Abstract:
The aim of this research work was to investigate and increase the understanding of
three dimensional flow behavior under changing conditions of flow and sediments.
The goal was achieved by using a 3D Computational Fluid Dynamics model
FLUENT.
The geometry selected for this study is that of a meandering compound channel. The
parameters which were changed in this research work include the width of floodplain
along with main channel width, overbank flow depth, incoming discharge, bed slope
of the main channel and floodplains and roughness of the channel and floodplains.
The research work was conducted by using different turbulence models. Among them
are standard k , Re-normalization Group (RNG) theory based k and k
turbulence models. These three models were applied for one case. Once the capability
of k model was established after comparison with results of other models, then
only k was used in the remaining part of the work. The data obtained from a
physical model study in the laboratory was used for the validation of simulated
results. The validation was done through a comparison of observed and calculated
values of depth averaged velocities, total discharge at a section & point velocities.
After validation, the CFD model was used to predict and investigate those aspects of
flow which were difficult to get through experiments and for which experimentation
was not conducted in the laboratory. These aspects include turbulence intensity,
turbulent kinetic energy, pressure distribution on different cross sections of the
channel and surface velocity magnitudes. As far as the sediments study is concerned,
the Lagrangian particle tracking technique was used to predict the changes in bed
levels at apex of the meander wavelength. Sediment particles with different diameters
were used for this purpose.
A total of eight flow cases were considered for the study of flow field. Each case
varies from the other on the basis of (i) geometry or (ii) bed slope or (iii) depth of
overbank flow or a combination of these. This work also proved the capability of
standard k turbulence closure models in prediction of 3D overbank flows.
Keywords: Sediment transport, CFD modeling, Flood flows, Numerical techniques,
Turbulent kinetic energy.
