Three Dimensional Numerical Simulation Of Transient Flow In Water Pipeline

Pipeline leakage detection has always been a difficult aspect in the pipeline operation process.With the continuous development and update of technical means,new methods have been proposed and applied,and the old methods have been improved.In the traditional study of transient flow,one-dimensional calculation methods such as characteristic line method are often used to calculate the pipeline pressure.Such methods can not describe the physical changes of each point in the flow field in detail,but also ignore the fluid structure coupling effect between the pipeline wall and the working medium,which results in the limitation of the transient method in the leakage location of long-distance pipeline.The main research focus of this paper is to solve the transient process in the pipeline by means of three-dimensional numerical simulation,analyze the detailed flow field and flow characteristics,and analyze the fluid structure coupling effect between the pipeline wall and the working medium,so as to realize the application and improvement of the pipeline leakage transient flow detection method.The specific research contents are as follows:(1)Simplify the physical characteristics of simple pipes with different structures and carry out the numerical simulation calculation of simple fluid,compare the internal flow field information of pipes(leakage pipes and normal pipes without leakage)under the same water head,get the relationship between the leakage position and the leakage amount,and then add the dynamic boundary condition(fast linear semi closed valve)to the pipe outlet to get the different structure pipe pairs The response form of transient flow.(2)The influence of the pipe wall and the pipe form on the propagation characteristics of the water hammer wave is simulated by the fluid structure coupling method.The influence of the vibration strain of the pipe on the propagation of the water hammer wave is analyzed.(3)From the propagation characteristics of the water hammer wave front at the elbow and the periodic characteristics of the pressure change at the same length of the elbow and straightpipe outlet,it is verified that the elbow can reduce the propagation period of the water hammer wave in the pipeline.(4)The linear filling effect of the pipeline is explained and analyzed by comparing the simulation results of the transient flow in the pipe with simple fluid and fluid solid coupling.It is found that the pressure of the first phase water hammer is less affected by the location of the leakage.The closer the location of the leakage is to the location of the excitation,the faster the attenuation of the water hammer wave is.When the water hammer wave propagates in the actual pipeline,the wave speed and strength will decrease.This conclusion is verified by numerical simulation.After considering the fluid structure coupling,the line filling effect is weakened,but the essential reason is still the decrease of wave velocity,and the expansion strain and large swing caused by water hammer.The difference of the pipeline form and whether there is leakage or not will change the propagation state of water hammer wave in the pipeline,both of which are the main reasons for the change of water hammer wave shape.According to the characteristics of pressure wave propagation under different pipeline forms and different leakage positions,it is concluded that the location of leakage point can be realized by the pressure distortion position in the first phase of pressure change at the end of pipeline.All in all,the transient method of pipeline leakage location needs to add reasonable incentives to be able to locate the leakage safely and effectively on the basis of not damaging the pipeline.After that,the leakage judgment and location can be carried out according to the characteristics of the pressure change rule on the characteristic section at the end of the pipeline.The water hammer wave velocity at the elbow of the pipeline with elbow is greater than that at the straight pipe section,resulting in the water hammer wave propagation period less than that of the straight pipe with equal length The distance from the leakage point to the end of the pipeline is slightly longer than the actual value.