| Pumps and pipes are the basic hydraulic components of water supply system. For the long-distance pipe water supply system, the following three aspects are worthy of further study:①The numerical simulation of internal flow of double-suction centrifugal pump. Hydraulic performance, cavitation performance and operation stability are the three basic problems for pump design. Normally, the head and the flow of the pumps in the water supply systems along the Yellow River in the northwest region are considerably large, so it is difficult to select proper pump from the existing collection of synthetic characteristic curves of pumps. The performance of pumps is determined by the distribution characteristics of the flow field, so it is important so reduce the pressure fluctuation in the pumps for improving the operation stability of units. Therefore, there is an important theoretical and engineering application value to carry out the numerical simulation of the internal flow in the pump, with which the pump design is optimized and the design cycle is shortened;②The optimization of water hammer protection measurements. For long pipeline system, the phenomena of water column separation and cavity collapsing, which result in huge water hammer pressure, are easy to occur in the local convex point of the pipeline after accident pump-stopping. Therefore, the research on protective performance and optimization method for structural parameters of one-way surge tanks and air valves, which are widely used in water-suply project, is very important to insure the safety of project and reduce the investment of project.③The dynamics of PCCP pipes. Due to the complexity of PCCP pipes structure, the finite element analysis model for PCCP pipes is not yet mature. The structural dynamical response of the PCCP pipes under the pressure of water hammer is complicated. Definitey, the finite element calculations of PCCP pipe and the analysis of structural dynamics are valuable.The 3-D steady full flow passage numerical simulation of double suction centrifugal pumps with staggered impeller is conducted in this paper. According to improved design methods, a double suction centrifugal pump with staggered impeller is designed, and its internal steady flow is simulated by using different turbulence models. Based on the inverse engineering method, the model for foreign real machine with same parameters is mapped and its internal steady flow is simulated as well. Then the comparison between the external characteristics of the designed pump and the foreign real machine is conducted. The results show that for the analysis of external characteristic of double-suction centrifugal pump, there is no distinct difference among the prediction results of the five turbulence model. In order to enhance the simulation accuracy and save computational resources, the SST k-εmodel and the RNG k-ωmodel are chosen to simulate the steady flow field of double-suction centrifugal pumps. The CFD simulation results show that the head of the designed pump, which is based on the improved design method, is slightly higher than that of the foreign real machine, while the efficiency is slightly lower. This indicates that the improved design method is feasible.The LES method is adopted to simulate the unsteady flow of double suction centrifugal pumps with staggered impeller. The averaged head and averaged hydraulic efficiency of the designed pump are closer to those of the foreign real machine, but more calculation time is required than that for steady flow simulation. Under the designed flow conditions, the frequency of pressure fluctuation in the position of double-suction centrifugal volute tongue is consistent with that of blade passing and the different layout of impeller causes different pressure fluctuation value. The simulation indicates that the amplitude of pressure fluctuation in volute tongue of the staggered arranged impeller is lower than that of the symmetrical arranged impeller, but it has a higher frequency. Moreover, the amplitude of pressure fluctuation in volute tongue of the symmetrical arranged impeller is 1.58 times of that of the staggered arranged impeller, which is caused by the uneven pressure distribution on the top of blades of the symmetrical arranged impeller.The basic equations of water hammer and the mathematical models for boundary conditions are derived in this dissertation. The water hammer problems in gravity pressurized water supply system and pumping system are respectively analyzed based on the model. The results show that for a gravity pressurized water supply system with long pipeline, hydraulic friction should be considered in the calculation of valve-closing water hammer; the flow properties of the valve have a great influence on the valve-closing water hammer of the gravity pressurized water supply system. The change curve of the relative opening degree along with the travel opening degree of the end regulating valve should follow the trend of ’first steep then slow’. According to the basic theory of inverse problem of the fluid transient, the optimization model for the closing law of the end valve is established. The calculation results of engineering example show that under the condition of the same total closing valve time, the ’first quick then slow down’closing valve law further increases the trend of’first steep then slow’, which is more effecitive to reduce water hammer pressure and saving construction investment.The main parameters influencing the protective effect of slow shut air valve are the product of intake area and flow coefficient (CinAin), the product of vent area and flow coefficient(CovldAovt), the ratio of limiting plate hole area and intake-vent areaμ, the ratio of absolute pressure in the tube when limiting plate begins to rise and local atmospheric pressure kv and the installed position of air valve. Under the condition that the air valve position is defined according to the terrain, setting the above four parameters and the parameters of the pump outlet valve closure rule as the decision variables, and the minimum water hammer pressure in the pipeline as the objective function, the optimization model of slow shut air valve parameters is established and solved by using Genetic Algorithm.The main parameters influencing the water hammer protection of one-way surge tank are efficient water head, volume of the tank, which is determined by the diameter of the tank under the head-determined condition, and diameter of the fill pipe. Setting the above three parameters and the parameters of the pump outlet valve closure rule as the decision variables, the reasonable reverse rotational speed of the unit and the maximum water hammer pressure of the point behind the pump outlet valve as the constraints, and the minimum volume of one-way surge tank as the objective function, the optimization model of one-way surge tank parameters is established and solved by using Genetic Algorithm.The above two optimization models are adopted to analyze the Ningdong water supply project and proper water hammer protection measurements are raised.The finite element model for PCCP pipe is established based on large-scale finite element software ANSYS in this dissertation. Moreover, the simulation method for pre-stress, the characteristics of the deformation and stress, the natural frequency and the dynamic characteristics under the water hammer waves are investigated. The results show that under the actions of pre-stress, weight, backfill soil pressure, fluid weight and internal water pressure, the elliptical deformation of the PCCP pipe will occur, the stress distributions of medial and lateral layer of inner concrete and medial layer of outer concrete are similar, meantime, the stress distributions of lateral layer of outer concrete and protective layer of mortar are similar. The main stress of inner concrete is in stress state under the action of water pressure. But the layer of the outer surface of the mortar tube is in a big tensile stress. On the other hand, the natural frequencies and modes are different, so the influence of the natural frequency of the system should be considered in piping system, and set the natural frequency and the excitation frequency more different in order to avoid the occurrence of resonance. Dynamical response of the PCCP pipe occurs under the water hammer pressure and the maximum displacement of pipe vibration occurs at the middle part of the tube. When the water hammer pressure reaches the maximum value, the amplitude and stress also get the maximum values, meanwhile, the PCCP vibration response curve is consistent with the changes of water hammer wave.Finally, the prospects of further research are proposed. It is pointed out that research on the coupling mechanism of abrasion and cavitations of double-suction centrifugal pump under the conditions of high sediment based on two-phase flow theory has important theoretical and practical value, which can extend maintenance cycle and increase unit life expectancy. On the other hand, it’s valuable to further analyze and reveal the coupling mechanism of the PCCP and fluid by analyzing fluid-structure interaction under the tight coupling. |
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