Measurement configurations. (a) Side-view configuration and (b) upstream-view configuration.
Instantaneous spanwise vorticity contours after merging, [Re = 180]. Two different frames are labeled as frame 1 and frame 2 and indicated with arrows. To assess the averaging methods which are given on the right hand side velocity and vorticity data are extracted along the indicated line.
Extracted spanwise vorticity, horizontal and vertical velocity profiles after weighted averaging in the overlapping region. Each symbol in the figures corresponds to a PIV grid point.
u rms /U ∞ profiles in the near-wake at two different Reynolds numbers (Re = 185, 230) and three downstream positions (x/D = 1.5, 4.5, 12). (a) Wire: Re = 180, no wire: Re = 185; (b) wire: Re = 225, no wire: Re = 230.
Instantaneous pattern of non-dimensional spanwise ω z D/U ∞ (left figure) and streamwise ω x D/U ∞ (right figure) vorticity. Streamwise vorticity is measured at cross-stream plane x/D = 4.5 at the corresponding von Kármán vortex shedding phase in the left figure. Contour levels are |ω z |D/U ∞ = 0.4, 0.8, …, 4 and |ω x |D/U ∞ = 0.2, 0.4, …, 2. Solid line (blue online) and dashed line (red online) contours indicate positive and negative vorticity, respectively, at Re = 180.
Downstream variation of maximum levels of u rms | max /U ∞ in the upper half of the wake. (a) No wire; (b) wire.
Example of an energy spectrum and corresponding discrete energy intensities. Energy spectrum is obtained from side-view PIV experiment for Re = 180 at data point (x/D, y/D) = (4.5, 1.0).
Comparison of wake energy intensity and integrated energy obtained from rms and spectrum calculation of side-view PIV experiments. The energy intensity plots show cross-stream data profiles at x/D = 4.5. (a) Energy intensity, e; (b) integrated energy, E.
(a) and (b) Discrete energy components in Mode-C wake which are calculated at specific frequencies of the energy spectrum on the cross-stream line at x/D = 4.5.
Downstream variation of total wake energy E for wired and non-wired cylinders.
Downstream variation of total (E 0 + E 1)/E and discrete energy ratios E 0/E and E 1/E in the wake of a wired cylinder at Re = 180 and Re = 225.
Instantaneous non-dimensional spanwise vorticity patterns ω z D/U ∞ in the wake of the wired cylinder. Contour levels are |ω z |D/U ∞ = 0.4, 0.8, …, 4. Solid line (blue online) and dashed line (red online) contours indicate positive and negative vorticity, respectively.
Vortex trajectories and strengths of von Kármán vortices in the wake of a wired cylinder as a function of Reynolds number. (UT 1, UT 2: trajectories of upper vortices and LT 1, LT 2: trajectories of lower vortices.) Note that the upper vortices have a negative circulation value.
Vortex trajectories of von Kármán vortices at Re = 180 in the wake of a wired cylinder. Vortex trajectories are superposed on the instantaneous spanwise vorticity field at two instants which are T shed apart from each other. The corresponding trajectory of each vortex is shown with an arrow. Contour levels are |ω z |D/U ∞ = 0.4, 0.8, …, 4. Darker gray and lighter gray contours (blue and red, respectively, online) indicate positive and negative vorticity, respectively. The solid lines represent the contour line of λ2 = −0.1. (a) t = t 0; (b) t = t 0 + T shed .
Velocity vectors and streamwise vorticity patterns at the cross-stream plane of x/D = 4.5 at Re = 180. Contour levels of vorticity are |ω x |D/U ∞ = 0.2, 0.4, …, 2. and indicate secondary vortices with positive and negative circulation, respectively. λ z denotes the spanwise wavelength of the secondary vortices and is measured between the centers of vortices of the same sign.
Variation of strengths of secondary vortices Γ x /DU ∞ with Reynolds number Re and downstream position x/D in the near-wake.
Variation of spanwise wavelength of secondary vortices λ z /D with Reynolds number Re and downstream position x/D in the near-wake.
Variation of strength ratio Γ x /Γ z of secondary and primary vortices with Reynolds number Re and downstream position x/D in the near-wake.
Summary of PIV experiment details for side-view (XY -plane) and upstream-view (YZ -plane) wired cylinder measurements [Re = 180].
Maximum u rms /U ∞ values of the upper shear layer at different Reynolds numbers and percentage difference between wired and non-wired experiments.
Circulation values of von Kármán vortices at downstream position x/D = 10. Circulation values in the table are non-dimensionalized with 1/DU ∞.
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