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Abstract
Trash racks are set before inlet sumps of a pumping station with wet-pits in order to block trash. The flow fields before and behind the trash rack were numerically simulated and flow fields in the inlet sump were calculated using the simulated velocity distribution of the section behind the trash rack as the inlet boundary condition. Local head loss of trash-barriering increases with the increase of blockage ratio of the trash rack. When waterweeds block upper part of the trash rack, flow pattern behind the trash rack will be extremely turbulent, flow velocity of lower part of inlet section of inlet sump will increase, flow velocity of the upper part will decrease, and even backflow appears, which will deteriorate the flow pattern and increase head loss in the inlet sump. Trash-barriering has little effect on velocity distribution of impeller inlet section. Trash-barriering will not only increase head and power of the pump but also decrease the flow. For the example of the pumping station: when blockage ratios of the trash racks are 0.3, 0.5, and 0.7, operating cost will increase by 13%~43% than that of without trash racks. Therefore, the trash rack should be cleaned up timely.
Highlights
To ensure the safe operation of pump units, the trash rack is often set before inlet passage in pumping station to block trash
There are few studies about head loss and flow field of trash-barriering when trash rack is blocked by trash
When the blockage ratios are 0.5 and 0.7, the water level differences are 0.25 m and 0.69 m and the local head losses are 0.157 m and 0.478 m, respectively, which is consistent with the actual situation of pumping stations
Summary
To ensure the safe operation of pump units, the trash rack is often set before inlet passage in pumping station to block trash. Gao et al [1] calculated and analyzed the flow velocity distributions of inlet and outlet of a pumped storage power station and the head loss without trash in front of trash rack through flow numerical simulation. There are few studies about head loss and flow field of trash-barriering when trash rack is blocked by trash. In numerical calculation we adopted ANSYS CFX software and VOF model [5, 6] to calculate local head loss and flow field before and behind the blocked trash rack of a prototype pumping station. We use velocity distribution behind the trash rack as the inlet boundary condition to calculate and study the influence of trash-barriering on the flow in inlet sump and operation of pump device
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