Research On Hydraulic Performance And Multi-objective Optimization Design Of Low-lift Pump System

Low-lift pump system is an important modern water infrastructure, which plays a key role in many fields, such as inter-basin water transfer project, drought resistance of farmland and region, urban flood control and drainage, urban water supply, wastewater discharge and so on. With the development of national economy and energy consumption is emphasized by government, people hope the hydraulic performance of pump system become better and better. The hydraulic performance and multi-objective optimization design of pump system with low-lift based on the methods of theoretical analysis, numerical simulation and physical experiments. The main research contents and creative achievements are as follows:(1) The structure classification and characteristics of low-lift pump system were briefly introduced. The present results, progress and methods in its research were analyzed and summarized from four aspects, such as impeller, guide vane, inlet outlet passage and pump system. In order to offer technology support for further study, automatic solving program of hydraulic performance of pump system was implemented using the Matlab software, and combining traditional Visual Fortran with AutoCAD graphics software, the Bezier curve drawing program was developed which is human-computer interaction interface, to achieve the purpose of computer automated drawing of experimental data. A lot of numerical experiments have been done with the choices of turbulence model, mesh number and mesh type for studying the suitability of numerical simulation for low-lift pump system. The predicted data of numerical simulation and model test were compared for providing a reliable performance prediction method. Focusing on the effects of blade tip clearance on the numerical simulation of inner flow field of pump system, the effect of blade tip clearance on the flow rate, head, torque and efficiency of pump system were analyzed, and the structure of leakage vortex was captured and analyzed. When the tip clearance is not larger than0.3mm, blade tip clearance has little influence on the external performance of pump system. With the increase of blade tip clearance, head and efficiency drop quickly. When the blade tip clearance reaches to1.0mm, the decrease range is10%-27%and the efficiency is decreased by about10%. Blade tip clearance is one of physical boundary conditions for numerical simulation of pump system, which should be considered.(2) The Mutual coupling effect of inlet passage and impeller, guide vane and outlet passage analyzed in detail based on CFD. Outlet circulation of guide vane has great influence on flow pattern in the outlet passage. The flow distribution for both sides of the dividing pier is not symmetric, especially for small flow rate condition, the helical flow occurs at the right side of dividing pier. The effect of the residual circulation of outlet section on the outlet passage with and without pier was analyzed firstly based on the whole pump system. Under the condition of zero velocity circulation, the hydraulic loss of outlet passage is in proportion to the square of flow, and the hydraulic loss is larger than that with velocity circulation. The effects of flow guide cone on the hydraulic performance of inlet passage and the effects of guide vane on the performance of pump system were analyzed for reversible vertical pump system. According to the design method of diffusion guide vane of bulb tubular pump, the effects of diffusion guide vane on the reversible vertical pump system and applicability problem about it were analyzed. A physical model test was adopted to study the characteristics of pressure fluctuation of reversible pump system by performance and cavitation test. (3) The relation between hydraulic performance of outlet cross sections with rotating impeller and the relative height of outlet cross sections and the stress distribution of impeller were analyzed, as well as the relative velocity distribution near the airfoil cross sections under the designed condition. The hydraulic moments were calculated based on the numerical results under different conditions, and the changing features of hydraulic moment on blades with flow rates were analyzed firstly. The reference nominal height of pump system was given. According to the characteristics of urban flood protection and drainage pump system, two sets of dividing tubular pump systems with symmetric aerofoil blade were developed. The effect of bulb section on the hydraulic performance was analyzed, which included the hydraulic loss of bulb section, the internal flow of guide vane and the hydraulic performance of "S" shape impeller vane. C.P.I (comprehensive performance index) is introduced firstly to analyze the difference between two sets of pump system. Structure size of pump system provided a reference for dividing tubular pump system. In order to study on the evolution law of shaft profile line and the influence relation between the hydraulic performance of pump system and shaft line,4different shaft inlet passages were designed with one-dimensional hydraulic design method based on the induction analysis of shaft profile lines. The CFD software ANSYS CFX was used to simulate the three-dimensional fluid flow of pump system. The expression of the functional relations between the efficiency of pump system, flow rate and three performance index of inlet passage were deduced based on the multiple linear regression analysis method. Due to the joint influence of the hydraulic loss, the axial velocity distribution uniformity and the velocity-weighted average swirl, the flow chart was put forward that is about multi-objective collaborative optimization of inlet passage. At the optimum operating condition, the distributions of axial velocity in different outlet section have same tendency, and polynomial mathematics model was used to fit out the distribution of axial velocity. Based on the three dimensional steady numerical simulation, dimensionless momentum parameter and the weighted performance of multiple operating conditions evaluation method (M.P.I) were solved to the hydraulic performance comparison of different pump systems. ANSYS CFX is applied to carry on the three-dimensional numerical simulation on the whole flow passage of the shaft tubular pump system of front-position, post-position. The hydraulic performance of different inlet and outlet passage and the external characteristic of two sets of pump system are compared and analyzed quantitatively in detail for introducing the average swirl angle.