量水槽出口宽度对堰槽组合量水设施过流能力的影响

Influence of outlet width of flume on overflow capacity of weir-flume combination facility

【目的】研究量水槽出口宽度对堰槽组合量水设施水力性能及对测流的影响,为扩大堰槽组合量水设施的适用性提供参考。【方法】对3种量水槽出口宽度(b=25,35和45 cm)在不同流量(5~71 L/s)下的35种工况进行水力性能试验,通过中垂面30个测点的水深及垂线平均流速变化,分析出口宽度对设施中垂面水面线和佛汝德数(Fr)沿程变化的影响,明确槽内流和堰槽流的流量阈值;根据流量(Q)与量水槽内测点水深的相关性,分析量水槽出口宽度对流量系数的影响,并建立不同量水槽出口宽度下的流量公式。【结果】3种量水槽出口宽度条件下,中垂面水深和Fr的沿程变化均表现出相似的规律,即中垂面水深在上游段表现稳定,进入量水槽后逐渐下降至出口后的薄水层区域;Fr值在上游段相对平稳,保持在0.1~0.2,进入量水槽后逐渐增大至最大值1.2~1.5,且增大速率沿程变大。上游段的水深和量水槽内的水深均随量水槽出口宽度的增加而减小,出口段、薄水层区域和下游壅水区域的水深受量水槽出口宽度影响不大。上游段至量水槽内部过渡扭面段的Fr值随量水槽出口宽度的增加而增大,量水槽内部梯形窄段的Fr值随着出口宽度的增加而减小。同一量水槽出口宽度下,槽内流的流量系数随流量的增加而增大,堰槽流的流量系数随流量的增加而减小。同一相对作用水头下,槽内流的流量系数随量水槽出口宽度的增加而减小,堰槽流的流量系数随出口宽度的增加而增大。基于建立的3种量水槽出口宽度下的流量公式,得到的流量计算值与实测值的相对误差均在2%以内,使堰槽组合量水设施的适用范围进一步扩大。【结论】量水槽出口宽度对上游和量水槽内的水深有明显影响,出口宽度的增加能够增大堰槽组合量水设施的流量阈值及过流能力,并使临界水深的断面位置向下游推移。

【Objective】To provide reference for expanding the applicability of weir-flume combination facility,the influence of outlet width of measuring flume on hydraulic performance and flow measurement of weir-flume combination facility was studied.【Method】Under different flow conditions(5-71 L/s),35 sets of hydraulic performance tests with three measuring flume outlet widths(b=25,35 and 45 cm)were carried.The influence of outlet width on water surface line of middle vertical plane and Froude number(Fr)along the flume was analyzed through the changes of water depth and vertical average velocity of 30 measuring points in the middle vertical plane.Then,the flow thresholds of in-groove flow and weir flow were determined.According to the correlation between inlet-flow(Q)and water depth of measuring point in the flume,the influence of outlet width on the discharge coefficient was analyzed and the flow formula with different outlet widths was established.【Result】Under three different outlet widths,the water depth of the middle vertical plane and Fr showed similar variations along the flume.The water depth of the middle vertical plane was stable in the upstream section and dropped to the thin water layer gradually after entering the measuring flume.Fr was relatively stable in the upstream section(0.1-0.2)and increased to the maximum value(1.2-1.5)gradually after entering the flume,and the increasing rate increased along the flume.The water depths in the upstream section and in the measuring flume decreased with the increase of outlet width.The water depths in the outlet section,thin water layer and backwater area were not greatly affected by outlet width.The Fr from the upstream section to the torsional transition inside the measuring flume increased with the increase of outlet width,but that of the trapezoidal narrow section decreased with the increase of outlet width.Under same outlet widths,the flow coefficient of the in-flume flow increased with the increase of flow rate,while the flow coefficient of the weir flow decreased.Under same relative acting heads,the discharge coefficient of the in-flume flow decreased with the increase of outlet width,while that of the weir flow increased.Based on the established flow formulas under outlet widths of three measuring flumes,relative errors between calculated and measured flow values were all within 2%,expanding the application scope of weir-flume combination facility.【Conclusion】The outlet width of measuring flume had important influence on water depth in upstream and measuring flume.The increase of outlet width increased the flow threshold and overflow capacity of weir-flume combination facility and pushed the critical depth section downstream.