梯形渠道分流量及其影响因素初探

Diversion flow and its influencing factors in trapezoidal channels

【目的】研究梯形主渠分水口水流形态,分析分水口附近水面变化规律以及分水口水头损失,建立矩形支渠分流量公式,为灌区量水技术的精确化提供支持。【方法】对灌区广泛应用的梯形渠道90°分水口进行分流试验研究,采用分流模型试验设置了5种梯形主渠来流量Q1,每种Q1下又设置5种分流比,共进行25组试验,通过9个控制断面的水深变化分析其水面线变化,规律以及矩形支渠分流量系数(m)与断面Ⅰ傅汝德数(Fr1)的关系;根据矩形支渠分流量Q2与主渠水深和傅汝德数的相关性,建立Q2的计算公式,并对上游傅汝德数和分水口水头损失进行了探讨。【结果】当Q1为26.40和33.17 L/s时,5种分流比下梯形渠道水深的变化规律基本一致,即水深在分水口附近变化很大,水位在分水口口门处有所下降,接近分水口下唇时略有壅水,最大相对壅水高度为上游水深的0.18倍。在同一Q1下,Fr1与m之间呈较为明显的负相关关系。随着分流比的增大,相对水头损失减小,最大相对水头损失为26%;当分流比大于0.6时,相对水头损失保持在较低水平,有利于支渠引水。【结论】最终建立的Q2与水位关系式的决定系数大于0.9,操作简便。梯形渠道90°分水口的分流比控制在0.6左右时相对水头损失最小,该分流比为利用分水口实现流量一体化测控提供了参考。

【Objective】This study explored the flow pattern of trapezoidal main channel bifurcation,analyzed the change of water surface and head loss of the bifurcation and established diversion flow equations of the rectangular branch channel to provide references for accurate water measurement technology in irrigation area.【Method】This study designed a 90°bifurcation in trapezoidal channel.Experiments were conducted under five different trapezoidal main channel flow discharges(Q1)and five different discharge ratios,for a total of 25 sets of conditions.The change of water surface and the relationship between discharge coefficient of the rectangular branch channel(m)and Froude number of the sectionⅠ(Fr1)were analyzed through the water depth at 9 sections.Equations for calculating the discharge of the rectangular branch channel(Q2)were established based on the correlation between water depth and Froude number of the trapezoidal main channel.The Froude number of the trapezoidal main channel and head loss at the bifurcation were also discussed.【Result】When Q1 were 26.40 and 33.17 L/s,the variations of water depth were similar in the trapezoidal channel under 5 different discharge ratios.Water depth changed at a wide range at the bifurcation.The water surface elevation decreased at the bifurcation,but slightly congestion water happened near the lower lip of the bifurcation.Maximum relative congestion water was 0.18 times of upstream water depth.There was a negative correlation between Fr1 and m at same Q1.The relative head loss became smaller with increasing discharge ratio and the maximum relative head loss was 26%.The relative head loss decreased a little when discharge ratio was greater than 0.6,which was beneficial to water diversion.【Conclusion】The equation between Q2 and water depth of the trapezoidal main channel was obtained with R-square greater than 0.9.This equation was easy to operate.The trapezoidal channel 90°bifurcation had a minimum relative head loss when the discharge ratio was controlled to about 0.6.This study provides reference for integration measurement and automated control of water discharge using trapezoidal channel bifurcations.