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Reynolds number and slant angle effects on the flow over a slanted cylinder afterbody

Published online by Cambridge University Press:  21 April 2020

Fernando Zigunov Open the ORCID record for Fernando Zigunov [Opens in a new window] ,
Prabu Sellappan Open the ORCID record for Prabu Sellappan [Opens in a new window]  and
Farrukh Alvi
Fernando Zigunov*
Affiliation:
Department of Mechanical Engineering, FAMU-FSU College of Engineering,The Florida State University, Tallahassee, FL, USA
Prabu Sellappan
Affiliation:
Department of Mechanical Engineering, FAMU-FSU College of Engineering,The Florida State University, Tallahassee, FL, USA
Farrukh Alvi
Affiliation:
Department of Mechanical Engineering, FAMU-FSU College of Engineering,The Florida State University, Tallahassee, FL, USA
*
†Email address for correspondence: fzigunov@fsu.edu
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Abstract

The cylinder with a slanted base is a simplified, canonical bluff body geometry that shares similarities to aircraft fuselages, which are known to produce a strong vortex pair due to their upswept afterbody. This work will examine in detail the surface flow and near-field characteristics of the flow over the slanted cylinder for slant angles of $20^{\circ }$, $32^{\circ }$ and $45^{\circ }$ with spatially dense measurements. Principal flow features of the mean flow field are identified, showing the connection between the main counter-rotating vortex pair observed in the wake and the separation bubble observed at the leading edge of the slant. A full reconstruction of the three-dimensional mean flow field using stacked stereoscopic particle image velocimetry reveals intricate details of this flow and clearly shows the direct connection between the two features. To our knowledge, this is the first direct measurement of the full three-dimensional flow topology for this geometry. The separation bubble length is found to be directly proportional to the slant angle and inversely proportional to the Reynolds number. Furthermore, the circulation within the primary vortex pair increases with increasing slant angle. This strengthening of the vortices is correlated to the form drag of this body in the vortex-dominated regime. A bi-stable steady-state wake is also observed in this flow at a low Reynolds number for the slant angle of $45^{\circ }$, where the formation of either a separated wake flow state or a vortex-dominated flow state is dependent upon initial conditions, i.e. the presence of overshoot of the free-stream velocity during wind tunnel start-up.

JFM classification

Vortex Flows: Vortex interactions Wakes/Jets: Wakes
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 893 , 25 June 2020 , A11
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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Zigunov et al. supplementary movie 1

Time-lapse of surface oil flow development for ɸ=32º and ReD=5×105.

Download Zigunov et al. supplementary movie 1(Video)
Video 7.1 MB

Zigunov et al. supplementary movie 2

Time-lapse of surface oil flow development for ɸ=20º and ReD=5×105. Detail view highlights small reversed flow region inside separation bubble.

Download Zigunov et al. supplementary movie 2(Video)
Video 6.9 MB

Zigunov et al. supplementary movie 3

Time-lapse of surface oil flow development for ɸ=45º and ReD=5×105.

Download Zigunov et al. supplementary movie 3(Video)
Video 5 MB