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(a) Sketch of the scaled pumping station with a dry installed pump. the grey areas mark the two areas of interest, aoI1 and aoI2. (b) Simplified sketch of the suction pipe. aoI1 and aoI2 are the two areas of interest. l and r mark the left and the right part of the suction pipe.
Source publication
Accumulations of sanitary textile materials often lead to clogging of pumps in the wastewater system. Simulation of clogging phenomena may help to identify means of reducing the risk of clogging. In order to provide realistic initial conditions for clogging simulations, this study characterises textiles in artificial wastewater in the suction pipe...
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Citations
... Finally, simulations of the rag transport in a waste water pump have shown to give stable and consistent results, as well as good insight on the probability of occurrence of clogging. Jensen et al., 2018) have attempted to characterize and quantify experimentally the mechanisms that lead to blockage, it has proven very difficult to understand the behaviour of such solid wastes. The rate of accumulation of these thin flexible structure is known to depend on the flow conditions, so that the effectiveness and consequences of more subtle pump design changes are difficult to assess without accurate computational tools capable of capturing both solid and liquid phases. ...
This paper presents a Fluid-Structure Interaction (FSI) model based on an Immersed Boundary Method (IBM) which is applied to the transport of rags in waste water pumps. The IBM is used both to handle the flow in presence of moving rigid solids with arbitrary geometries, and to couple the fluid equations with the structural dynamics of flexible slender solids. The whole FSI model involves the combination of four numerical blocks: (i) a Lattice-Boltzmann solver for the fluid equations, (ii) a solid solver to solve the structural dynamics (if flexible solids are considered), (iii) the IBM to perform the coupling fluid-solid, and (iv) collision models for the coupling solid-solid. The present IBM is based on a direct-forcing approach available in the open-source library Palabos. In the first part of this paper, the accuracy of the IBM is assessed for single-phase flow applications. Particular attention is paid to the prediction of integrated and averaged quantities. The results show good agreements with experimental data. The second part deals with the validation of the proposed FSI-IBM model for solving the interactions between the fluid and flexible slender structures. Quantitative and qualitative comparisons have been carried out against benchmark cases and have demonstrated the good stability and accuracy of the model. The proposed collision models are also assessed in terms of stability and relevance. Finally, simulations of the rag transport in a waste water pump have shown to give stable and consistent results, as well as good insight on the probability of occurrence of clogging.
... Most attempts to characterise blockage in pumps and the impact on hydraulic performance, to date, have relied on experimental studies [3][4][5][6][7][8][9] and only few have employed computational simulations primarily because of the challenge of dealing with the multiple scales when modelling solid-solid collision/contact, turbulent flow and solid interactions and structural deformations. Fig. 1 illustrates three hydraulic blockage types captured by a high-speed camera and classified by Connolly [9]. ...
Sewage water is typically made up of complex liquid mixtures carrying a wide range of suspended solids and materials. Handling of such mixtures can present a significant challenge for hydraulic equipment and pumps in particular. A computational model has been developed to simulate the transport and deformation of immersed thin flexible structures in response to transient fluid loading and interactions with moving and static surfaces in confined domains. The numerical solution is based on an Eulerian-Lagrangian formulation. The Navier-Stokes equations are solved using a segregated approach relying on an iterative form of the PISO pressure-velocity coupling implemented in the OpenFOAM®. The dynamic deformation of the solid are solved using a Finite Difference resolution of the variational derivative of the deformation energy for the solid modelled as a thin flexible two-dimensional membranes with the coupling based on a diffused Immersed Boundary Method (IBM). Turbulence is modelled with a hybrid RANS LES approach which has been shown to better resolve the turbulent eddy structures within the volute than a pure RANS method. The methods and solvers have been detailed and validated in recent publications, but this article is the first detailed characterisation of rag dynamics under varying conditions. The case studies presented will focus on a single blade impeller (SBI) and a two blade impeller (TBI) radial pump. Impeller eye and volute recirculation blockage have been captured giving useful insight into the dynamics of the rag and its interaction with the impeller and volute. The study also highlighted the limitation of the approximate solid-solid interaction model in more sensitive leading edge blockage. Sensitivity analysis on rag length, rag ratio, rag stiffness and flows rate revealed that generally the probability of the blockage increases with the rag length and aspect ratio and decreases with the rag stiffness and flow rate. The complexity of the volute and impeller geometry has a significant impact on the possibility of clogging.
