Experimental and Numerical Study of Three Dimensional Flow Structure at Lateral Intake

Authors
M. A. Omidbeigi
S. A. Ayyoubzadeh
A. Safarzadeh Gendeshmin
A. Safarzadeh Gendeshmin
Abstract
The flow at a channel bifurcation is turbulent, highly three-dimensional (3D) and has many complex
features. There is transverse motion accompanying the main flow and an extensive separation zone
that develops in the branch channel. There are two complex flow regions along the intake channel: one
is the separation zone and the other is the region in which helical motion of water particles forms. This
separation occurs because the flow entering the branch channel has considerable momentum in the
direction of the main channel flow. This zone causes hydraulic and sedimentation problems that must
be known before designing the system. This necessitates a deeper insight into the flow patterns and
shear stress distributions near the solid boundaries. In this research, 3D flow patterns at lateral
diversion were investigated experimentally and numerically. The experimental investigation was
carried out at a T-junction, formed by two channels with rectangular cross-sections. The width of
lateral intake to the main channel was 0.4. 3D velocity measurements were obtained using Acoustic
Doppler Velocimeter at junction region for 11%, 16% and 21% discharge ratios. Fluent mathematical
model was then used to investigate the dividing open-channel flow characteristics. Turbulence was
modeled by Two Equation (k-ε, k-ω) and Reynolds Stress (RSM) turbulence models. The predicted
flow characteristics were validated using experimental data and the proper model was selected for
hydrodynamic and parametric studies. Within the main channel, good agreement was obtained
between all models prediction and the experimental measurements, but within the lateral channel, the
RSM predictions were in better agreement with the measured data, and k-ω predictions was better than
those of k-ε. The comparison of experimental and numerical streamlines at different elevations
showed that the selected model is capable to simulate the most important features of flow at
diversions. The study of the velocity contours at different elevations showed that the velocity
magnitude decreases at main channel, just downstream corner of lateral intake at the near bed levels
and this causes the sedimentation in movable beds. The results showed that the width of separation
zone at lateral intake will decrease and the distance of dividing stream surface from left bank of the
main channel will increase by increasing of the discharge ratio. Investigation of the flow pattern at the
entrance of the lateral intake showed that the secondary flow will form at this section. The dimension
of the secondary flow at near bed elevation will increase by increasing of the discharge ratio and this
causes entering of more bed load into the lateral channel.

Keywords

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Modares Civil Engineering journal
Volume 12, Issue 1
March and April 2012