Study On Calculation Method Of Local Head Loss In Thin-Wall Drip Irrigaiton Pipes With Non-Coaxial Emitters

The hydraulic calculation of the drip irrigation system is the basis of engineering design,and the accurate calculation of the local head loss of the drip irrigation drip is an important basis for the hydraulic calculation.Using the practical engineering thin-wall drip irrigation pipes with eleven different non-coaxial emitters as the research objects.the method of indoor experiment as well as dimensional analysis,finite element and CFD numerical simulation technology were adopted in this research.This thesis discussed the effect mechanism of pressure and wall thickness of drip tapes on the shape of cross-section.Analyze the effect mechanism of pressure head,water cross section,emitter structure and other factors on the local head loss of emitter.Find out the relevant factors affecting the local head loss of the drip tapes.Optimal regression formula for the local head loss of drip irrigation and subsurface drip irrigation were obtained in order to provide some scientific basses for our country’s Technical Specifications for Micro-Irrigation Engineering and the hydraulic design theory in subsurface drip irrigation.The main research contents include the following points:(1)Based on 6 commonly used thin-wall drip irrigation pipes with non-coaxial emitters.Through the actual measurement of the relationship between the pressure and the cross-section shape of the drip tapes,it is determined that the drip tapes has a unique emitter structure,the crosssection changes with the pressure.When the pressure value was greater than the pressure threshold,the cross-section was approximately circular.When the pressure value was less than the pressure threshold,the cross-section was approximately non-circular.Drip tapes deformation pressure threshold and drip irrigation with wall thickness showed a positive linear correlation.The pressure threshold becomes bigger as the thickness of drip tapes increased.The equivalent diameter of drip tapes is related to wall thickness and pressure.When the pressure is constant,equivalent diameter becomes bigger with the pressure increased.When the pressure is constant,equivalent diameter becomes smaller with the wall thickness increased.The horizontal and vertical inner diameters of the drip tapes can be calculated by the pressure of the drip tapes,and then the equivalent diameter of the drip tapes under different pressures can be obtained.(2)With 11 kinds of different thin-wall drip irrigation pipes with non-coaxial emitters as the research object,the method on experiment analysis as well as dimensional analysis,finite element and CFD numerical simulation technology were adopted in this research,this thesis analyzed the local head loss of drip tapes.It has been found that the local head loss of drip tapes is mainly related to the length of the emitter,the width of the emitters,the height of the emitters,the geometric shape of the drip tapes,the flow velocity,and the viscosity coefficient of water movement,among which the width of the emitter effected the smallest.Based on the dimensional analysis method,the local head loss structure relational expression of the drip tapes is obtained,and the coefficients of each factor are determined in combination with the measured data,and simplify the calculation model.The model is verified by the test data,and the calculation results of the local head loss model and the simplified model are basically consistent with the measured results.It is recommended to use the simplified model to calculate the local head loss of drip tapes under general working conditions.Based on the finite element method,the local head calculation model is applied.The drip tapes have a special geometric structure.When designing the drip tapes network,we must consider the geometric characteristics of the emitter and the change of the crosssection shape.Otherwise the design results will be inaccurate.(3)With 3 kinds of different thin-wall drip irrigation pipes with non-coaxial emitters as the research object,The geometric deformation law of the subsurface drip tapes was studied by experiments.It was determined that the deformation law of the subsurface drip tapes is different from that of the ground.Under the same pressure and wall thickness,the cross-section shape of the subsurface drip tapes is relatively flatter than that of the drip tapes,and lower equivalent diameter.The ratio of the horizontal inner diameter to the vertical inner diameter of the drip tapes is inversely proportional to the wall thickness and buried depth of the drip tapes.The equivalent diameter of the drip tapes can be determined by the internal working pressure and buried depth of the subsurface drip tapes.(4)Based on the test data of hydrodynamic tests,the law of local water head loss in subsurface drip tapes is studied through CFD numerical simulation.This thesis identified the local head loss factors for subsurface drip tapes.In addition to the length of the emitter,the width of the emitter,the height of the emitter,the geometry of the cross-section,the velocity,and the viscosity coefficient of the water flow,the buried depth has an effect on the drip irrigation.The impact of local head loss is also greater.When the working pressure and buried depth are determined,the fitting formula can be directly used to calculate the local head loss of the subsurface drip tapes.