(4) Based on theoretical analysis of the hydraulic performance of inlet and outlet passage, Multi-objective optimization mathematical models of inlet and outlet passage were proposed firstly. In order to provide the new multi-objective and multi-constraint optimization techniques method for passage optimal design, automatic optimization platform of inlet and outlet passage were built firstly based on the optimization software iSIGHT-FD. In the paper, inlet and outlet passage of shaft extension tubular pump system were taken as optimization objects by using optimization platform, which were described by the geometric mathematical model. For optimized inlet passage, the hydraulic loss decreased by12.61%, the axial velocity distribution uniformity improved by1.86%, and the velocity-weighted average swirl angle increased by3.10°. For optimized outlet passage, the hydraulic loss reduced by24.91%, kinetic energy recovery coefficient improved by6.65%, and equivalent diffusion angle is9.98°. According to quantitative analysis of the optimization results, the automatic optimization platform is feasible. Based on the optimized design of passage, multi-objective optimized mathematic model of pump system was proposed firstly, and flow chart of automatic optimization was given.(5) For new S-shaped shaft extension tubular pump system, the distribution of static pressure, skin friction line of the blade surface, and the distribution of static pressure and vortex in the guide vane were analyzed qualitatively, based on the steady numerical simulation. The distribution law of axial velocity of impeller outlet, recovery circulation and hydraulic loss of guide vane outlet were analyzed quantitatively. The paper pay attention to the detail of the flow field in the inlet and outlet passage includes the distribution of velocity and static pressure. With the increase of flow coefficient, the axial velocity distribution uniformity and the velocity-weighted average angle increase gradually. The velocity-weighted average angle is88.8°, the axial velocity distribution uniformity is97.51%and the hydraulic loss is3.89cm at the optimum operating condition KQ=0.490. Because of the relative motions between impeller and guide vane, the technology of the transient rotor stator (TRS) was applied to simulate the pressure fluctuation of interior flow in the new high efficient S-shaped shaft extension tubular pump system and maximum and minimum static pressure on the blades of the impeller and guide vane.A physical model experimental research on energy performance, cavitation performance and runaway characteristics of the pump model system has been conducted on the high precision hydraulic machinery test stand of Jiangsu province. The highest efficiency of the new S-shaped extension pump system is83.55%at the blade angle-2°, which has significant advantages of high efficiency and energy-saving. The comprehensive hydraulic performance of the new S-shaped extension pump system reaches international leading level. Through the calculation of resistance torque, the variable factor of a unit runaway speed with same blade angle is analyzed under different working conditions of reverse-water-head. The unit runaway speed obtained from model pump system is applicable and safe for conversion to prototype pump system.Two electro acceleration sensors were set on the outer wall of guide vane for studying the operation stability of new S-shaped shaft extension pump system, and the vibration displacement of X direction and Y direction were analyzed at the rotation speed1350r/min. Signal collecting analyzer EN900is used to study the operation stability of model pump system at blade angle+4°and-4°.(6) The internal flow mechanism of cube-type axial-flow pump system was studied under vortex inflow for the first time. The influence of bottom clearance of flare tube is related with the passage height on the internal flow and hydraulic performance of cube-type inlet passage was analyzed. The axial force and radial force of the impeller were mainly analyzed under vortex inflow. The influence of submerged vortex on the pressure fluctuation of impeller inlet in different operating conditions was mainly analyzed. The evolution process of submerged vortex generation and the gradual dissipation was studied by the quantitative method. The3D-PIV measurement technique and high-speed camera were adopted in experiments. By compared testing data with computational results, it is found that the results of numerical simulation are in satisfactory agreements with experimental data, which validates the numerical results to be reasonable.(7) The effects of inlet guide vane on the hydraulic performance of pump system were analyzed by the method of velocity triangle. According to the design requirements of inlet guide vane, adjustable inlet guide vane was designed, and3D steady numerical simulation of pump system was simulated in different adjustable angle of inlet guide vane. This paper mainly studies on the effects of inlet guide vane on the external and internal characteristics of pump system and the hydraulic performance of impeller. Synthetic characteristic curve of pump system with inlet guide vane was obtained by self-compiling program. By establishing mathematical model of multivariate nonlinear regression model, the external characteristic data can be obtained in the different adjustable angle. The effects of adjustable outlet guide vane on the performance of pump system and the internal flow pattern of guide vane were analyzed based on CFD. BP-ANN mathematic model was established for predicting the external performance, and the combined method was used to verify the feasibility of adjustable outlet guide vane.