The Study On Local Hydraulic Transient Progress And Transient Flow Simulation In Long Distance Water Supply Pipelines

The elevations of long distance water supply pipeline go ups and downs along the way, influenced by the elevation. Therefore there are vent usually set in the local high point. Under normal operating conditions, the entire pipeline system is pressurized water delivery. When the pipeline system is filled with water or performs flow regulation, the downstream portion of the pipe may become non-pressure flow of fluid and the gas in pipe will communicate with the atmosphere. Therefore,there are two states of fluid at this point:free surface flow and pressurized flow. There a water jump may happen in their interchange, resulting in a sudden increase pressure in the partial of the pipeline. This condition of the pipeline system can be known as the combined free surface and pressurized flow system.In steady state combined free surface and pressurized flow system, there were three conditions of fluid in the pipeline: free surface flow, pressurized flow and hydraulic jump. All these types of flow could be modeled by establishing basic equations and calculated for the hydraulic parameters. An internal boundary condition was needed for transient flow numerical simulation by establishing a continuity equation for transition position where the free surface flow turns to the pressurized flow. A valve control equation was also needed in the downstream of the pipeline for calculating the hydraulic transients caused by a sudden movement of the valve. This research would use MATLAB to program and calculate all the numerical methods. There were conclusions as following:In the combined free surface and pressurized flow system,the the dimensionless depth Dh / of free surface flow increased with the flow of pipe and Fr1 increased with the dimensionless depth Dh /.When Dh3.0/ ?, Fr1 would reach the maximum value, the height of hydraulic jump also would reach to a highest point and the hydraulic jump would be the most severe. Because the water cross section after hydraulic jump was limited by pipe diameter, Fr2 is greater than 1 and the flow is still rapids. That is to say the occurrence of hydraulic jump is only associated with fluid velocity change and has nothing to do with the flow regime.In the transient flow simulation, while a sudden closing(opening) of the valve in the downstream happened, the pressure at the valve would increase(decrease)rapidly, resulting as a pressure fluctuation. Due to the friction of the pipeline, the water hammer wave gradually attenuated, then the pressure of valve would increase(decrease) at a fixed rate. In the same operating condition, the pressure produced by water hammer in the combined free surface and pressurized flow system was lower than that in full-pressurized flow. Therefore, ignoring such conditions of practical engineering checking had no effect on the piping design.