FLOW AROUND A CYLINDER - istiarto

– 2.58 –
As the flow advances to the downstream passing the scour hole, the intensity of the
turbulence gets stronger. The increase of the turbulence level is notably noticeable from
the plane � = 90° to � = 135°. This increase continues, but with diminishing rate, in the
plane � = 180°. In this downstream plane, the turbulence demonstrates its peak intensity.
It is interesting to observe that, in this plane, the three components of the intensity,
u �� u ��,
v �� v �� and w ��w
��,
indicate a tendency of being isotropic. Observing the intensity
of the turbulence in each plane, one can notice that, approaching the cylinder, the
turbulence inside the scour hole intensifies. In the upper layer, on the other hand, the
turbulence level remains more or less constant.
Approaching the cylinder, in all planes except in the plane � = 180°, the turbulence
intensifies within the scour hole, z < 0, but remains more or less unchanged outside the
scour hole, z > 0. Downstream of the cylinder, in the plane � = 180°, the turbulence gets
its strongest intensities.�
The Reynolds shear-stresses inside the scour hole gets increasingly stronger as the flow
moves towards downstream from the plane � = 0° to � = 135°. In the plane � = 135°, the
stresses are about 3 times higher than those in the plane � = 0°. In the upper layers, z > 0,
the profiles of the Reynolds stresses exhibit a nearly linear distribution. Underneath,
z ≤ 0, the profiles of the Reynolds stresses turn towards a strong peak. In all planes, the
�u �� w �� is always dominant compared to the �v �� w ��.
Downstream of the cylinder,
� = 180°, the vertical distributions of the Reynolds stresses do not show any conclusive
trend.�
References
Cellino, M. (1998). Experimental study of suspension flow in open channels., Doctoral
Dissertation, No. 1824, EPFL, Lausanne, Switzerland.
Graf, W. H., and Altinakar, M. S. (1996). Hydraulique Fluviale, Tome 2., P.P.U.R.,
Lausanne, Switzerland.
Graf, W. H., and Altinakar, M. S. (1998). Fluvial Hydraulics., John Wiley & Sons, Ltd.,
Chichester, England.
Hurther, D., Lemmin, U., and Arditi, M. (1996). ―Using an annular curved array
transducer for bistatic ADVP application.‖ Rapport Annuel, Laboratoire de
recherches hydrauliques, EPFL, 1996, B.201.1-B.201.19.
Kironoto, B. A., and Graf, W. H. (1994). ―Turbulence characteristics in rough uniform
open-channel flow.‖ Proc. Instn. Civ. Engrs. Wat., Marit. & Energy, 106, 333-344.
Lhermitte, R., and Lemmin, U. (1994). ―Open-channel flow and turbulence measurement
by high-resolution Doppler sonar.‖ J. Atm. Ocean. Tech., 11, 1295-1308.
Nezu, I., and Nakagawa, H. (1993). Turbulence in open-channel flows., A.A. Balkema,
Rotterdam, NL.