不同形状的泵站封闭式进水池喇叭口水力性能模拟与验证

Simulation and validation of hydraulic performance of closed-style pump sump with different bell-mouth shapes

泵站封闭式进水池是泵站常用的进水建筑物,喇叭口距水泵叶轮室最近,其形状对水泵性能的影响最为敏感。基于定常不可压缩流体的控制方程和重整化群湍流模型应用SIMPLEC算法,定常模拟不同喇叭口形状的泵站封闭式进水池内水流流动。研究表明,喇叭口对叶轮的进水流态有重要的导流整流作用;过小的喇叭口会严重影响叶轮的进水流态,随着喇叭口逐渐增大,叶轮进口处的进水流态越好,水力损失越小;过大的喇叭口水力损失大,同时需加大池宽,增加了土建投资。喇叭口大小相同,口形1/4圆弧的喇叭口较口形为1/4椭圆的喇叭口,管内流速分布更均匀,流态越好,水力损失较小。计算结果与试验数据在设计工况点处吻合较好,相对误差仅为1.7%,表明计算结果可靠。基于研究结果,推荐工程中喇叭口形状采用1/4圆弧,圆弧半径为叶轮直径的1/3~1/2倍。

Closed-style pump sump is a kind of inlet structures of pump station. Bell-mouth, a part of axial-flow pump system, is used to adjust the velocity distribution on the inlet section of pump. The shape of bell-mouth is an important factor that can affect the hydraulic performance of pump system. In order to investigate the hydraulic performance of different shapes of bell-mouth,the three-dimensional fluid flow inside an axial-flow pumping system was simulated based on the Reynolds time-averaged Navier-Stokes equations, the RNG k-e turbulent flow model, the SIMPLEC algorithm and the law of the wall. The parameters values of closed-style pump sump were from literature including sump length, sump width, bottom clearance, back wall distance, and submergence depth. In order to exclude the possible influence from closed-style parameters, these parameters values were fixed based on design standard of sump. Seven schemes with different bell-mouth shapes were designed with that without bell-mouth as control（scheme 1）. The drawing line of bell-mouth shape in scheme 2- 5 was 1/4-shaped arc with different radius, while the drawing line was 1/4 ellipse line with different axis lengths in scheme 6 and 7. The results illustrated that excessively small bell-mouth may lead to one-way inflow trend in the suction pipes. As the radius of bell-mouth gradually increased, the axial velocity of the suction pipe became more uniform and the hydraulic loss became smaller. Overlarge bell-mouths would lead to more hydraulic loss, larger width of the inlet sump and more investment of civil construction. When the size of bell-mouth were of same dimensions, the flow velocity distribution into the 1/4-shaped arc flare tubes mouths were more uniform and better than that of the 1/4-shaped elliptical flare tubes and had less hydraulic loss. The result of numerical simulation was consistent with the experimental results. The maximum relative error between the simulated value and experimental value in head was 9.8%, and that in efficiency was 13.6%. The relative error of head between the simulation and experiment was 1.7% in the design point with discharge of 0.035 m3/s, which was less than 5%. The relative error of efficiency between the simulation and experiment was 1.1%, which was also less than 5%. It indicated that the results were credible and the results here could be applied to engineering practice. The recommended drawing line of bell-mouth was 1/4-shaped circle and the recommended radius was 1/3- 1/2 of impeller radius.