled simulations. In this paper, different problems are investigated with one-way and two-way coupled methods. After an explanation of the solution strategy for both models, a closer look at the differences between these methods will be provided, and it will be shown under what conditions a one-way coupling solution gives plausible results.

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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.

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