UNSTEADY DETACHED SEPARATION FROM A CIRCULAR CYLINDER PERFORMING ROTATIONAL OSCILLATIONS IN A UNIFORM VISCOUS INCOMPRESSIBLE FLOW
✍ Scribed by M. N. Zakharenkov
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 172 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0271-2091
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✦ Synopsis
The origination of detached separation is studied on the basis of a numerical solution of the full Navier±Stokes equations. Fluxes of vorticity with different signs generated with twice the frequency of cylinder oscillation move from the cylinder to the outer surface of a detached liquid layer in the form of concentric rings. Near the critical layer between the attached layer and the main ¯ow these rings are torn and crimped to the regions of separated vortices of the corresponding sign. The form of detached separated vortices is similar to that of vortices originating from a stationary circular cylinder in a uniform ¯ow. Transition of the ¯ow to a non-symmetric form with Karman vortex street generation at a Reynolds number (based on the radius) greater than 17 is revealed. This critical Reynolds number is smaller than that for a stationary circular cylinder in a viscous stream (where Re 20 has been determined to be a critical value) and corresponds to the Reynolds number extrapolated from the critical value for the stationary cylinder by increasing the cylinder radius by the attached layer thickness. The vorticity ¯ux from the cylinder surface immediately into the separation region decreases as the frequency of cylinder oscillation increases. Violation of the ¯ow potentiality in the detached separation region is the main cause of the vorticity generation on the outer surface of the attached liquid layer.