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Numerical investigation of free-stream turbulence effects on the transition-in-wake state of flow past a circular cylinder

Abstract

We investigate how a turbulent free-stream (TFS) affects the transition-in-wake state of flow past a cylinder. Direct numerical simulations of a decaying TFS flow past a cylinder have been performed, where the intensity and integral scale of the TFS was varied. Distinct effects of the TFS are observed for Reynolds numbers in the lower (Re < 190) and upper (Re ≥ 250) ranges of the transitional regime. For a flow with a laminar free-stream (LFS), the onset of the transition-in-wake is observed at critical Reynolds number 190, where the first three-dimensional effects develop in the wake (mode A instabilities). A TFS perturbs the flow, forcing the onset of the transition at a lower Reynolds number and inhibiting a sharply defined critical Reynolds number. Quasi-stable states, where the wake alternates between two- and three-dimensional vortex shedding, are observed for Re < 190. These states are closely related to intermittent vortex dislocations in the wake. In the upper Re part of the transition-in-wake regime, mode B instabilities dominate the wake of the LFS flow. A TFS stimulates the existence of mode A instabilities, resulting in mixed A–B instabilities in the wake for Re ≥ 250. This effect correlates with the turbulence intensity. © 2018 Informa UK Limited, trading as Taylor & Francis Group.
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Category

Academic article

Client

  • Research Council of Norway (RCN) / 231444
  • Sigma2 / NN2649K
  • Sigma2 / NS2649K

Language

English

Author(s)

Affiliation

  • Norwegian University of Science and Technology
  • SINTEF Energy Research / Termisk energi

Year

2018

Published in

Journal of turbulence

ISSN

1468-5248

Volume

19

Issue

3

Page(s)

252 - 273

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