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Vortex dynamics of a low aspect ratio cantilevered cylinder immersed in a boundary layer

Published online by Cambridge University Press:  25 August 2020

Samantha Gildersleeve  and
Michael Amitay Open the ORCID record for Michael Amitay [Opens in a new window]
Samantha Gildersleeve
Affiliation:
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY12180, USA
Michael Amitay*
Affiliation:
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY12180, USA
*
†Email address for correspondence: [email protected]
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Abstract

The flow physics associated with the interaction of a low aspect ratio, cantilevered cylindrical pin with a flow over a flat plate was investigated experimentally using oil visualizations and stereoscopic particle image velocimetry. The interactions of the vortical structures were explored for laminar, transitional and turbulent incoming boundary layers, where the flow's sensitivity to the pin's aspect ratio and its relative submergence within the boundary layer was studied. The surrounding flow is highly sensitive to subtle changes in these parameters (both are order 1) due to strong dependence between the flow over the pin's free end and its wake. These flow structures are heavily influenced by competing mechanisms of self-induction and shear flow due to outer fluid entrainment and the proximity to the wall. In particular, the observed vortical features exhibit strong inter-dependencies in the near wake. For a turbulent boundary layer, the resultant ‘arch-like’ structure is observed to be slightly stretched in the axial direction. Whereas, under laminar inflow conditions, the reduced shear and turbulence intensity facilitate a wider wake and a stronger downwash from the leeward edge, resulting in a concave ‘M-shaped’ vortex, affecting the formation and evolution of the trailing vortex pair. In addition, larger aspect ratios result in an increased magnitude of downwash into the wake, which re-energizes the near-wall flow. Whereas, for lower aspect ratios, the level of interaction between vortical features decreases due to a reduced downwash and weaker shear. These flow characteristics are discussed in detail in the paper.

JFM classification

Vortex Flows: Vortex dynamics Vortex Flows: Vortex interactions Wakes/Jets: Wakes
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 901 , 25 October 2020 , A18
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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Footnotes

‡

Present address: NASA Langley Research Center, Hampton, VA 23681-2199, USA.

References

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