Three-dimensional turbulent numerical simulation and model test of front-shaft tubular inlet conduit of pumping station

Abstract: The tubular shaft inlet conduit is one of the most important structural styles which is suitable for a low-water-head pumping station, and it is gradually widely used in irrigation and drainage of water conservancy projects, such as in the South-to-North Water Diversion Project and Tai-Hu lake treatment project in China. Eighteen large-tubular shaft pumping stations have already been built or are under construction in China since 2004. To meet with engineering demands, research on improving the efficiency of a tubular shaft pump system has been undertaken since the first tubular shaft pumping station Mei-Lianghu was constructed and put into operation. Some results, aimed at every specific engineering project, have been acquired by means of model tests, three-dimensional turbulent numerical simulations, and empirical practice, but a standard design method for the optimized tubular shaft inlet conduit could not be derived from those references until now. In order to derive a feasible design method, three-dimensional turbulent numerical simulation was applied to investigate the internal flow pattern of a certain front-tubular shaft inlet duct which was due to the idea of regular outline design. On the basis of systematic research on the internal flow characteristics about nine variable operating conditions, the streamlines and velocity contours on the horizontal plane and different cross sections were revealed, the uniformity of axial velocity distribution and velocity deflection angle at the pump suction were obtained, and the hydraulic loss of the inlet conduit was also quantitatively calculated. It turned out that the streamlines are good with no vortices, the uniformity of axial velocity distribution is as high as 95.46%, and the axial velocity angle approaches 87.94°. The results also show that the hydraulic loss increases with increasing flow rate, while the loss coefficient decreases. In order to validate simulation results, a small-scale, transparent, Plexiglas model of the inlet conduit was made. Its hydraulic loss was measured and compared with numerical calculation data for nine different volumetric fluxes, and the flow patterns in the inlet duct were observed as well. Test results proved that the hydraulic loss is small，the loss coefficient is 6.249×10-2, and no vortices were found. It also revealed that simulation results are consistent with experimental data. Furthermore, the energy characteristic curves of the model pump set were acquired for five blade angles through the pump set model tests. According to experimental results, we conclude that the model pump set has a higher efficiency across a large range of low-water head, and its peak efficiency is 80.52% with water head 1.83 m and a blade angle of -2.