2种土壤地下滴灌滴头流量变化规律及对入渗空腔的响应

Variation law of subsurface drip irrigation emitter flow rate and response to infiltration cavity in two types of soils

为研究入渗空腔对地下滴灌滴头流量和土水势的影响规律,通过土箱试验和数值模拟相结合的方法,对比分析了黏土和壤质砂土2种土壤灌水过程中土壤正压及滴头流量的变化规律,反演了滴头出口处空腔半径,并建立了黏土中空腔半径的计算模型.研究结果表明:相同条件下,壤质砂土中的滴头流量大于黏土中的,但变化幅度小于黏土中的;壤质砂土中土壤正压随时间变化呈上升趋势,黏土中土壤正压随时间变化呈下降趋势,受空腔影响,滴头流量与土壤正压随时间的变化趋势不存在必然关系.模拟中,壤质砂土入渗空腔半径可选择较小值或认为与滴头出口半径相同.黏土中空腔半径随滴头额定流量和容重增大而增大.相对于选用固定值,研究得到的空腔半径可以提高现有计算公式在求解滴头流量和土壤正压的精度,拟合的空腔半径经验模型可以应用于地下滴灌水力设计,同时为土壤水分入渗数值模拟的边界条件设置提供依据.

The influence of infiltration cavity on the emitter flow rate and soil water potential of subsurface drip irrigation was studied by using a soil tank experiment and numerical simulations.The variation of soil back pressure and emitter flow rate during the irrigation process in clay and loamy sandy soil was compared.The cavity radius at the outlet of the emitter was inverted,and a calculation model for the cavity radius in clay was established.The results show that under the same conditions,the emitter flow rate in loamy sandy soil is larger than that of clay,but the variation amplitude is smaller than that of clay.The back pressure of soil in loamy sandy soil increases with time,while the soil back pressure in clay decreases with time.There is no inevitable relationship between the variation of emitter flow rate and the soil back pressure due to the influence of cavity.In the simulation,the radius of the infiltration cavity of loamy sandy soil can be taken as a small value or be considered to be the same as the emitter outlet radius.The radius of the cavity in clay increases with the increase of emitter nominal flow rate and soil bulk density.Compared with the constant value,the cavity radius obtained in this study can improve the accuracy of the current formulas in solving the emitter flow rate and soil back pressure.The fitted empirical model of cavity radius can be used for the hydraulic design of subsurface drip irrigation and provide a basis for the setting of boundary conditions for the numerical simulation of soil water infiltration.