FLOW AROUND A CYLINDER - istiarto

– 2.47 –
Turbulence intensities in the plane 90°. In the far region, the turbulence intensity
distributions resemble the one in the uniform approach flow. In the scour-hole region and
approaching the cylinder, the distributions keep constant within the upper layer and
increase within the lower layer. At the upper layer, the u �� u �� is always dominant,
followed by, successively, the v �� v �� and w ��w
��.
At the lower layer, however, the
v �� v �� eventually exceeds the u �� u �� and becomes the most prominent; at r = 10 [cm], the
values are v �� v �� ≈ 0.15 [m/s] and u �� u �� ≈ 0.09 [m/s]. Compared to the planes � = 0°
and 45°, the u �� u �� component shows similar tendency, except at r = 10 [cm] where it
exhibits a decrease. For the other two components, there is a modest increase.�
Reynolds stresses in the plane � = 90°. The Reynolds stress in the far region, as in the
case of the velocity, does not show any noticeable change due to the cylinder. In the
scour-hole region and approaching the cylinder, the �u �� w ��stays
more or less constant at
the upper layer and increases at the lower layer, while the �v �� w �� becomes more
pronounced. The �u �� w �� at the lower layer shows a sharp turn towards a peak underneath
z = 0, as also in the case of the planes � = 0 and 45° but with considerably higher values.
Approaching the cylinder from r = 44 to 22 [cm], this peak increases from �u �� w �� ≈ 0.001
to 0.004 [m2 /s2 ], but further approaching the cylinder, this peak decreases to
�u �� w �� ≈ 0.0015 [m2 /s2 ] at r = 10 [cm]. There is a negative �u �� w ��-value
at
15 ≤ r [cm] ≤ 26 and close to the bed; this corresponds with the negative u-component
and the upward w-component previously presented. The �v �� w �� has a distribution in
alternating negative-positive-negative values with the depth. Closer to the cylinder, the
negative value becomes dominant and at r = 10 [cm], the �v �� w �� all takes the negative
value. Compared to the planes � = 0° and 45°, the �v �� w �� is generally higher.�
2.5.6 Measurements in the plane � = 135°
The scour hole in the plane � = 135° extends up to r = 90 [cm] (6D p) with the maximum
scour depth of ds = 21.3 [cm] (1.4h∞) at the leading edge of the cylinder. Unlike the
previous planes, there is no single, but a double inclination of the scour hole. The
measurements at this plane were performed at 10 ≤ r [cm] ≤ 80, from which 16 vertical
distributions of the velocities, the turbulence intensities, and Reynolds stresses were
obtained. The data are available in the entire depth (zones A and B) for r ≥ 22 [cm] but
are only available at z ≤ 5 [cm] (zone B) for r ≤ 18 [cm]. Shown in Fig. 2.15 are the
measured distributions for 10 ≤ r [cm] ≤ 70; the data at r = 80 [cm] are not shown.
Velocities in the plane � = 135°. The u-component is always dominant among the other
components, v and w. Approaching the cylinder, the u-component gradually increases
and is always positive. At the same time, the v- and w-components get more important
but remain smaller than the u-component. The v-component is vertically distributed in an
alternating negative-positive value, but close to the cylinder, it shifts towards the positive
side. At r = 10 [cm], it is positive along the entire depth of measurement with the
maximum value of v ≈ 0.15 [m/s] (0.33U∞). The w-component manifests itself as a
downward velocity, except close to the bed where there is an upward component. The