臂坡对堰槽组合设施测流影响分析

针对堰槽组合设施在遭遇洪水、水位较高时引发的坡脚掏蚀、岸坡冲刷崩塌等问题，将设施两侧堰顶设置一定坡度，形成向槽内倾斜的臂坡，使水流向设施中部集中，减少对两岸边坡的冲蚀。采用水力性能试验的方法，对3种臂坡(0，1/16和1/8)在12种流量(6~61 L/s)条件下的中垂面水深、弗汝德数沿程变化规律、臂坡对设施泄流能力的影响及流量公式进行研究。结果表明:1)3种臂坡下的堰槽组合设施水深沿程变化相似，随着臂坡的增大，中垂线上游水位壅高增大，两侧堰靠近岸坡一侧的堰上水深减小，明显减少了水流对两岸边坡的冲蚀；2)臂坡对临界流断面位置影响较小，集中出现在排淤量水槽梯形窄段的后半段；同一流量下，堰槽组合设施的流量系数随臂坡的增大而减小；同一臂坡下，堰槽组合设施的流量系数随着流量的增大而减小；3)相对水头较小时，流量系数变化明显，相对水头较大时，流量系数相对稳定，将流量系数分为变动流量系数和稳定流量系数2个区，并分别拟合出不同臂坡条件下的流量计算公式，与实测流量相比，臂坡为0、1/16和1/8时，相对误差绝对值的最大值分别为2.22%、2.37%和2.21%，平均相对误差分别为0.88%、0.95%和1.15%。此外，在流量为11 和21 L/s时，臂坡的增大使得流量公式计算值的相对误差由-2.22%降至-0.44%和由2.35%降至-0.24%。综上，臂坡的存在能够减少水流对两岸边坡的冲蚀，对临界流断面的影响较小，增大臂坡还可有效提高堰槽组合设施在小流量情况下的测量精度。

Influence analysis of crest slope on the flow measurement of weir-flume combination facility

Given the problems of weir-flume combination facilities such as slope foot erosion and bank slope collapse caused by flood, a certain slope is set on the weir top on both sides of the facility to form a crest slope which inclined to the flume, so that the water is concentrated in the middle of the facility and the erosion on both sides of the bank slope reduced. With the hydraulic performance experiment, the mid-vertical water depth, the variation of Froude number, the influence of three crest slopes(0, 1/16 and 1/8)on the discharge capacity of the facility and the flow formula were studied under twelve kinds of discharges(6-61 L/s). The results show that: 1)The water depth of the weir-flume combination facilities with the three crest slopes has similar changes along the flume. With the increase of the crest slope, the water level upstream of the mid-vertical line increased. The water depth on the weir near the bank slope is reduced, which can reduce the erosion of water flow on both sides of the bank slope. 2)The crest slope had little influence on the location of the critical flow section, which mainly occurs in the second half of the trapezoidal section of the drainage flume. Under the same discharge, the discharge coefficient of the combination facility decreased with the increase of crest slope. Under the same crest slope, the discharge coefficient of the facility decreased with the increase in discharge. 3)When the relative hydraulic head was small, the discharge coefficient varied greatly. When the relative hydraulic head was large, the discharge coefficient was stable. The discharge coefficient was divided into two parts: the variable discharge coefficient and the stable discharge coefficient, and the discharge calculation formulas under different crest slope conditions were fitted respectively. Compared with the measured discharge, when the crest slope was 0, 1/16 and 1/8, the maximum absolute value of relative errors was 2. 22%, 2. 37% and 2. 21%, respectively, and the average relative errors were 0. 88%, 0. 95% and 1. 15%, respectively. In addition, when the discharge was 11 L/s and 21 L/s, the increase in crest slope made the relative error of the flow formula decrease from -2. 22% to -0. 44% and from 2. 35% to -0. 24%. Therefore, the existence of the crest slope can reduce the erosion of water flow on both sides of the bank slope and has little impact on the critical flow section. The increase in crest slope also improves the measurement accuracy of weir-flume combination facilities under the small discharge.