Abstract: The turbulent structures in the wake (x/d =10 to 60) of a screen cylinder have been educed to understand the roles of the various structures as evolving downstream by comparing with those obtained in a solid circular cylinder wake at Reynolds number, Re of 7000. Using a wavelet multiresolution technique, the flow structures are decomposed into a number of wavelet components based on their central frequencies. It is observed that in the solid cylinder wake, large-scale structures (of frequencyf0 and 1.2 f0) make the largest contribution to the Reynolds stresses although they start to lose their roles significantly at x/d> 20. In the screen cylinder wake, the intermediate-scale structures (2f0 and 4f0) contribute the most to the Reynolds stresses atx/d =10 before being taken over by the large-scale structures (f0) further downstream.
Abstract: Thewake flow behind two yawed side-by-sidecircular
cylinders is investigated using athree-dimensional vorticity probe.
Four yaw angles (α), namely, 0°, 15°, 30° and 45° and twocylinder
spacing ratios T*
of 1.7 and 3.0 were tested. For T*
= 3.0, there exist
two vortex streets and the cylinders behave as independent and
isolated ones. The maximum contour value of the coherent streamwise
vorticity ~* ωx
is only about 10% of that of the spanwise vorticity ~* ωz
.
With the increase of α,
~* ωx
increases whereas ~* ωz
decreases. At α =
45°, ~* ωx
is about 67% of ~* ωz
.For T* = 1.7, only a single peak is
detected in the energy spectrum. The spanwise vorticity contours have
an organized pattern only at α = 0°. The maximum coherent vorticity
contours of ~* ω x
and ~* ωz
for T*
= 1.7 are about 30% and 7% of those
for T*
= 3.0.The independence principle (IP)in terms of Strouhal
numbers is applicable in both wakes when α< 40°.