Experimental And Numerical Study On Two Phase Flow In Horizontal And Inclined Self-Pressure Water Pipelines

Agricultural water pipeline is an important part of efficient water transmission and distribution system,and because the pipelines are buried underground,it is difficult to repair.For the whole self-pressure drip irrigation system,although there is no air brought into the pipeline during the operation of the pump,such as vacuum intake caused by rapid pump stop,negative pressure gas release in the impeller area,there are still other forms of air entry,such as dissolved in water.The separation of gas in water,the gas entering the pipeline from the pipeline connection due to poor sealing when the pipeline is under negative pressure,etc.When the gas exists and is not discharged in time,it will lead to the change of the flow pattern in the pipeline.The light one will cause the gas phase to slow down the water delivery speed,cause the vibration of the pressure in the pipeline,increase the water resistance and so on.The heavy one will cause the pipeline to burst and interrupt the water supply.Therefore,it is very important to study the two-phase movement in the pipeline in the process of self-pressure water delivery,which can reduce the occurrence of pipe burst,water leakage and other accidents.In this paper,the gas-liquid two-phase flow process in horizontal and 15° downward inclined pipeline is studied by using the method of indoor pipeline test and numerical simulation combined with the previous two-phase flow theory:(1)The horizontal and 15° downdip pipeline test platform was built to form a complete self-pressure backwater system,and the gas and liquid volume were adjusted to change within a certain range.The twophase flow diagram and pressure data in the pipeline were obtained by photographing and sensor acquisition equipment.Finally,the typical flow pattern image and pressure fluctuation curve of the test section of 40 mm and 60 mm diameter pipeline system were obtained.The conclusions are as follows: under horizontal conditions,with the decrease of liquid flow,the typical flow patterns obtained include bubble flow,plug flow and stratified flow;with the increase of gas flow,the number of bubbles in bubble flow pattern increases and the vertical distribution is more uniform,and the increase of gas plug length in plug flow pattern changes from periodic short gas plug to long gas plug;the increase of gas and liquid flow will aggravate the internal pressure of pipeline Force fluctuations.Under the inclined condition,with the decrease of liquid volume,the typical flow patterns are obtained,including bubble flow,intermittent flow and stratified flow;with the increase of gas volume,due to the influence of gas accumulation on the downstream liquid velocity,the flow pattern will still change;with the increase of liquid volume,the pressure fluctuation first increases and then decreases,and increases with the increase of gas volume.(2)In order to obtain the influence of pipe diameter on the transformation of flow pattern,threedimensional numerical models of horizontal and 15° downdip pipes were established and imported into fluent to simulate the two-phase flow.Keep the gas phase conversion speed unchanged,and complete the simulation process under 15 working conditions with the liquid phase conversion speed of 5m/s,4 m/s,3m/s and the pipe diameter of 160 mm,120mm,80 mm,60mm,40 mm in horizontal condition;complete the simulation process under 15 working conditions with the liquid phase conversion speed of 3m/s,2m/s,1.5m/s,1m/s,0.5m/s and the pipe diameter of 120 mm,60mm,40 mm in downward inclined pipeline.The data of pressure and velocity were obtained.The conclusions are as follows: under horizontal condition,with the increase of pipe size,the starting point of bubble plug flow transition moves to a higher liquid phase conversion velocity;with the decrease of pipe diameter,the peak pressure and the maximum pressure difference first decrease and then slightly increase,and the pressure fluctuation of 60 mm pipe diameter is the smallest;the position of maximum velocity remains unchanged,which is the high density in the upper part of the pipe In the bubble zone,the average liquid velocity decreases sharply to the upper wall of the pipe.Under the condition of downdip,with the increase of pipe diameter,the transition boundary between intermittent flow and stratified flow shifts to the direction of larger liquid phase converted velocity,the transition boundary between bubbly flow and intermittent flow tends to the direction of smaller liquid phase converted velocity,and the region of intermittent flow gradually decreases;the pressure fluctuation has little effect with the change of pipe diameter;the influence of laminar flow on the average velocity of pipe section is obviously greater than that of bubbly flow.At this time,the position of the maximum flow velocity of the pipeline shifts downward.The above studies further improve the level and 15 ° The flow process and flow pattern transformation boundary of gas-liquid two-phase flow in downdip pipeline with different pipe diameters have certain reference value for the normal operation of actual water conveyance project.