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 periodically unsteady flow fields in a low specific speed radial diffuser pump have been investigated both numerically and experimentally for the design condition (Qdes) and also one part-load condition (0.5Qdes). Three-dimensional, unsteady Reynolds-averaged Navier–Stokes equations are solved on high-quality structured grids with the shear stress transport turbulence model by using the CFD (computational fluid dynamics) code CFX-10. Furthermore, two-dimensional laser Doppler velocimetry (LDV) measurements are successfully conducted in the interaction region between the impeller and the vaned diffuser, in order to capture the complex flow with abundant measurement data and to validate the CFD results. The analysis of the obtained results has been focused on the behavior of the periodic velocity field and the turbulence field, as well as the associated unsteady phenomena due to the unsteady interaction. In addition, the comparison between CFD and LDV results has also been addressed. The blade orientation effects caused by the impeller rotation are quantitatively examined and detailedly compared with the turbulence effect. This work offers a good data set to develop the comprehension of the impeller-diffuser interaction and how the flow varies with relative impeller position to the diffuser in radial diffuser pumps.

This contribution is addressed to the periodically unsteady flow forces of a single-blade sewage water pump, which affect the impeller and produce radial deflections of the pump shaft. The hydrodynamic excitation forces were calculated from the time dependent flow field, which was computed by numerical simulation of the three-dimensional, viscous, time-dependent flow in the pump. A commercial computer code was used to determine the time accurate Reynolds averaged Navier-Stokes equations. The transient radial flow forces at all time steps for a complete impeller revolution affect the rotor of the single-blade pump and stimulate it to strong oscillations. To determine the influence of the vibration stimulation forces on the dynamic behavior of the pump rotor, an investigation of the rotor’s structural dynamics was accomplished. A dynamic time analysis for the pump rotor provided the dynamic answer from the structural model of the rotor under the influence of the flow forces. The hydrodynamic forces, which were calculated before, were defined as external forces and applied as the load on the rotor. The resulting impeller deflections were calculated by a transient analysis of the pump rotor system using the commercial finite element method software PROMECHANICA. To verify the results obtained by standard numerical methods, the radial deflections of the impeller of a commercial sewage water pump, which has been investigated numerical in advance, were measured for the horizontal and for the vertical coordinate direction by proximity sensors. The measured data were compared to the computed amounts for a wide range of pump operation. The results show a good agreement for a strong part of an impeller revolution for all investigated operating points. The simultaneous measurement of vibration accelerations at the outer side of the pump casing showed the effects of the time-dependent flow, which produce hydrodynamic forces acting at the impeller of the pump and stimulating it to strong oscillations.

In this paper, the periodically unsteady pressure field caused by rotor-stator interaction has been investigated numerically by computational fluid dynamics (CFD) calculation to evaluate the transient pressure variation in a single-blade pump for multiconditions. Side chamber flow effect is also considered for the simulation to accurately predict the flow in a whole-flow passage. The strength of the pressure fluctuation is analyzed quantitatively by defining the standard deviation of the pressure fluctuation of a revolution period. The analysis of the results shows that higher pressure fluctuation magnitudes can be observed near the blade pressure side and high gradients of fluctuation magnitudes can be obtained at the trailing edge near the pressure side of the blade. An asymmetrical distribution of fluctuation magnitudes in the volute domain can be clearly obtained. On the cylindrical surface around the impeller outlet, although the absolute pressure value is higher for the Q = 11 l/s condition, the magnitude distribution of fluctuations is lower, and a relatively symmetrical fluctuation distribution is obtained for the Q = 22 l/s condition when clearly asymmetrical distributions of fluctuation magnitude can be observed for the design point and for large flow rates. Obvious periodicity can be observed for the pressure fluctuation magnitude distribution on the circumference with different radii in the volute domain, and some subpeaks and subvalleys can be found. The effects of unsteady flow in the side chambers on the entire passage flow cannot be neglected for accurately predicting the inner flow of the pump. The results of unsteady pressure fluctuation magnitude can be used to guide the optimum design of the single-blade pump to decrease the hydrodynamic unbalance and to obtain more stable performance of the pump.