| In drip irrigation system,the uniformity of irrigation as an important index of design directly determines the merit of drip irrigation system,however,the current design specification mainly focuses on above-ground drip irrigation system,the current underground drip irrigation uniformity change law is still unclear.And there is no effective measurement means for the drip head flow rate in the field underground test,and the calculation method of local head loss of buried pipes is not clear yet,which leads to the lack of relevant test and hydraulic calculation methods.Therefore,in this paper,we propose the calculation method of local head loss of underground drip irrigation pipeline through indoor test combined with CFD numerical simulation,and then measure the actual irrigation uniformity in the field by ultrasonic feedback principle.The main conclusions are as follows.The main conclusions are as follows:1)Using three different sizes of internal patch type drip irrigation belt as the research object,the pressure flow relationship is determined by above ground drip irrigation test,and how the working pressure and vertical soil pressure affect the shape of drip irrigation belt over water section is analyzed by underground drip irrigation test,and the empirical formula for calculating the horizontal and vertical diameter of drip irrigation pipe in underground drip irrigation according to the working pressure and soil pressure is proposed,and the accuracy of the formula is verified by comparing with the measured data,and the results show that the equivalent diameter is positively related to the working pressure and negatively related to the soil pressure.2)Based on the indoor study of inlaid patch type drip irrigation belt combined with CFD numerical simulation,3 sets of drip head size,3 sets of wall thickness,3 sets of burial depth and 7 sets of working pressure,a total of 189 sets of simulations are set,and the influence mechanism is analyzed with the drip head length,drip head height,drip head width,equivalent diameter and water flow velocity in the pipe as the research objects.The results show that the local head loss of inlay drip irrigation tape is positively correlated with the length,width and height of the drip head and the flow rate in the tube,and negatively correlated with the equivalent diameter,which provides a new calculation method to determine the local head loss of inlay drip irrigation tape in underground drip irrigation.3)Using 60 m-long inlaid patch drip irrigation tape with different rated flow rates as the research object,above-ground drip irrigation and in-field subsurface drip irrigation tests were conducted to measure the drip head flow rate,total flow rate and total head loss along the line,and analyze the drip head flow rate and uniformity under the influence of spatial variability caused by different saturated hydraulic conductivity of soil in subsurface drip irrigation by four evaluation indexes,q,q_v,Cu,Eu.The variation law of uniformity was analyzed by four evaluation indexes:qv,Cu and Eu.For drip irrigation tapes with rated flow rate of 4.0 L/h and 2.7 L/h,the total head loss increases,the total flow rate and uniformity decreases,and the fluctuation of drip head flow rate becomes larger after buried under the influence of soil load and spatial variability.For drip irrigation belt with rated flow rate of 1.4 L/h,the total head loss decreases,the total flow rate and uniformity increases,and the fluctuation of drip head flow rate becomes smaller,so the laying length can be increased appropriately in underground drip irrigation.4)Based on the indoor test and field test,the hydraulic calculation model of subsurface drip irrigation system is proposed based on the finite element principle.The model can accurately calculate the head loss,local head loss and uniformity of subsurface drip irrigation by the factors of drip irrigation belt wall thickness,burial depth,drip head spacing,drip head size,working pressure and soil spatial variability. |
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