FLOW AROUND A CYLINDER - istiarto

The following is to be observed:
– 3.25 –
� In the plane � = 0° and approaching the cylinder, there is an increase in the turbulent
kinetic energy over the entire scour hole. A distinguishable feature is the pronounced
bulges immediately below the original bed level whose intensity and form enlarge
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approaching the cylinder (see Fig. 3.10a). The bulges, ranging between k u�,� ≈ 7
to 45, correspond to the isoline of 0.1(K+k) turbulent kinetic energy (see Fig. 3.11a),
which delimitates the region of high turbulent energy inside the scour hole (as high as
90% of the total kinetic energy) from the one of low level turbulent outside the scour
hole. The maximum value of the turbulent kinetic energy is found at the bottom
corner of the cylinder where the strong reversed flow (see Fig. 3.2) and the vorticity
peak (see Fig. 3.8) are observed.
� In the plane � = 45°, the same as in the plane � = 0° is observed, but a slightly lower
turbulent energy peak at the bottom corner of the cylinder.
� In the plane � = 90°, the high turbulent kinetic energy is almost in the entire scour
hole; the bulges seen in the preceding planes are here nearly extended (see Fig. 3.10c)
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with a maximum value of k u�,� ≈ 40. The kinetic energy inside the scour hole, as
in the planes � = 0° and 45°, is largely due to the turbulence; it peaks at 90% of the
total kinetic energy in the lower part of the scour hole at r ≤ 20 [cm] (see Fig. 3.11c).
� In the plane � = 135°, the trend seen in the plane � = 90° continues; moving away
from the cylinder, the bulges in the kinetic energy profiles diminish.
� In the plane � = 180°, there is a significant increase in the turbulent kinetic energy;
this is observed in the entire flow depth. At the vicinity of the cylinder, a peak value
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of k u�,� ≈ 45 is measured until r = 20 [cm]. Leaving the cylinder and the scour
hole, the turbulent kinetic energy gradually reduces (see Fig. 3.10e) and at
r = 100 [cm] is becomes less than 10% of the total kinetic energy (see Fig. 3.11e).
Again, it should be noted that the measured data must be interpreted with caution. In
this wake region, the flow is chaotic, with a vortex shedding taking place; it is
possible that the measurements do not have a sufficiently time resolution to resolve
this shedding movement.