Hydraulic Performances And Jet Breakup Characteristics Of Low Pressure Sprinkler Based On Special Shaped Nozzles

Spray irrigation system is mainly composed of water source projects,pumps,power equipment,water pipe systems and sprinklers.Sprinklers are the key equipment and decide the irrigation performance.And sprinklers' performance depends on factors like working pressures or structures.So improving sprinkler hydraulic performance can be done by various ways.Special shaped nozzles is one of them.As a non-circular nozzle,the special shaped nozzles can achieve uniform spray at low pressures,and has the advantages of improving the range and atomization condition of the sprinkler.Therefore,it is significant to study the performance of low-pressure energy-saving sprinklers based on special nozzles and know well the characteristics of the jet breakage.In this paper,the hydraulic performance of two kinds of non-circular nozzles and circular nozzles are studied.The effect of different pressures and nozzle shapes on the hydraulic performance is analyzed.The shape of the jet morphology is studied by high speed photography and the change law of the jet breakage is analyzed.The VOF and the large eddy model(LES)are used to simulate the circular jet flow field,and the relevant characteristic parameters of the circular turbulent jet are verified.The research contents and results are shown below:(1)According to principle of the same flow rate,parameters and shapes of the nozzles are designed.Hydraulic performance test is carried out by selecting the impact sprinkler PY115.The influences of working pressure,nozzle shape and inlet cone angles on performance are studied.The results show that the flow coefficient is related to the shape of the nozzle.The coefficient of the circular nozzle is the largest while the square's is the second and the normal triangle's is the smallest.The flow coefficient also affected by inlet cone angle and the flow coefficient increases as inlet core angle increases.As the working pressure increases,the flow rate and range of the nozzle increase correspondingly,but range stops growing up after the pressure increases to a certain value.The optimum combination uniformity coefficient of the special nozzle under 150 k Pa is greater than that of the circular nozzle at 200 k Pa.(2)Build the experimental system of jet breaking characteristic research,and use high-speed photography technology to analyze the shape of the jet and the amplitude surface wave of the initial segment of the jet.The results show that with the increase of working pressure,the jet turbulence intensifies and the breakage of the jet is more intense.Different inlet cone angles with the same nozzle shape cause the change of the jet breakage.From the triangle to the square to the round,the shape of the nozzle is closer to the circular nozzle,the better the fluidic agglomerate is,the longer the breaking length is.Under different working pressure,the numbers of the finger structure,the structure of the liquid band and of the droplets of the satellite are different,and the location of their appearance and disappearance is random.With the increase of the cone angle of the inlet,the number of finger structure,the liquid band structure and satellite droplets increase.(3)Studying the development of turbulent jet,initial stage,transition section and main segment included.By combining VOF and LES,the numerical simulation of the jet flow field of the circular nozzle is carried out,and the liquid volume distribution cloud pattern is obtained.The simulation explains the spatio-temporal evolution of the jet structure,the production and fragmentation of the liquid zone and the entrainment phenomenon.At the same time,the velocity distribution of the different sections is measured.It is found that the velocity at the central axis is the largest,and the speed away from the axis is decreasing.Changing the inlet cone angle of the nozzle in simulation to study the external flow field of the initial section of the jet.It is found that the amplitude of the surface wave increases and breakup degree becomes higher with the increase of the cone angle.And a large number of liquid belts and tiny droplets show at 55 degrees.There are interconnected positive and negative pressures on the surface of the jet.This feature gets obvious when inlet core angle increases.