Numerical Simulation And Experimental Study On Exhaust Performance Of Air Inbreathe-release Valve In Large-scale Irrigation Pipe Networks

With the rapid development of our country’s economy,people’s demand for water resources was increasing and the contradiction between water resources and supply was increasing.It was an inevitable trend for the development of agricultural modernization to vigorously promote the scale of irrigation pipe network to reduce the unnecessary loss in the process of agricultural water use.However,due to the characteristics of large-scale irrigation pipe networks,such as long irrigation distance and large elevation change of pipeline,the air was easy to accumulate in the pipeline,and the burst phenomenon caused by poor exhaust was serious.The air inbreathe-release valve was the most common safety control equipment in the irrigation project.But it was difficult to exhaust continuously under the condition of gas and liquid interval.Therefore,to develop a new air inbreathe-release valve which can exhaust continuously under any condition,with safety,reliability,wide range of application and strong exhaust performance,and to prove up its exhaust performance and the flow of gas inside it during the exhaust process was of great practical significance to solve the safety problem of large-scale irrigation pipe networks.Based on the above understanding,the main contents and results of this study were as follows:(1)The paper introduced the types,working principles and structural features of common air inbreathe-release valves,and summarized the advantages and disadvantages of various air inbreathe-release valves,which provided a basis for the selection of air inbreathe-release valves in practical engineering;(2)On the basis of sufficient investigation,the paper pointed out the problem that the existing air inbreathe-release valves could not exhaust continuously under the condition of gas and liquid interval.By using on the principle of pressure distribution,the two new air inbreathe-release valves of pipeline irrigation are designed,namely "single chamber integrated full pressure air inbreathe-release valve" and "double chambers external connection full pressure air inbreathe-release valve".Then through the test of the principle prototype of guide valve,the possibility of the new air inbreathe-release valve driven by pressure mechanism to realize the continuous exhaust under the condition of gas and liquid interval was verified.(3)As an example of DN50 size of "double chambers external connection full pressure air inbreathe-release valve",by using 3D modeling software GAMBIT and fluid calculation software ANSYS CFX,the paper carried out the numerical simulation of the flow field in the main valve chamber of air inbreathe-release valves under different valve opening degrees;by extracting the information of the important shear surfaces in inner region,such as pressure distribution cloud map,velocity distribution cloud map,flow line map and so on,the paper showed the direction of air flow in the valve body directly,and described the distribution of pressure and flow velocity;by using comparative analysis of the important shear surface inside the main valve cavity under different working conditions,the paper proved up the effects of valve opening degree and inlet and outlet pressure difference on internal flow in the main valve cavity and valve exhaust volume.(4)By using physical test,the paper studied on the exhaust volume of the air inbreathe-release valve under the valve opening degree of 0.4cm,0.8cm and 1.2cm and fittings test results under the same opening degree with different working conditions,then established relation function between exhaust volume and pressure difference of different kinds of valve opening degrees;and the paper used the fitting function to calculate the exhaust volume under the pressure difference conditions of numerical simulation,then compared with the numerical simulation results,the deviation was between 0.08～6.43%the feasibility of the numerical simulation method and the correctness of the simulation model were verified.(5)The physical test measures the maximum exhaust volume of new DN50 airinbreathe-release valve is 852.95m/h and 1314.45m3/h when the exhaust pressure difference is 0.035MPa and 0.07MPa.The exhaust volume of new air inbreathe-release valves exceed 27.31%and 21.71%which specified in the related industry specifications(670m3/h and 1080m3/h).Its exhaust performance meets the design requirements of the air inbreathe-release valve.