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Wake Behind a Cylinder: An Overview of Spatio-Temporal Aspects
Uruba, Václav
A circular cylinder in crossflow is subjected to the overview study from the point of view spatial and temporal characteristics. It represents itself a typical engineering problem, appearing in practice frequently in various forms. In fluid mechanics, this case is considered to be a typical canonical case, with relatively simple and straightforward definition, but complex and dynamical flow topology. The typical dynamics is characterized by quasi-periodic behavior called von Kármán – Bénard vortex street with a typical frequency expressed in dimensionless number called Strouhal number. The wake flow structure is considered to be characterized by a single frequency and 2D topology, homogeneous along the cylinder axis, very often. The presented paper concentrates on differences between this commonly accepted model and physical reality. Both temporal and spatial aspects of the flow in the wake behind a cylinder are to be addressed. The turbulent subcritical wake characterized by Reynolds number about 5 thousand will be considered, as this situation is a typical case in mechanical engineering applications.
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On Harmonic Content of the Wake Behind a Circular Cylinder
Uruba, Václav ; Procházka, Pavel P.
The wake behind cylinder of circular cross-section is subjected to detailed analysis from the point of view harmonic content. The basic, fundamental frequency could be linked to well-known Bénard-von Kámán vortex street, it is called Strouhal frequency very often. However higher harmonics of 2nd and 3rd order have been detected, as well as important inharmonic partials. The topologies of the velocity flow-field corresponding to the harmonic is to be shown.
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On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav ; Procházka, Pavel P. ; Skála, Vladislav
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of statistic quantities along the cylinder is uniform, and i.e. 2D, the instantaneous flow structure is fully 3D. Within the velocity fluctuating flow field the structures containing streamwise vorticity and velocity components are dominant. The POD modes connected with von Kármán vortex street are identified.
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