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Effects of bed roughness on flow around bed-mounted cylinders in open channels / M. A. F. Sadeque in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 100-110 Titre : Effects of bed roughness on flow around bed-mounted cylinders in open channels Type de document : texte imprimé Auteurs : M. A. F. Sadeque, Auteur ; N. Rajaratnam, Auteur ; M. R. Loewen, Auteur Article en page(s) : pp. 100-110 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Open  channel  flow  Boundary  layers  Flow  visualization  Shear  stress  Bed  roughness  Fish  management. Résumé : This paper presents the results of an experimental study of flow around cylindrical objects on a rough bed in an open channel. This is an extension of a previous study of flow around cylinders on a smooth bed. The purpose of this study is to explore the effects of bed roughness on the characteristics of the deflected flow around cylindrical objects and the resulting bed-shear stress distributions. Similar to the previous study cylindrical objects of equal diameter and four heights were tested under similar flow conditions producing four different levels of submergence. Bed shear stress and deflected flow velocities were measured by a thin yaw-type Preston probe after a set of flow visualization tests. Flow visualization tests showed that the horse-shoe vortex systems on the rough bed occupy a relatively greater width compared to the smooth bed. Unlike smooth bed observations, the flow separation point upstream of the cylinder was not dependent on the level of submergence as the separation points were found to appear within a short range of x=−1D to −1.2D. Bed shear stress has been found to increase significantly near the shoulder of the cylinders, and its ratio with respect to the approach bed-shear stress was twice as large compared to the smooth bed case. Mean velocity profiles were analyzed in terms of three-dimensional turbulent boundary layer theories. Bed roughness was found to oppose the effect of the lateral pressure gradient that causes skewing in the boundary layer. Perry and Joubert's model has been found to be equally accurate on smooth and rough beds for predicting the deflected velocity magnitudes around cylinders. The present study will enhance the knowledge of hydraulics of flow around bed-mounted objects (e.g. fish-rocks) in natural streams. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Effects of bed roughness on flow around bed-mounted cylinders in open channels [texte imprimé] / M. A. F. Sadeque, Auteur ; N. Rajaratnam, Auteur ; M. R. Loewen, Auteur . - pp. 100-110. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 100-110 Mots-clés : Open  channel  flow  Boundary  layers  Flow  visualization  Shear  stress  Bed  roughness  Fish  management. Résumé : This paper presents the results of an experimental study of flow around cylindrical objects on a rough bed in an open channel. This is an extension of a previous study of flow around cylinders on a smooth bed. The purpose of this study is to explore the effects of bed roughness on the characteristics of the deflected flow around cylindrical objects and the resulting bed-shear stress distributions. Similar to the previous study cylindrical objects of equal diameter and four heights were tested under similar flow conditions producing four different levels of submergence. Bed shear stress and deflected flow velocities were measured by a thin yaw-type Preston probe after a set of flow visualization tests. Flow visualization tests showed that the horse-shoe vortex systems on the rough bed occupy a relatively greater width compared to the smooth bed. Unlike smooth bed observations, the flow separation point upstream of the cylinder was not dependent on the level of submergence as the separation points were found to appear within a short range of x=−1D to −1.2D. Bed shear stress has been found to increase significantly near the shoulder of the cylinders, and its ratio with respect to the approach bed-shear stress was twice as large compared to the smooth bed case. Mean velocity profiles were analyzed in terms of three-dimensional turbulent boundary layer theories. Bed roughness was found to oppose the effect of the lateral pressure gradient that causes skewing in the boundary layer. Perry and Joubert's model has been found to be equally accurate on smooth and rough beds for predicting the deflected velocity magnitudes around cylinders. The present study will enhance the knowledge of hydraulics of flow around bed-mounted objects (e.g. fish-rocks) in natural streams. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]