Experimental Study And Numerical Simulation On Head Loss Of On-line Emitter In Drip Irrigation Laterals

It is rarely taken interaction effect of local resisitance by on-line emitter intoconsideration in hydraulic design of drip irrigation. In fact people only to use coefficient oflocal resisitance or ratio of friction loss recommend by Technical standard of Micro IrrigationProjection to calculate local head loss that is small or large, far from the exact value. In orderto improve hydraulic design of drip irrigation, the research have chosen tow common on-lineemitters to analysis the law about head loss in drip irrigation lateral and used CFD technologyto study the interation effect of local resisitance by on-line emitter. The research obtained thefollowing conclusions:1) For on-line emitters, the ratio of local head loss over the fictional head loss in dripirrigation lateral hj/hfis greater than those specified in the Technical standard of MicroIrrigation Projection. According to the standard, the local head loss is about (0.1—0.2) of thefrictional head loss, obviously the total head loss will be underestimated by this. the ratio oflocal head loss over the fictional head loss in drip irrigation lateral is correlated to Reynoldsnumber and emitter spacing for different types of emitter. For same type of emitters, hj/hfisinversely proportional to emitter spacing.2) The coefficient of local resisitance is correlated to types of emitter、emitter spacingand Reynolds number. For labyrinth channel emitters the coefficient is higher than0.6;however, for compensating pressure emitters, it is ranged in0.3—0.5. The coefficient of localresisitance increasing with decreasing emitter spacing, and declines with increasing Reynoldsnumber. The larger Reynolds number, the little interaction on coefficient of local resisitance.An empirical formula which considered the effect of emitter types、emitter spacing andReynolds number to coefficient of local resisitance have proposed by regression.3) To use computational fluid dynamics model can simulate the real flow situation in dripirrigation laterals. The flow situation in drip irrigation laterals is complex, emitter types、emitter flow rate and flow velocity in laterals are effect on total head loss. The Low speedwhirlpool zone appeared at the both bottom of emitter, it is easy to cause the sediment orimpurity precipitation and deposition. Emitter inserted and emitter flow can lead to flow ratein lateral redistribution and recombination, that also perturbance streamlines and affect some area, all of them are interaction effect of local resisitance by on-line emitter.4) The turbulence length appeared by emitter inserted is correlated to flow velocity inlaterals、emitter flow rate and area ratio of emitter and lateral.Turbulence length firstincreasing with velocity increasing, then decreasing with velocity increasing, finally it to bestable. When emitter flow rate is equal, turbulence length increasing with area ratio of emitterand lateral increasing.5) Equivalent length first increasing with Reynolds number increasing, then decreasingwith Reynolds number increasing, finally it to be stable. When Reynolds number range from2000to3000(transition flow), the equivalent length reaches maximum value. When area ratioof emitter and lateral and Reynolds number are equal, equivalent length increasing withemitter flow rate increasing.When emitter flow rate is equal and Reynolds number is below10000, equivalent length is inversely proportional to area ratio; when Reynolds number isbeyond10000, equivalent length is direct to area ratio. Use variance and linear analysis to getthe relationshio amog equivalent length of lateral、Reynolds number and area ratio of emitterand lateral. When Reynolds number is small, equivalent length only changes with Reynoldsnumber; and Reynols number increasing, the geometry size of emitter is effect on equivalentlength. The empirical formula have proposed by regression can estimate equivalent length.