Time-averaged sub-layer concentration profiles in oscillatory sheet flows  

作　　者：Yuhai Wang Wenhong Cao Wen Lu Huifeng Liu Gauhu Sun Chonghao Wang Fei Liu 

机构地区：[1]State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research

出　　处：《International Journal of Sediment Research》2018年第4期433-440,共8页国际泥沙研究（英文版）

基　　金：supported by grants from the National Key Research and Development Program of China (2017YFC0405504);the National Natural Science Foundation of China (51179211);the Basic Research Special Fund of IWHR (SE0145B142017)

摘　　要：Although thin on the order of several to tens of millimeters, sheet flows normally comprise a lower pick- up sub-layer and an upper contact-load sub-layer, separated at the bed level （z = 0）. The time-averaged concentration profile in the pick-up sub-layer shows a ＇convex upward＇ curvature, but ＇concave upward＇ shape characterizes the time-averaged concentration profile in the contact-load sub-layer. The time- dependent concentration in the contact-load sub-layer is approximately in-phase with the free stream flow velocity, whereas it is nearly in anti-phase with the free stream flow velocity in the pick-up sub- layer. Two distinct analytical expressions of the time-averaged concentration profiles for the respective sub-layers are proposed. The expressions are validated with detailed observation datasets collected in the Groβer Wellenkanal （GWK） prototype wave flume in Hannover, Germany. The agreement between the predicted and the measured values is excellent. Interparticle collisions in the pick-up sub-layer and convective lifting processes associated with vortex shedding in the contact-load sub-layer are considered responsible for the opposite curvatures and in-phase/anti-phase concentration variations. Both transi- tional boundary and reference concentration are also elaborated.Although thin on the order of several to tens of millimeters, sheet flows normally comprise a lower pick- up sub-layer and an upper contact-load sub-layer, separated at the bed level （z = 0）. The time-averaged concentration profile in the pick-up sub-layer shows a ＇convex upward＇ curvature, but ＇concave upward＇ shape characterizes the time-averaged concentration profile in the contact-load sub-layer. The time- dependent concentration in the contact-load sub-layer is approximately in-phase with the free stream flow velocity, whereas it is nearly in anti-phase with the free stream flow velocity in the pick-up sub- layer. Two distinct analytical expressions of the time-averaged concentration profiles for the respective sub-layers are proposed. The expressions are validated with detailed observation datasets collected in the Groβer Wellenkanal （GWK） prototype wave flume in Hannover, Germany. The agreement between the predicted and the measured values is excellent. Interparticle collisions in the pick-up sub-layer and convective lifting processes associated with vortex shedding in the contact-load sub-layer are considered responsible for the opposite curvatures and in-phase/anti-phase concentration variations. Both transi- tional boundary and reference concentration are also elaborated.

关 键 词：Sheet flow SUB-LAYER Time-averaged concentration profile Suspension mechanism 

分 类 号：TV139.25[水利工程—水力学及河流动力学]