Form-induced stress in non-uniform steady and unsteady open channel flow over a static rough bed  

作　　者：Stephan M. Spiller Nils Ruther Benjamin Baumann 

机构地区：[1]Hydraulic Engineering, Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens veg 5,7491 Trondheim, Norway

出　　处：《International Journal of Sediment Research》2015年第4期297-305,共9页国际泥沙研究（英文版）

摘　　要：This paper presents a series of 18 steady and 45 unsteady flow experiments over an artificial, rough surface, obtained by a novel molding technique for gravel beds. Velocity data are obtained by a Particle Image Velocimetry （PIV） system. The vertical distributions of the form-induced stresses （u） and -（uw） are compared for all experiments, Furthermore, quadrant maps are drawn to analyze the near bed spatial velocity fluctuations u and w in a vertical plane parallel to the flow direction. All experiments were done under non-uniform flow. It is shown that （1） the qualitative shape of the vertical form-induced stress distributions （u2） and -（uw） is independent from the discharge, as stated in the literature, as well as from the unsteadiness of the flow. （2） The magnitude of the form-induced stress （u2） and -（uw） in the roughness layer increases with increasing discharge for non-uniform flow, while uniform flow experiments in the lit- erature report the form-induced stresses to be independent from the discharge. A hypothesis is, therefore, proposed, that the independence of the form-induced stress magnitude from the discharge is only valid for uniform flow. （3） Quadrant maps, describing the distribution of the spatial fluctuations u and w in a twodimensional plane are independent from discharge and unsteadiness of the flow.This paper presents a series of 18 steady and 45 unsteady flow experiments over an artificial, rough surface, obtained by a novel molding technique for gravel beds. Velocity data are obtained by a Particle Image Velocimetry （PIV） system. The vertical distributions of the form-induced stresses （u） and -（uw） are compared for all experiments, Furthermore, quadrant maps are drawn to analyze the near bed spatial velocity fluctuations u and w in a vertical plane parallel to the flow direction. All experiments were done under non-uniform flow. It is shown that （1） the qualitative shape of the vertical form-induced stress distributions （u2） and -（uw） is independent from the discharge, as stated in the literature, as well as from the unsteadiness of the flow. （2） The magnitude of the form-induced stress （u2） and -（uw） in the roughness layer increases with increasing discharge for non-uniform flow, while uniform flow experiments in the lit- erature report the form-induced stresses to be independent from the discharge. A hypothesis is, therefore, proposed, that the independence of the form-induced stress magnitude from the discharge is only valid for uniform flow. （3） Quadrant maps, describing the distribution of the spatial fluctuations u and w in a twodimensional plane are independent from discharge and unsteadiness of the flow.

分 类 号：U469.11[机械工程—车辆工程] X53[交通运输工程—载运工具运用工程]