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(Islam et al.
2006
). A good knowledge of nodal-point relations is a basic condition
for any kind of morphological study in which bifurcations are involved. Therefore,
this study makes an attempt to find nodal-point relations by 3D flow modeling for
some basic geometries. The relations will be formulated in terms of (
2
) and (
3
), in
which
and
m, n
are analyzed as functions of the previously mentioned factors.
This study is limited to a few cases of the main channel with a diverting branch.
The influence of the discharge distribution, the diverting angle on the distribution of
the sediment is investigated (Meijer and Ksiazek
1994
).
a
,
b
2 Material and Methods
2.1 Mathematical Model
FLUENT is a general-purpose package for 2D or 3D modeling of fluid flow. The
model consists of two parts: preprocessor that allows grid generation and a main
module for defining the physical models and fluid and material properties, and the
boundary conditions (Fluent
1993
).
The model simulates a range of physical phenomena by solving conservation
equations for mass, momentum, and energy using a control volume-based finite
volume method. It solves the Navier-Stokes equations as momentum conservations
and describes turbulence using several turbulence models. The governing equations
are discretized on a curvilinear grid to enable computations in complex geometries.
A non-staggered system is used for storage of discrete velocities and pressures. The
equations are solved using an algorithm with an iterative line-by-line matrix solver
and multigrid acceleration or with the full-field iterative solver.
The model computes trajectories of particles in the flow. The trajectory of a
particle is determined by its diameter, its Reynolds-dependent drag coefficient C
D
,
and the external forces caused by the flow and gravity. The fluctuating component
of this force is related to the turbulence intensity. In this way, several identical
particle releases can yield different trajectories.
2.2 Channel Geometries
Three bifurcation geometries are distinguished, in which the angle of diversion is
varied. In addition, a basic geometry without a diverting channel is added for
preliminary computations in order to judge the computational behavior of the grid,
the numerical convergence, and the adaptation lengths of the inlet conditions. This
results in the following geometries: channel 1 - without bifurcation, and channels 2,
3, and 4 - with bifurcation of 90
, 45,
and 135
, respectively (Fig.
1
). The
