Numerical Simulation And Experimental Research On Hydraulic Characteristics Of Siphon Rectifiers

With the rapid development of industry and agriculture,the scientific water transfer has always been an im,portant subject in the world.The diversion of the open channel,the diversion of tunnel and the water diversion of the pipe are widely used in the water diversion project.As a common water conveyance system in pipeline diversion,siphon water conveyance system has the advantages of increasing the flow of water,raising the height of distribution and reducing the loss of water head compared with other water conveyance systems.On the basis of the conventional siphon water conveyance system,a new type of submersible rectifier is applied to the entrance of the pipeline.Its advantages are that it can improve the flow state in the tube,reduce the overall resistance coefficient of the pipeline and reduce the formation of the suction vortex,and thus improve the sexual energy of the siphon water conveyance system.Although the siphon rectifier has been widely used in practical engineering,its working principle has not been f'ully revealed.The rectifier design lacks theoretical guidance and the internal structure is more complex,resulting in high local resistance loss and a certain impact on the efficiency of water transport.In this thesis,a submersible rectifier applied to the inlet of the siphon water pipeline was studied.The flow state and resistance characteristics of the diffused jet tube in the rectifier and its internal fluid domain were analyzed by the combined method of experimental research and numerical simulation.The structure of the diffused jet tube,the length of the converging section,the angle of the contraction and the mode of the array were optimized by the method of orthogonal analysis and factor analysis.,and the self-absorption characteristics were studied.The main contents and innovations of this thesis are as follows:(1)According to the special structure of the submersible rectifier,the numerical simulation of a single diffused jet tube was carried out.Through the simulation results,the effects of the grid size of different near wall surface,the number of the near-wall mesh nodes,the gradient of the grids and the turbulence models on the resistance characteristics of the single pipe were compared,and the best simulation scheme was determined.The orthogonal test of single jet tube structure was designed by orthogonal design.Based on CFD,the resistance coefficient,the velocity of internal flow field and the distribution of turbulent kinetic energy were analyzed,and the optimal structure of the diffused tube was obtained.The axial velocity distribution of different sections of the rectifier and the distribution of turbulent kinetic energy were analyzed.It was found that the mode of rectifier array,the length of the collection section and the contraction angle of the collection section had different influence on the flow state,the rectifying effect and the resistance characteristic of the rectifier,and the performance of the rectifier was further improved through the optimization of the structural parameters.(2)Through the numerical simulation of the length of the converging segment in the rectifier,the size of the contraction angle of the collection section and the different optimization schemes of the gradually expanded jet tube array were simulated numerically,the velocity streamline diagram of the characteristic section in the collection section,the distribution of axial velocity and the uniformity of the velocity distribution of the outlet are analyzed,the resistance characteristics and flow patterns in different schemes are evaluated.Through the study,the characteristic section near the wall side reflux is more obvious,and the radial distribution of the axial velocity fluctuates greatly,the length of the collection section increases,and the internal flow state of the rectifier is improved.When the contraction angle of the collection section is large,the flow state of the collection section and the outlet pipe is too large,and the flow state in the local range has the rapid change flow in the reflux region.Therefore,the flow state is more complex and the energy loss is larger,while the smaller contraction angle will lead to the long length of the collection section,which requires higher site installation conditions.The flow state of the converging jet tube array in the rectifying section also has a certain influence on the flow state in the collection section.The axial velocity distribution,the axial velocity distribution and the outlet uniformity of the rectifier are compared synthetically with the six square and radial arrangement,and the rectifier has better rectifying effect and smaller resistance under the radial arrangement.(3)Based on the above analysis,a set of rectifier structure scheme was optimized.The full transparent rectifier model was made by rapid prototyping technology.The performance test platform of the siphon pipeline was built and a pressure testing system was established for the steady flow.The resistance characteristics of the rectifier were tested and compared with the CFID simulation results.The results show that the numerical calculation was basically in agreement with the experimental results,indicating that the proposed simulation scheme can accurately predict the internal flow characteristics of the rectifier.The resistance characteristic coefficient of the rectifier model is 0.54 when the Reynold number is higher than 50000 in the outflow pipe,and does not change with the flow rate and the change of the inlet and outlet pressure of the whole flow in a certain range.(4)Using the VOF model to simulate the unsteady flow field of the internal rectifier inside the tank,thce influence of the different vacuum degrees and the different submerged depths on the self-absorption characteristic of the rectifier was explored.It was found that the higher the vacuum degree is,the higher the suction height is in the discharge tube under the same submerged depth,the higher the suction height is.The function relationship between the suction height and the vacuum can be expressed by the quadratic polynomial In the same vacuum,the depth of the rectifier is deep and the height of the suction is about low.The submerged depth should be reduced in the engineering application so as to shorten the time required for the start-up phase.