Advertisement

Experiments in Fluids

, Volume 33, Issue 1, pp 54–65 | Cite as

Control of vortex formation from a vertical cylinder in shallow water: Effect of localized roughness elements

  •  A. Kahraman
  •  B. Sahin
  •  D. Rockwell

Abstract.

Vortex formation from a vertical cylinder in shallow water is controlled by placement of a narrow transverse strip of roughness elements on the bed (bottom surface). A technique of high-image-density particle image velocimetry is employed to obtain global, instantaneous representations of the flow patterns, which lead to phase- and time-averaged patterns of streamline topology and Reynolds stress on planes at and above the bed. Near the bed, the overall form of the streamline topology is maintained, even at larger heights of the roughness elements. With increasing height of the elements, the downstream saddle point is further displaced in the streamwise direction. Correspondingly, the streamwise extent of the negative pocket of the streamwise velocity component, i.e., the region of reverse flow along the bed surface, increases substantially in the streamwise direction. The Reynolds stress in the very near-wake, at locations upstream of the roughness elements, is significantly attenuated, even for small height of roughness. This attenuation occurs not only near the bed surface, but also at the midplane of the shallow water wake, and thereby indicates that the consequence of localized roughness is to exert a global influence. In fact, corresponding patterns of instantaneous velocity and vorticity indicate that consistent formation of large-scale vortices in the very near-wake region is attenuated with relatively small surface roughness on the bed. Downstream of the roughness elements, the patterns of Reynolds stress near the bed surface, as well as at the midplane of the water layer, are significantly altered relative to the case of no roughness. Near the bed, highly concentrated patterns of positive and negative Reynolds stress in the absence of roughness give way to lower-level regions of Reynolds stress in the form of alternating concentrations; the particular pattern depends on the height of the roughness elements. At the midplane of the water layer, the Reynolds stress patterns maintain their same overall form, but the extrema of the Reynolds stress concentrations are attenuated in magnitude and are shifted in the downstream direction, with increasing height of the roughness elements. These observations are complemented by patterns of instantaneous velocity and vorticity.

Keywords

Vorticity Particle Image Velocimetry Reynolds Stress Instantaneous Velocity Streamwise Direction 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  •  A. Kahraman
    • 1
  •  B. Sahin
    • 1
  •  D. Rockwell
    • 2
  1. 1.Department of Mechanical Engineering, Cukurova University, Balcali 01330 Adana, Turkey
  2. 2.Department of Mechanical Engineering and Mechanics, 354 Packard Laboratory, 19 Memorial Drive West, Lehigh University, Bethlehem, PA 18015, USA

Personalised recommendations