Study On Pump Set Characteristics Of Low-water Head Large Pumping Station

Based on the background for construction of East Route Project of the South-to-North Water Transfers, major project of city flood prevention and large pumping station reconstruction, this paper focuses on low-water head large scale pumping station. The internal flow pattern and hydraulic performances of new suction-boxes and discharge passages were systemically studied by applying three-turbulence numerical simulation technique and experimentation. The design criterion and methods were brought forward about how to determine reasonable outline and control parameters about new suction-box and outlet conduit. The hydraulic loss of three ordinary outlet conduits was also tested, compared and analyzed. The new property predication mathematical model of pump set performances were theoretically deduced and set up. This paper also systemically does research on transient process during starting period and pump stopping. The complete starting dynamic characteristic mathematical model and a group of new pump stopping dynamic characteristic equations were created. The main work and achievement details are as follows:1. The Reynolds-Averaged Navier-Stokes (RANS) equation was applied for the simulation of 3D flow field in bell-like, shaft tubular and dustpan shaped suction box of large pumping stations. The standard k-s turbulence model based on the Boussinesq hypothesis and SIMPLEC algorithm were adopted in the calculation. Velocity distribution uniformity, velocity-weighted average swirl angle and hydraulic loss magnitude were treated as value objective function during studying on internal pattern and hydraulic loss characteristics of bell-like intake conduit with different suction open heights. The optimization suction open height range was obtained. Constructing model apparatus system of bell-like suction box, the outlet section velocity distribution was measured by probe under various suction open heights. By comparing with computational results, the velocity distribution law of outlet section equipped with pump was revealed. According to the indicated internal flow pattern, velocity on special cross profile and hydraulic loss by numerical simulation and hydraulic characteristics by test, the optimum outline and "control dimensions about shaft tubular and dustpan shaped suction box were attained.2. Based on three-turbulence numerical simulation technique, the internal pattern and hydraulic characteristics were studied about new style outlet conduit namely called tank-like outlet passage which has been used in special low-water head city flood prevention pumping station for recent years. The different schemes of outlet open height, diffusion trumpet-like duct outline, the distance from back-wall to shaft center and no diffusion tube were designed with outlet cone or without outlet cone. By simulating each scheme internal flow field, the position and pattern of various types of vortices were predicted , the friction coefficient about various schemes are obtained and the law of hydraulic loss was also predicted and analyzed. Constructing model apparatus system and making physical models, each scheme hydraulic loss was measured and the variation law of hydraulic loss went with different geometry parameters came to light. According to numerical simulation and experimental results, the optimum design method about new style tank-like outlet conduit was put forward. The siphon discharge passage, straight outlet tube and bell-like outlet passage physical model were designed and made, three outlet passage hydraulic loss were measured and compared.3. Based on hydromechanics theory, the similitude methods for the model test of pump set characteristics, cavitation characteristics and runway speed characteristics were analyzed by applying the equation analytical method of analogy theory. The similarity criteria of parameters scaling laws and key points between the model experiments and the prototype experiments were set forth. The expressions of mechanical efficiency, hydraulic efficiency, cubage efficiency and overall efficiency for pump and pump set were given through theoretical analysis. Considering model pump or pump set experimental data, the constant coefficient used in the overall efficiency formula were obtained through least-square technique and Newton-Raphson method. From the view point of the new efficiency formula, the overall efficiency can be decomposed and each component should be converted alone between hydraulic model and prototype. According to analogy theory, the new conversion methods of mechanical efficiency, hydraulic efficiency, cubage efficiency, pump overall efficiency and pump set efficiency were put forward. The dynamical characteristics prediction mathematical model of low-water head pumping station was set up.4. Based on theoretical analysis of aerodynamic characteristics of the discharge pipeline, transient electric and dynamic characteristics of low-water head pump set, the transient parameters were systemically studied about straight discharge pipe with valve gate breaking flow, siphon outlet passage and straight discharge pipe with quick-stop gate breaking flow during starting period. The mathematical model of transient parameters was put forward for unsteady flow in low-water head pumping installation.5. Based on incompressible water hammer theory, the pump apparatus hydraulic characteristics and pump-unit dynamic characteristics were analyzed and expressed. By utilizing the mathematical model of least square surface fitting of a rectangular region and computer simulation technology, the universal complete pump characteristics was simulated. In order to introduce complete characteristics curves into computation, for the first time transient water head was decomposed into steady condition water head and inertia water head, accordingly water resistance moment and thrust bearing friction moment were also divided into steady condition moment and inertia additional moment. Finite-difference non-linear coupled equations of transient process were established in tubular pumping station while accidental pump-stopping happens or while pumping off with quick-stop gate breaking flow and Newton-Raphson iterative method was used to solve. The mathematical model was applied to simulate the transient process of actual pumping station of the east route of South-North Water Diversion Project during pump stopping.