Author(s): M. A. Faheem Sadeque; Hasan Zobeyer
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Keywords: No Keywords
Abstract: Shallow wakes are commonly observed in environmental and geophysical flow systems. Simple fish habitat structure (e.g. fish-rock) is an example that generates 3D turbulent wakes, especially in the near-wake region. Hydraulic modeling tools for fish habitat evaluation is very limited. River2D is a numerical tool with depthaveraged flow approximation that can be used for fish habitat modeling. However, the competency of hydraulic modeling of shallow near-wake flows could not be verified due to unavailability of reliable experimental measurements. A recent experimental study (Sadeque et al. 2009a) of shallow wakes in open channel flows provided detailed velocity measurements in the wake of submerged and surface piercing cylinders. For similar channel properties and approach flow conditions hydraulic model (River2D) generated wake velocities are compared with depthaveraged experimental results of Sadeque et al. (2009a). It was observed that the deviation of wake velocity on the downstream plane of symmetry remains less (～10%) for x≤2D, but increases at x=3D-10D. Transverse profiles of depth-averaged longitudinal mean velocities obtained from River2D were in very good agreement with experimental results for the wakes of surface piercing and slightly submerged cylinders. However, the numerical results were under predicting the velocity profiles in the wakes of deeply submerged and moderately submerged cylinders. Overall the rate of decay of velocity defect was considerably slower in the numerical model than observed in experiments. Therefore, River2D will predict greater region of reduced velocity than in practice. This could be misleading for fish habitat evaluation.
Year: 2009