TY - JOUR
T1 - Form-induced stress in non-uniform steady and unsteady open channel flow over a static rough bed
AU - Spiller, Stephan M.
AU - Rüther, Nils
AU - Baumann, Benjamin
N1 - Publisher Copyright:
© 2015 International Research and Training Centre on Erosion and Sedimentation / the World Association for Sedimentation and Erosion Research.
PY - 2015/12/1
Y1 - 2015/12/1
N2 - 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~2〉 and -〈u~w~〉 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 〈u~2〉 and -〈u~w~〉 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 〈u~2〉 and -〈u~w~〉 in the roughness layer increases with increasing discharge for non-uniform flow, while uniform flow experiments in the literature 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 two-dimensional plane are independent from discharge and unsteadiness of the flow.
AB - 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~2〉 and -〈u~w~〉 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 〈u~2〉 and -〈u~w~〉 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 〈u~2〉 and -〈u~w~〉 in the roughness layer increases with increasing discharge for non-uniform flow, while uniform flow experiments in the literature 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 two-dimensional plane are independent from discharge and unsteadiness of the flow.
UR - http://www.scopus.com/inward/record.url?scp=84949228387&partnerID=8YFLogxK
U2 - 10.1016/j.ijsrc.2014.10.002
DO - 10.1016/j.ijsrc.2014.10.002
M3 - Article
AN - SCOPUS:84949228387
SN - 1001-6279
VL - 30
SP - 297
EP - 305
JO - International Journal of Sediment Research
JF - International Journal of Sediment Research
IS - 4
ER -