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

• Published in: International journal of sediment research 2015-12, Vol.30 (4), p.297-305
• Main Authors: Spiller, Stephan M., Rüther, Nils, Baumann, Benjamin
• Format: Article
• Language: English
• Subjects: 下线; 服务; 迁移
• ISSN: 1001-6279
• DOI: 10.1016/j.ijsrc.2014.10.002

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.