The Study Of Local Head Loss In Different Types Of Emitter Laterals

Accurate calculation of local head loss of drip irrigation pipe is the basis of the uniformity in drip irrigation design, and the irrigation uniformity is an important index in the evaluation of system designing reasonableness. Using the practical engineering trickle laterals with three different emitters as the research objects, the method of indoor experiment as well as dimensional analysis and CFD numerical simulation technology were adopted in this research.This thesis discussed the effect mechanism of introduced emitters on the pressure head of trickle laterals and clarified the mechanism of action of related factors on the local head loss in trickle laterals by analyzing the variation of emitter flow rate and pressure.Optimal regression formula for the calculation of different kinds of local head loss were obtained in order to provide some scientific basses for the hydraulic design theory in drip irrigation. The main research contents include the following points:(1) Based on 4 commonly used drip irrigation pipes with inserted emitters, The method of in indoor experiment as well as dimensional analysis and CFD numerical simulation were used, this thesis analyzed the influence of the local head loss caused by the shape of emitters and Reynolds number in both laminar flow and turbulent flow conditions. The results show that numerical simulation of the local head loss agreed highly to the tests. In both conditions,the local head loss coefficient decreased when the Reynolds number jumped and the coefficient increased with drop of cross-sectional area ratio. This thesis also found the return of flow in head and tail of the pipe was the main reason for the loss of head pressure.(2) Based on 6 groups of drop pipes with different drop spacing, the effect of the local resistance of the head was analyzed by using CFD numerical simulation. The simulation results were basically in agreement with the experimental results. The CFD numerical simulation could help to observe the flow disturbance state near the head and revealed the mechanism of the impact of the drop head. The influence coefficient of local resistance to the drop head was mainly affected by the drop head spacing and the Reynolds number barely affected anything. The influence coefficient of local resistance to drop head decreased with the decrease of drop head spacing. The variation of the perturbation range and the velocity distribution was the main reason of the adjacent influence of the drop head local resistance. In drip irrigation design, when the drop head spacing was less than 0.5 m, the adjacent influenceof the drop head local resistance should be considered, and the adjacent influence coefficient was 0.85 ~ 1.(3) The simulation of lateral local head loss was made through dimensional analysis in12 kinds of drip irrigation pipes. When the deviation of the head diameter was small, the local head loss was slightly smaller than that of the experimental data, and when the deviation of the head diameter was relatively large, the local head loss was slightly less than that of the experimental data. The deviation of the inner diameter of drip tube was the main reason causing the error between the measured results and simulation results. Numerical simulation was able to analyze the coefficient of each factor. The capillary diameter, head diameter, drop head length, flow velocity and flow viscous lag coefficient all affected the local head loss in mosaic column type capillary, and the impact of the drop head’s diameter was the most obvious. The influence of temperature on local head loss was negligible when the requirement for calculation is not precise.(4) With six kinds of different thickness of drip irrigation belt as the research object,through measuring drip irrigation section shape of the belt affected by the pressure force, this thesis identified the local head loss factors for embedded dropper. The shape of the cross section of the drip irrigation belt changed along with the pressure.When the pressure was greater than the critical pressure, the water section was approximately circular. When the pressure value was less than the critical pressure, the water cross section was approximately oval. Drip irrigation belt deformation critical pressure and drip irrigation with wall thickness showed a linear correlation. The deformation critical pressure becalmed bigger as the thickness of drip pipe growled. The local head loss was related to the section shape, the length of drip head, head width and drip head thickness, among which the section shape affected the most. The fitting formula could be used to calculate the local head loss when the drip irrigation belt section was circular, and it was necessary to determine the flat degree of drip irrigation.(5) Based on the above research, using the method of division and step by step calculation of local head loss and total head loss and frictional head loss ratio in the emitter lateral, this thesis found the local head loss closely related to the distance between heads and emitter discharge. The head loss of the drop head increased with the decrease of the drop head distance and the increase of head flow rate and the impact of drop head spacing was particularly evident. For the same emitter spacing, flow rate and diameter of capillary, insert type dripping head and mosaic column emitter type drip local head loss was relatively large,inlaid patch type drip head local head loss was relatively small. The calculated expression of head loss expand coefficients of two different drop laterals have been obtained. And the headloss expand coefficient is associated with the emitter spacing as well as the emitter flow rate,among which the influence of emitter spacing is more significant. Under common condition of drip irrigation, the head loss expand coefficients range for the insert emitter type, mosaic column emitter type and inlaid patch emitter type are 1.39~2.49, 1.18~2.89 and 1.1~1.2,repectively. For three different types of drop head, under the state of laminar flow in lateral head loss values were relatively small. Without precise calculation the head loss could be ignored in laminar lateral head loss.