Influence Of Discharge And Circulation On Head Loss Of Outlet Conduit In Vertical Pump System With Low Head

In our country, water resource is distributed much unevenly in time and regions, and floods and droughts happen frequently, which is seriously preventing the economy of our society from sustainable developing and the living standard of our people from continual improving. Entering the21st century, lots of hydraulic projects, the core of which are large and middle pumping stations, are being constructed in our country, such as the East Route Project of South-to-North Water Diversion Project, for the allocation of water resources and the resistence against floods and droughts. Among these pumping stations, large ones with low head play a very important role. These pumping stations have distinctive characteristics which are the head is low, the discharge is large and the operating time in every year is very long. In view of the importance of South-to-North Water Diversion Project and other projects, high standard, which is these pumping stations should be operating with safety and stability, meanwhile the efficiency of pump system be high, is put forward.Pump sysytem is the core of the pumping station, which is consisted of inlet conduit, pump and outlet conduit, and these three parts complement each other and they all are important. The outlet conduit is the transition part between pump impeller chamber and outlet sump. The main function of outlet conduit is to make flow change direction orderly and diffuse gently and under the condition of no flow seperation and vortices, recover flow kinetic energy as much as possible. The hydraulic performance of the outlet conduit is one of the important factors that decide whether pumping stations could operate with safety, stability and high efficiency.Head loss is an important index that measures the hydraulic performance of outlet conduit. It has been a consensus that discharge has an important influence on head loss of the outlet conduit, however, another important factor that affects the head loss of the outlet conduit is circulation and it does not attract enough attention. As for rotation of the impeller, flow from the guide vane outlet gets certain circulation, and it makes flow in the outlet conduit move spirally. With discharge and circulation affecting together, the law of the outlet conduit head loss becomes very complicated.On the basis of former relevant researches, in this paper, the head loss of the outlet conduit in pump system under diffierent conditions is discussed.In this paper, test method and numerical computation method are combined in this research, and main contents are as follows:(1) Specially designed test device system is adopted, and the outlet conduit of a certain pumping station in the East Route Project of South-to-North Water Diversion Project is treated as the research object, and the test is carried out under diffierent conditions to test and research the head loss of the outlet conduit.(2) Fluent, which is a commercial numerical calculation software, is used to simulate the3D turbulent flow in the outlet conduit under normal operating conditions.(3) Based on the test and the numerical computation results, the law of the joint influence of discharge and circulation on the outlet conduit head loss is analyzed and sumerized.The main conclusions are obtained as follows:(1) As for a certain pump system, along with the increase of discharge, circulation decreases in the beginning and then increases, and the smallest circulation appears under the operating condition smaller than the design one.(2) As for a certain pump system, The average swirl angle of water at the guide vane outlet is changed with a certain law when the discharge is changed, and this law is that in the discharge range of0.4-0.8times of the design discharge, the average swirl angle is decreased when the discharge is increased while under normal operating conditions, the average swirl angle is changed very little.(3) As for a certain pump system, in the discharge range of0.4-0.8times of the design discharge, along with the increase of discharge, the head loss of outlet conduit is decreased a little. Under normal operating conditions, the head loss of outlet conduit is increased along with the increase of discharge.(4) The head loss of the outlet conduit is affected by discharge and circulation together. Dischrage is the main reason that causes the head loss, while circulation affects the head loss mainly by affecting the flow pattern.