Geoscience Reference
In-Depth Information
Fig. 30 Scheme of horseshoe
vortex upstream the cylinder
in the scour hole (Adapted
from Muzzammil and
Gangadhariah
2003
)
HORSESHOE
VORTEX
h
h
s
b
1
POSITION
OF EDGE
(RIM)
a
1
PIER LEADING
EDGE
Fig. 31 Schematic flow
pattern inside the scour hole
in front of the pier (Adapted
from Unger and Hager
2007
)
Unger and Hager (
2007
) investigated the characteristics of the internal flow
upstream a half-cylinder placed on the side wall of a channel. They performed a
detailed temporal description of the horseshoe vortex with PIV. The placement of
the cylinder at the lateral wall of the channel allows better visualization of the flow
phenomena and a better quality of the data obtained. However, the turbulent
boundary layer existent along the wall influences the flow behavior, so the results
cannot be directly compared with those obtained in the plane of symmetry of the
channel. These authors suggest that the equivalent vortex is located at the point of
intersection of the two slopes in the scour hole, over the cusp (Fig.
31
), rather than
located in the greater slope, as defendend by Muzzammil and Gangadhariah (
2003
).
They concluded that both the horseshoe vortex inside the continuously increas-
ing scour hole and the downflow in front of the pier are the governing scour agents.
