Study On Hydraulic And Infiltration Characteristics Of New Insertion Subsurface Emitter

Subsurface drip irrigation is an efficient water-saving irrigation technology and an important measure to solve the shortage of agricultural water resources.Due to the common problems in practical application of subsurface drip irrigation emitters,such as difficult to find,difficult to maintain and poor flexibility,Therefore,under the support of the National Natural Science Foundation of China(U1803112),this paper develops a new type of insertion subsurface emitter based on the theory and experiment,and studies the hydraulic characteristics of the emitters,such as the pressure flow relationship,the uniformity of irrigation and the infiltration characteristics of the wet body through the indoor simulation test,so as to provide theoretical basis for structure optimization and application development.The main research contents and achievements are as follows:(1)Based on the design principle of subsurface drip irrigation products and the results of indoor simulation test on the outflow effect of spiral flow channel,a new type of insertion subsurface emitter was developed which can achieve the goal of root zone irrigation.(2)The irrigation quality of the new insertion subsurface emitters under different outflow conditions meets the requirements of the specification.Under the condition of free outflow,the uniformity of irrigation is more than 92.5%;under the condition of underground outflow,the uniformity of soil moisture is more than 77%;the uniformity of water distribution is more than 64%.The calculated values of uniformity indexes meet the requirements of technical specifications.Under the single factor test,the influence of water supply pressure on irrigation uniformity,soil moisture uniformity and water distribution uniformity was small.When the working pressure is constant,the shorter the distance between the emitters,the higher the uniformity of irrigation,the shallower the depth of the emitters,and the better the quality of irrigation.(3)The mathematical model between the discharge and the water supply pressure of the new insertion subsurface emitters under different discharge conditions is established,and its form power function.Under different outflow conditions,the flow coefficient and flow index of the model are quite different.The flow coefficient of the underground outflow is 0.219 and the flow index is0.852.Compared with the average flow coefficient and the average flow index of the free outflow,the flow coefficient of the buried outflow is decreased about 46%,the flow index is increased about 22%,and the outflow of the emitter is significantly lower than that of the free outflow.By introducing the reduction coefficient of flow and the reduction index of flow,the pressure-flow relations of the irrigator under different discharge conditions are unified.(4)The critical condition of the new insertion emitters without backflow phenomenon(the water flows upward along the shell of the emitters to the surface)was explored(when the design working pressure,the depth of the emitters≥20cm or the water supply pressure≤14m under the critical depth).Under the design condition,a mathematical model(R~2>0.98)was established for the wetting front migration distance and infiltration time under different emitter buried depth,and a fitting formula between the wetting front migration distance and the water supply pressure and infiltration time was constructed.The average error range was 0.15cm～1.14cm,the average relative error range was 2.13%～13.45%,and the root mean square error range was0.18cm～1.82cm。(5)The moisture distribution law of the wet body of a new insertion subsurface emitter is revealed.The water content of the soil near the drip hole of the emitter(22%～27%)is higher,and the soil water content gradually decreases with the increase of the wet body radius.Most of the moisture content of the wet body is greater than 80%of the field water capacity under all working conditions,Which means this kind of emitter can reach the moisture content required by the crop plan wet layer in a short irrigation time.(6)The influences of infiltration time,emitter buried depth and water supply pressure on the cumulative infiltration are studied.The mathematical model(R~2>0.99)between infiltration time(t),water supply pressure(H)and cumulative infiltration(I)is obtained by regression analysis using the Macquarie method+general global optimization algorithm The average error between the simulation value and the simulation value is 0.0336l,the average relative error is 5.9029%and the root mean square error is 0.0453l.The research results can provide theoretical reference for the structural optimization design and field application of the new insertion subsurface emitters.