HR: 1330h
AN: H12B-1005    [PDF]
TI: Computational Modeling of Self-Preserving Turbulent Wall Jets and Associated Scour
AU: * Anderson, E K
EM: ekanderson@ucdavis.edu
AF: University of California, Davis Civil and Environmental Engineering Department, One Shields Avenue, Davis, CA 95616 United States
AB: Turbulent wall jets frequently occur in the natural environment (e.g. avalanches, turbidity currents) and have therefore been the focus of many theoretical and experimental studies aimed at understanding their behavior and impact on bed scour. From a computational perspective, wall jets are relatively straightforward to compute, but difficult to predict accurately using eddy-viscosity turbulence models. Essentially, the wall jet can be viewed as a combination of two separate layers: a wall boundary layer and a free mixing layer; the interactions between the two being responsible for many of this flows interesting features. Simulations of turbulent wall jets presented here involve solving the Reynolds-averaged Navier-Stokes equations and providing an appropriate model for the Reynolds stresses, the terms which contain the shear stresses associated with turbulence problems. We report on the use of two distinct classes of turbulence models: (1) a second-order closure model of turbulence based on the solution of modeled transport equations for all non-zero components of the Reynolds-stress tensor and, (2) a two-equation, eddy-viscosity model of the type frequently used in environmental applications. The models are tested for their ability to predict the hydrodynamic behavior of turbulent jets developing over plane smooth surfaces with emphasis on the behavior of the wall shear stress. The predicted wall shear stress can later be used to assess scour. Emphasis is placed on the special class of self-similar flows which, for wall jets, requires the ratio of the maximum-to-free stream velocities to be constant with streamwise distance. In this study, we consider values of this ratio from 0 to 0.8: the zero case corresponding to the challenging case of a wall jet developing in stagnant surroundings, a common occurrence in natural systems. The primary interest is the accurate prediction of the rate at which the jet expands into the surrounding environment, and the wall shear stresses that are the cause of severe scour associated with turbulent wall jets. We present comparisons with experimental data and with empirical correlations. These show that the second-order closure model succeeds in capturing many of the important features of this complex flow, including the separation of the points where the turbulent shear stress and the mean velocity gradients are zero. The wall shear stresses are also well predicted with this model but less so with the two-equation model. The implications of these results on the prediction of bed-load sediment transport will be discussed.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2003 Fall Meeting