FLOW AROUND A CYLINDER - istiarto

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than the measured one. The strong vorticity peaks (positive and negative ones) in the
bottom corner of the cylinder are missed by the simulation. This is due, as has been
mentioned in the preceding section, to the inability of the simulation to reproduce the
strong reversed flow at this location, which is caused by the limited spatial resolution
of the grid.
� In the plane � = 90° (Fig. 5.19c,d), the vorticity fields show small activity since the
velocity components on this plane are very small as shown in the preceding section.
Nevertheless, the contour plot near the bed indicates a reasonable agreement between
the simulation and the measurement.
� In the plane � = 180° (Fig. 5.19e,f), the simulation and the measurement exhibit
surprisingly a good agreement. The vorticity, being rather small, is distributed more
or less evenly over the plane and there is no region of concentrated vorticity.
Turbulent kinetic energy around the cylinder
Discussed in this section is the turbulent kinetic energy computed by the model. The
computed turbulent kinetic energy is presented as an equivalent height (energy per unit
weight), k g [mm], as shown in Fig. 5.20. For the sake of comparison, plotted also in the
same figure are the values obtained from the experimental data; here the turbulent kinetic
energy is obtained by k � 1 2 u �� u ���
v �� v ���
w ��w
��
following remarks:
� � (see Chapter 3). The figures allow the
� The plots show that the comparison of the computed and measured turbulent kinetic
energy can be considered good. The simulation results in a lower energy than the
measurement, but the tendency of the overall distributions is rather well predicted.
� In the plane � = 0° (Fig. 5.20a,b), both simulation and measurement show high
energy concentrations in the bottom corner of the cylinder. The computed maximum
value shown at the corner vicinity of the cylinder, however, is considerably lower
than the measured one. This is consistent with the difference observed between the
computed and the measured velocities (and vorticities) at this particular location as
discussed in the preceding sections. From the simulation, the high energy is also
observed almost along the entire depth at close vicinity of the cylinder. Unfortunately,
measurements in this region are not available along the entire depth.
� In the plane � = 90° (Fig. 5.20c,d) similar observations as in the plane � = 0° can be
made, but the simulation at the bottom corner of the cylinder is better, showing a
close comparison to the measured data.
� In the plane � = 180° (Fig. 5.20e,f) the simulation and the measurement show a
similar pattern, but the under-estimation of the kinetic energy is also considerable as
in the plane � = 0°.