14 research outputs found
Dynamic drag modeling of submerged aquatic vegetation canopy flows
Vegetation has a profound effect on flow and sediment transport
processes in natural rivers, by increasing both skin friction and form
drag. The increase in drag introduces a drag discontinuity between the
in-canopy flow and the flow above, which leads to the development of an
inflection point in the velocity profile, resembling a free shear layer.
Therefore, drag acts as the primary driver for the entire canopy system.
Most current numerical hydraulic models which incorporate vegetation
rely either on simple, static plant forms, or canopy-scaled drag terms.
However, it is suggested that these are insufficient as vegetation
canopies represent complex, dynamic, porous blockages within the flow,
which are subject to spatially and temporally dynamic drag forces. Here
we present a dynamic drag methodology within a CFD framework.
Preliminary results for a benchmark cylinder case highlight the accuracy
of the method, and suggest its applicability to more complex cases
Two-dimensional analytical solution for compound channel flows with vegetated floodplains
Spatial Variability, Mean Drag Forces, and Drag Coefficients in an Array of Rigid Cylinders
Lateral distributions of streamwise velocity in compound channels with partially vegetated floodplains
Flow characteristics and morphological changes in open-channel flows with alternate vegetation zones
Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river
The patterns of depth, velocity, and shear stress that direct a river's morphologic evolution are governed by a balance of forces. Analyzing these forces, associated with pressure gradients, boundary friction, channel curvature, and along- and across-stream changes in fluid momentum driven by bed topography, can yield insight regarding the establishment and maintenance of stable channel forms. This study examined how components of the local force balance changed as a meandering channel evolved from a simple, flat-bedded initial condition to a more complex bar-pool morphology. A numerical flow model, constrained by measurements of velocity and water surface elevation, characterized the flow field for four time periods bracketing two floods. For each time increment, runs were performed for discharges up to bankfull, and individual force balance components were computed from model output. Formation and growth of point bars enhanced topographic steering effects, which were of similar magnitude to the pressure gradient and centrifugal forces. Convective accelerations induced by the bar reduced the cross-stream pressure gradient, intensified flow toward the outer bank, and routed sediment around the upstream end of the bar. Adjustments in the flow field thus served to balance streamwise transport along the inner bank onto the bar and cross-stream transport into the pool. Even in the early stages of bar development, topographically driven spatial gradients in velocity played a significant role in the force balance at flows up to bankfull, altering the orientation of the shear stress and sediment transport to drive bar growth. Copyright 2011 by the American Geophysical Union