Erosion Estimation for the Impeller Blades of Centrifugal Dredge Pumps

Abstract

The constant impingement of sand particles on the wetted surfaces of a centrifugal dredge pump causes the performance of the pump to deteriorate. Therefore, components or complete pumps have to be replaced after some time. The use of numerical models to estimate the erosion wear in centrifugal dredge pumps can give insight into the principal erosion zones and the magnitude of the erosion in those zones. This information can be used to increase the erosion resistance of pump components. In addition, instructions for the maintenance of the pump can be composed based on the expected erosion wear. In that way, the efficiency of dredge processes can be increased considerably. This Master's Thesis project is carried out by the author during a 12-month period at Damen Dredging Equipment in Nijkerk, The Netherlands. The focus of the project is on developing, validating and demonstrating a numerical model capable of estimating the erosion wear due to slurry flow on the impeller blades of a centrifugal dredge pump by using Computational Fluid Dynamics (CFD). Within the CFD framework, it is found that the appropriate model for calculating the flow of the slurry (water with sand particles) is the Eulerian-Lagrangian method. The numerical computations are performed using the commercial software ANSYS Fluent. For the turbulence of the water, the k-ω SST turbulence model is used. The collisions of the particles with the wall are modeled using the Grant-Tabakoff model, whereas the linear soft sphere model is used for the inter-particle collisions. Using the aforementioned combination of models several studies are conducted, starting with a validation study using a submerged impinging jet benchmark. From that study, it is found that the fluid and particle velocity fields can be calculated with reasonable accuracy. For the same type of problem, the numerical erosion profile is compared to experimental values. It appeared that there is a considerable dependency of the erosion profile on the material hardness. In addition, the result of the four-way coupled method is influenced to a large extent by the values of the collision model parameters. By comparing the resulting erosion profile from the two-way coupled model with the experimental erosion, a good qualitative agreement is found. However, the magnitude of the erosion is overpredicted by this model. In addition, a verification and validation study was performed for the impeller. For the latter, new experiments were conducted in a facility that is available within the company Damen Dredging Equipment. By measuring a number of points before and after a 56 hour experiment, the resulting erosion could be determined. The four-way coupled computation for the impeller could not be fully completed within this project. However, the two-way coupled numerical model showed good correspondence with the experimental results. The currently available model is capable of predicting the maximum erosion zones on the impeller blades. This information could for example be used to improve the design of the impeller or to get a first order estimation of the lifetime of an impeller. The applicability of the numerical model that is developed during the current project can be extended by for instance including the pump volute.