Formation of a vortex street behind an oscillating cylinder

1995 ◽  
Vol 30 (1) ◽  
pp. 40-44 ◽  
Author(s):  
Ya. D. Afanasyev ◽  
I. A. Filippov
Keyword(s):  
Vortex Street ◽  
Oscillating Cylinder

Effect of Channel Inlet Blockage on the Wake Structure of a Rotationally Oscillating Cylinder

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
S. Kumar
Keyword(s):  
Mode Shape ◽  
Channel Wall ◽  
Shape Change ◽  
Vortex Street ◽  
Channel Width ◽  
Channel Inlet ◽  
Oscillating Cylinder ◽  
Wake Structure ◽  
Freestream Velocity ◽  
Cylinder Diameter

This paper investigates, experimentally for the first time, the effect of channel inlet blockage induced by bringing the channel inlet walls closer together on the wake structure of a rotationally oscillating cylinder. The cylinder is placed symmetrically inside the channel inlet. The Reynolds number (based on constant upstream channel inlet freestream velocity) is 185, and three channel wall spacings of two, four, and eight cylinder diameters are used. Cylinder oscillation amplitudes vary from π/8 to π, and normalized forcing frequencies vary from 0 to 5. The diagnostics is done using hydrogen-bubble flow visualization, hot-wire anemometry, and particle image velocimetry (PIV). It is found that rotational oscillations induce inverted-vortex-street formation at channel width of two cylinder diameter where there is no shedding in unforced case. The channel wall boundary layers at this spacing undergo vortex-induced instability due to vortex shedding from cylinders and influence the mechanism of inverted-vortex-street formation near the cylinder. At channel width of four cylinder diameter, the inverted-vortex-street is still present but the mode shape change seen at normalized forcing frequency of 1.0 in the absence of channel walls is delayed due to the presence of nearby walls. The wake structure is observed to resemble the wake structure in unbounded domain case at channel width of eight cylinder diameter with some effect of channel walls on forcing parameters where mode shape change occurs. The lock-on diagram is influenced by the closeness of the channel walls, with low-frequency boundary moving to lower frequencies at smallest channel width.

Flow past a rotationally oscillating cylinder with an attached flexible filament

2021 ◽  
Vol 930 ◽  
Author(s):  
Puja Sunil ◽  
Sanjay Kumar ◽  
Kamal Poddar
Keyword(s):  
Control Volume ◽  
Transverse Velocity ◽  
Experimental Studies ◽  
Vortex Street ◽  
Oscillating Cylinder ◽  
Karman Vortex Street ◽  
Flexible Filament ◽  
Flow Past ◽  
Kármán Vortex Street ◽  
Karman Vortex

Experimental studies are conducted on a rotationally oscillating cylinder with an attached flexible filament at a Reynolds number of 150. Parametric studies are carried out to investigate the effect of cylinder forcing parameters and filament stiffness on the resultant wake structure. The diagnostics are flow visualization using the laser-induced fluorescence technique, frequency measurement using a hot film, and characterization of the velocity and vorticity field using planar particle image velocimetry. The streamwise force and power are estimated through control volume analysis, using a modified formulation, which considers the streamwise and transverse velocity fluctuations in the wake. These terms become important in a flow field where asymmetric wakes are observed. An attached filament significantly modifies the flow past a rotationally oscillating cylinder from a Bénard–Kármán vortex street to a reverse Bénard–Kármán vortex street, albeit over a certain range of Strouhal number, $St_{A} \sim 0.25\text {--}0.5$ , encountered in nature in flapping flight/fish locomotion and in the flow past pitching airfoils. The transition from a Kármán vortex street to a reverse Kármán vortex street precedes the drag-to-thrust transition. The mechanism of unsteady thrust generation is discussed. Maximum thrust is generated at the instants when vortices are shed in the wake from the filament tip. At $St_{A} > 0.4$ , a deflected wake associated with the shedding of an asymmetric vortex street is observed. Filament flexibility delays the formation of an asymmetric wake. Wake symmetry is governed by the time instant at which a vortex pair is shed in the wake from the filament tip.

Formation of Vortex Street in Laminar Boundary Layer

1980 ◽  
Vol 47 (2) ◽  
pp. 227-233 ◽  
Author(s):  
M. Kiya ◽  
M. Arie
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
Laminar Boundary Layer ◽  
Solid Wall ◽  
Vortex Sheet ◽  
Vortex Street ◽  
Bluff Bodies ◽  
Uniform Shear ◽  
Uniform Shear Flow ◽  
Vortex Patterns

Main features of the formation of vortex street from free shear layers emanating from two-dimensional bluff bodies placed in uniform shear flow which is a model of a laminar boundary layer along a solid wall. This problem is concerned with the mechanism governing transition induced by small bluff bodies suspended in a laminar boundary layer. Calculations show that the background vorticity of shear flow promotes the rolling up of the vortex sheet of the same sign whereas it decelerates that of the vortex sheet of the opposite sign. The steady configuration of the conventional Karman vortex street is not possible in shear flow. Theoretical vortex patterns are experimentally examined by a flow-visualization technique.

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