| | | Document Type | : | Latin Dissertation | | Language of Document | : | English | | Record Number | : | 54289 | | Doc. No | : | TL24243 | | Call number | : | NR45590 | | Main Entry | : | Muhammad Abdul Faheem Sadeque | | Title & Author | : | Structure of turbulent flows around bed-mounted cylinders in open channelsMuhammad Abdul Faheem Sadeque | | College | : | University of Alberta (Canada) | | Date | : | 2008 | | Degree | : | Ph.D. | | student score | : | 2008 | | Page No | : | 400 | | Abstract | : | An experimental investigation of the characteristics of shallow turbulent wakes behind bed-mounted cylinders in an open channel was carried out. Cylindrical objects of equal diameter and four heights were tested under similar flow conditions on smooth and rough beds producing four different levels of submergence. As a part of the systematic approach followed in this study, properties of the undisturbed approach flow have been studied first. The altered flow patterns in the upstream region surrounding the cylinders are studied along with a study of the skewed turbulent boundary layer. In addition, flow visualization and detailed measurements of the bed shear stress around the cylinders are presented. The principal motivation for this study is to improve our understanding of the flows around simple fish habitat structures. Analysis of the flow field around the cylinders in terms of the theories of three-dimensional turbulent boundary layers revealed that Perry and Joubert's model is sufficiently accurate to predict the deflected velocity magnitudes around the submerged and non-submerged cylinders. The general flow patterns in the shallow near-wake region were explained using reliable velocity measurements. The mean velocity defect and wake turbulence were found to increase in the near-wake before decaying in the downstream direction. The rates of decay of the velocity defect and wake turbulence were related to the level of submergence of the cylinders and bed roughness. Wall wake analyses demonstrated that the flows in the region away from the bed are quite similar and can be described with the well-known plane wake equation. Wall wake similarity was also observed for the turbulence properties, such as the turbulent kinetic energy and primary Reynolds stress for moderate to deeply submerged cylinders. Wake analyses on the horizontal plane showed that the mean velocity profiles were similar across the flow in the near-wake region at all elevations for slightly submerged and surface piercing cylinders; and at all elevations below the object height very close to the moderate to deeply submerged cylinders. Normalized mean velocity profiles across the wake in the horizontal plane for slightly submerged and surface piercing cylinders were in fair agreement with the well-known plane wake equation. However, the normalized mean velocity profiles were found to exhibit considerable similarity in all flow regimes when a slightly modified transverse length scale (i.e. half-width) was used. | | Subject | : | Applied sciences; Turbulent flows; Bed-mounted cylinders; Open channels; Civil engineering; 0543:Civil engineering | | Added Entry | : | University of Alberta (Canada) |
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