低柱体雷诺数下柱体上游薄层水流马蹄涡特征研究  

Characteristics of Horseshoe Vortex Upstream of the Cylinder in Shallow Water with Low Cylinder Reynolds Number

作　　者：杨坪坪 张会兰[1,2] 王云琦 王玉杰[1,2] YANG Pingping;ZHANG Huilan;WANG Yunqi;WANG Yujie(Jinyun Forest Ecosystem Research Station,School of Soil and Water Conservation,Beijing Forestry Univ.,Beijing 100083,China;Beijing Eng.Research Center of Soil and Water Conservation,Beijing Forestry Univ.,Beijing 100083,China)

机构地区：[1]北京林业大学水土保持学院重庆缙云山三峡库区森林生态系统国家定位观测研究站,北京100083 [2]北京市水土保持工程技术研究中心,北京100083

出　　处：《工程科学与技术》2019年第1期52-59,共8页Advanced Engineering Sciences

基　　金：中央高校基本科研业务费专项资金资助(2016ZCQ06;2015ZCQ-SB-01);国家自然科学基金资助项目(51309006)

摘　　要：马蹄涡是水下柱体基部产生局部侵蚀的主要动力,目前对大雷诺数深水条件的马蹄涡特征研究广泛,而在低柱体雷诺数浅薄层水流条件下因技术条件限制,试验手段难以准确捕获马蹄涡。为准确掌握在该水流条件下马蹄涡的特征,本研究构建了高分辨率高频的粒子图像测速系统,系统测量了6组浅薄层水流条件下柱体前端的瞬时流场。通过分析平均流场特征提取出流动分离点,采用旋转强度的方法识别马蹄涡进而提取马蹄涡位置及强度,使用Oseen涡和纯剪切的控制方程叠加模拟马蹄涡进而计算出马蹄涡的半径。结果表明:在低柱体雷诺数水流条件下(Re D<5 000),随着柱体雷诺数的增加流动分离点急剧向下游移动,同时马蹄涡急剧向柱体端和床面靠近,其半径减小而旋转强度增加。在浅薄层水流条件下,当柱体直径一定时,随着水深的增加,流动分离点向上游运动,同时马蹄涡向远离柱体端和朝水面运动,马蹄涡的半径增加,且其各项参数显著大于明渠水流条件下的参数。随后,结合已有工作,归纳出分离点、马蹄涡特征随柱体雷诺数增加而经历的不同阶段:当5 000<Re D<8 000流动分离点仍向下游急剧移动,马蹄涡的各项特征保持稳定;当Re D>8 000,流动分离点向下游缓慢移动,马蹄涡的各项参数仍维持稳定。研究结果可为柱体基部科学布设防冲设施提供依据和参考。The horseshoe vortex(HV)is formed at the upstream of a vertical cylinder when flow passes the cylinder and it is responsible for the local scouring at the base of the cylinder.Extensive works had been carried out to investigate the characteristics of HV in open channel flow with high Reynold number and large flow depth.However,it was difficult to measure HV experimentally in low Reynold number and shallow flow depth,in view of limitation of experimental technology.To capture HV accurately in shallow water flow,a high resolution and high frequency particle image velocimetry(HR-PIV)was employed in present study.Subsequently,the flow fields upstream of the cylinder were captured by HR-PIV in 6 experimental groups with shallow flow depth.The separation points of each groups were obtained by analyzing the characteristics of time-averaged flow fields.The HV was calculated byλci criterion whereλci represented the swirling strength of vortex.Then the locations of HV were obtained in accordance with the maximal swirling strength point.In addition,the radius of HV was calculated by superposition of Oseen vortex and pure shear model.The results showed that within a low cylinder Reynolds number(ReD)where ReD<5 000,as the increase of ReD,the location of separation point and HV were rapidly approaching the cylinder simultaneously,whereas the HV moved rapidly towards the flume bed,while the radius of HV decreased and the swirling strength increased.Under shallow water flow conditions and the cylinder diameter keeping constant,as the increase of flow depth,the locations of separation point moved towards upstream;HV moved towards upstream and free surface,simultaneously,while the radius of HV increased.Theses HV parameters in the present flow conditions were larger than those in open channel flows.Derived from previous works,it was found that the separation point and HV would display a different manner as ReD became lager.When 5 000<ReD<8 000,the separation point was still rapidly moving downstream while HV remained stable as i

关 键 词：柱体绕流 马蹄涡 粒子图像测速 薄层水流 低雷诺数 

分 类 号：TV131.2[水利工程—水力学及河流动力学]