BREAKDOWN AND REARRANGEMENT OF A VORTEX STREET IN THE FAR WAKE OF A CYLINDER

Breakdown and rearrangement of a primary vortex street shed from a circular cylinder in the far wake are experimentally examined for 70<R<154 (R is the Reynolds number based on the diameter of the cylinder). According to the vorticity fields obtained using digital image processing for visualized flow fields, the primary vortex street breaks down into a nearly parallel shear flow of Gausian profile at a certain downstream distance, before a secondary vortex street of larger scale appears further downstream. The process leading to the nearly parallel flow can be explained as the evolution of the vortex regions of an inviscid fluid if the observation is evoked that the distance between the two rows in the primary vortex street increases with the downstream distance. Numerical computations with the discrete vortex method also support this explanation. Next, the wavelengths a1 and a2, of the primary and secondary vortex streets are calculated from the above vorticity fields, and are also measured from the flow patterns obtained using the aluminium dust method. The ratio a2/a1 decreases with increasing R, and ranges from 1.7 to 2.6. Moreover, the wavelength a2 is a little smaller than that of the most unstable mode in the linear stability theory applied to the above nearly parallel flow. The speeds of the vortex streets relative to the fluid at infinity are also measured, and are 0.12U-0.19U and 0.03U- 0.10U for the primary and secondary ones, respectively. Here U is the speed of the cylinder.

• Supplemental Notes:
  • Res Inst Appl Mechs Rpts, v 39 n 110, Feb 1994, p 1 [27 p, 31 ref, 1 tab, 16 fig]
• Authors:
  • Karasundani, T
  • Funakoshi, M
• Publication Date: 1994

Language

• English

Subject/Index Terms

• TRT Terms: Cylindrical bodies; Image processing; Vortex shedding; Wakes
• Subject Areas: Marine Transportation; Materials;

Filing Info

• Accession Number: 00708215
• Record Type: Publication
• Source Agency: British Maritime Technology
• Files: TRIS
• Created Date: Aug 14 1995 12:00AM