Numerical Investigation Of Water Hammer In Pressure Pipes Based On Flow-3D

In the actual water delivery system,when the pump or the valve is suddenly closed,it will cause dramatic change of flow and pressure in pipeline,which can cause damage to the pipeline.The method of characteristics is widely used to get water hammer pressure due to its accuracy of calculation and tractable boundary conditions.It is necessary to analyze water hammer pressure in pipelines,which can predict the type of water hammer and pressure changes law to make sure the possible maximum and minimum pressure values.So the protective measures can be taken to reduce the pipeline damage caused by water hammer.The method of characteristics is widely used to get water hammer pressure due to its accuracy of calculation and tractable boundary conditions.However,this method only gets the one dimensional pressure fluctuation along the pipeline instead of the overall flow parameters in pipeline.Therefore,the software of Flow-3D is employed in this paper to simulate the water hammer phenomenon in pipeline.It is widely used in hydraulic processes,which adopts the real volume method to establish calculation model.Thus,it can accurately capture the change of the liquid fre e face and get the two-dimensional pressure condition and steam hole.The main work of this paper is as following:Combining the study of transient flow with free surface by Flow-3D software and theory of water hammer pressure in pipelines,the calculation model and boundary conditions are established,and then transient flow model by method of characteristics is established at the same time;The model with the method of characteristics and Flow-3D software are used to simulate the water hammer pressure in pipelines under the ideal condition(no frictional resistance in the pipeline)and to study the effect of number of grid on simulated result,the size of the time step,and the type of the turbulence model.The optimal model is selected to solve the pressure fluctuations at the valve and middle of pipe.Both the method of characteristics and Flow-3D are employed to calculate the pressure fluctuations at the valve and middle of the pipeline when the valve at the end of the pipeline is closed suddenly.The results from two methods agree well with each other,which show that Flow-3D can be used to simulate the water hammer pressure in pipelines.Compared with the experimental data,the maximum of relative error between simulated pressure by Flow-3D and experimental pressure is less than 6% and that between simulated pressure by method of characteristics and experimental pressure is more than 10%.It means that the Flow-3D can get more accurate pressure data than method of characteristics compared with experimental data.The formation reason and flow characteristics of the steam hole during the hydraulic transient of the water hammer are described in this paper.The cavity collapsing model with the method of characteristics and Flow-3D software are established to simulate the pressure fluctuation and change of volume fraction of steam cavity in three different flow rates.Compared with experimental data in reference,it shows that simulation results by Flow-3D software are closer to the experimental results.There is no false pressure pulse in the simulation results from Flow-3D.It can well simulate the pressure attenuation since the steam hole collapses.And it can capture the evolution process and position of the steam cavity in the water hammer of cavities collapsing.