... Pump optimization for this type of application often involves some form of compromise between hydraulic efficiency and anticlogging performances. A few studies [1][2][3][4][5] have attempted to characterize and quantify experimentally the mechanisms that lead to blockage and their impact on pump hydraulic performance. It has proven very difficult, however, to understand the behavior of thin flexible structures, so that the effectiveness and consequences of more subtle pump design changes are difficult to assess. ...
This paper describes a fluid-structure interaction (FSI) model for the study of flexible cloth-like structures or the so-called rags in flows through centrifugal pumps. The structural model and its coupling to the flow solver are based on a Lagrangian formulation combining structural deformation and motion modeling coupled to a sharp interface immersed boundary model (IBM). The solution has been implemented in the open-source library OpenFOAM relying in particular on its PIMPLE segregated Navier-Stokes pressure-velocity coupling and its detached eddy simulation (DES) turbulence model. The FSI solver is assessed in terms of its capability to generate consistent deformations and transport of the immersed flexible structures. Two benchmark cases are covered and both involve experimental validation with three-dimensional (3D) structural deformations of the rag captured using a digital image correlation (DIC) technique. Simulations of a rag transported in a centrifugal pump confirm the suitability of the model to inform on the dynamic behavior of immersed structures under practical engineering conditions.
Improper disposal of wipes results in significant sewer blockages, especially during the COVID-19 pandemic. However, the formation and growth of wipe blockages and their backwater effect in sewers have not been studied. This study employed a vertical rod to simulate sewer obstructions such as tree root intrusion in sewers. Stochastic interactions among wipes, turbulent flow, and the obstruction were experimentally studied in a circular pipe (diameter D = 25 cm), with systematic variations in flow Froude number (Fr), wipe length (L), flow depth (H), submerged rod length (hrod), and rod diameter (drod). It was found that the mean area ratio of wipes (ratio of projected area in water to original surface area of the wipe) ranged from 0.14 to 0.30, indicating the distorted shapes in water. The entrapment probability P (ratio of entrapped to released wipes) for a single wipe was closely correlated with Fr, H/D, L/H, drod/H, and hrod/H, with a maximum value of 0.90. With the increase in the number of wipes released, the influence of the obstruction on wipe accumulation processes became negligible. New equations were developed for characterizing entrapment probability, blockage length, and backwater rise, which can be used to predict the development of wipe blockages and sewage levels. Based on the research findings, policy and management strategies were proposed for wipe blockage reduction in sewers.
As personal care wipes become increasingly popular, inappropriate disposal to the sewage system is raising significant environmental and economic concerns. Many common brands, while marketed as “flushable,” do not degrade appreciably in the plumbing and piping fixtures that the sewage transits. As such, these wipes can cause a myriad of problems including sewer blockage and destruction of pumps and grinders. This work sought to better understand key factors influencing the onset of such problems, including the volume of wipes present in the sewer and the degradation rates associated with a variety of personal wipe products, both “flushable” and nonflushable. The results suggest no correlation between the quantity of wipes in sewage and either the preceding precipitation or the sewage flow rate. To examine their degradability within a sewer system, we evaluated the degradation over time for six commercially available wipes under four conditions: static, kinetic, tap water, and sewage water. Five of the six wipe types were greater than 93% intact after 48 h of exposure to sewer‐like conditions and only one wipe type degraded to less than 14% of its initial volume after 48 h, which is similar to the degradation performance of tested toilet paper. Degradation rates were highest in tap water under kinetic conditions and lowest in raw sewage water under static conditions.
