poster - International Conference of Agricultural Engineering

the experimental results and close to the Eq. 6 with an increase in fetch except the upstream
part of tank. This indicates that the prediction model well reproduced the development of
wind-wave obtained by the hydraulic experiment.
20cm
8cm
Flow
17.6cm
Air phase
160cm
Water phase
(a) The shape of interface
(b) The power spectrum
FIGURE 4: The interface shape and the the power spectrum of wind wave
Since this numerical model deals with air and water phases, the characteristics of vertical
transport of vortex through the water surface can be considered. Fig. 5 shows the isosurface
of the second invariant of velocity gradient tensor Q in the air and liquid phases at the 10
seconds. Q represents the local balance between the shear strain rate and vorticity
magnitude. The region of positive implies the the rotation tensor dominates over the rate of
strain tensor. In addition, the color distributuion at the water surface represents the turbulent
intensity of the velocity in the flow direction. This figure illustrates that two-dimensional vortex
structure is formed along the lines with the wind wave which develops in parallel to the span
direction at the air and liquid phases, respectively. This indicates the wind induced flow has a
vortex structure with a strong three-dimensional feature.
z
y
x
(a) Air phase
(b) Water phase
FIGURE 5: The isosurface of the second invariant of velocity gradient tensor
Finally, we discuss the effect of the coverage on the development of wind wave and the
characteristics of circulation flow. Fig. 6 shows the shape of water surface and the velocity
distribution near the coverage in case of Type A. The shape of water surface indicates that
the development of water surface wave is inhibited by the existence of the coverage. Then,
the wave height decrease significantly behind the coverage. Moreover, the velocity is large in
the vicinity of the water surface in front of the coverage, and it seems to be transported
downstream under the board. The velocity around the back edge of coverage is very small,
but in the vicinity of the water surface it starts to grow again. In this way, two wind-induced
circulations are formed.
y
z
x