地下滴灌中毛管水力计算的数学模型与试验

Experiment and mathematical model on hydraulic calculation of laterals in subsurface drip irrigation

为了研究地下滴灌毛管水力特性与水力计算方法,用较短毛管并通过毛管末端泄流的方式,在室内利用地下滴灌毛管水力要素试验测试系统,分别测试了2种滴灌管在轻黏土中毛管上每个滴头的流量和毛管首末两端的压力水头.结果表明:在灌水持续2 min之后,地下滴灌毛管上各滴头流量均趋于恒定值;在稳定的压力水头差下,滴头流量沿程依次减少.根据毛管沿程压力变化规律,结合考虑土壤质地、土壤体积质量和初始含水率的地下滴灌滴头流量计算公式,提出了毛管水力计算数学模型.利用该模型计算的滴头流量值与其实测值之间的相对误差在1.0%左右;并计算出考虑毛管局部水头损失的加大系数约为1.20.将该模型推广应用于一般情况下的地下滴灌毛管水力计算,可求解均匀坡、均质土、均匀管径与滴头等间距时的地下滴灌毛管水力特征值.

In order to study hydraulic characteristics and hydraulic calculation method of SDI lateral, emitter discharge and lateral pressure head of two drip irrigation pipes in light clay were measured respectively by using shorter lateral with end flow and the laboratory test system of SDI lateral. Experiment results showed that discharge of every emitter was ahnost invariable with time after 2 min irrigating. Emitter discharges reduce in turn along SDI lateral under a certain pressure difference. According to variation of pressure head along lateral, mathematical model of hydraulic calculation in SDI lateral was built based on the empirical formula for calculating SDI emitter discharge, which considered soil texture, soil mass density and initial soil moisture. The relative rotor between model computing results and measuring results was about 1.0%. The increasing coefficient considering local head loss of SDI lateral was about 1.20. The model can be applied to solving hydraulic characteristic values of SDI lateral under uniformity slope, homogeneous soil, and unchanged diameter and spacing of laterals.