Because of the long operating time, the efficiency of centrifugal pumps decreases gradually. A decreasing efficiency originates from different wearing processes, meaning that a detailed knowledge of these processes and their influence can be helpful for a smooth operating behavior.
Therefore, the erosion induced by solid particles in a centrifugal pump is investigated experimentally and with the help of computational fluid dynamics. The objective is the numerical prediction of occurring areas of erosive wear and especially their influence on the pump’s performance curves in form of a time-lapse simulation of the pump’s life cycle.
As a fundamental examination of the influence of erosive wear induced by solid particles is investigated experimentally. Therefore, a closed-loop test rig, shown in figure 1, including all metering devices for a standard pump performance test according to DIN EN ISO 9906 has been set up.
When pumping slurry, the machine operates at its best efficiency point with a suspension of water and pure corundum. The solid concentration is one per cent by volume. The pump’s performance curve is measured with pure water at specified time intervals.
The simulations are performed for unsteady conditions and the whole geometry of the pump including all side chambers, sealing gaps and balancing wholes. As the particle concentration is fairly low and the flow conditions inside the pump assume appreciable particle accelerations, the simulations are computed using the Lagrangian method for particle tracking and a one-way coupling.
The erosion induced by solid particles is predicted using different erosion models, e.g. Finnie, Grant-Tabakoff and the in-house model. Since the predicted erosion has no influence on the hydraulic contour, additional routines are developed to implement a dynamic mesh method depending on the predicted damage.
The experimental outcomes in figure 2 reveal a comparable distribution and especially the location of eroded material as predicted by the erosion models. The unilateral damage to the drainage outlet can clearly be identified. Even the non-uniform damage of the volute’s nose is similarly apparent, in detail, in the experimental and numerical results shown in figure 3.
Furthermore, the experimental investigations reveal the influence of slurry erosion wear on the pump’s performance curve as shown in figure 4. To reach the overall objective, the key challenge is to calculate the time-dependent variations of the performance curve numerically in a manageable brief span.