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Influence of the bluff body shear layers on the wake of a square prism in a turbulent flow

D. C. Lander and C. W. Letchford

M. Amitay

G. A. Kopp

  • Department of Civil & Environmental Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA

  • Center for Flow Physics & Control, Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA

  • Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, London, Ontario, Canada N6A 5B9

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Phys. Rev. Fluids 1, 044406 – Published 9 August, 2016

DOI: https://doi.org/10.1103/PhysRevFluids.1.044406

Abstract

Despite a substantial body of literature dealing with the effects of free-stream turbulence (FST) on two-dimensional square prism, there remain some open questions regarding the influence of the bluff body shear layer development in a highly perturbed environment and the resulting impact on bluff body flow characteristics. Accordingly, flows with ambient and enhanced FST were studied at ReD=5.0×104 using long-duration time-resolved particle image velocimetry (PIV). The data indicate a narrowing and lengthening of the mean wake and an accompanying rise in base pressure. Using triple decomposition, the underlying dynamics of the wake reveal a streamwise lengthening of the individual von Kármán vortex structures, complementing the increase in mean wake length. Close inspection of the shear layer region, in the presence of FST, indicates a substantial increase in curvature towards the body but no pronounced increase in the growth rate. The loci of maximum turbulent kinetic energy and spanwise vorticity in the shear layer region further reveal that the most pronounced changes occur during the very initial stages follow separation. Inspection of a series of instantaneous PIV fields of Q criterion show that the conventional transition pathway, via the formation and subsequent pairing of the Kelvin-Helmholtz (KH) vortices, is bypassed. The KH vortices are observed to immediately cluster and amalgamate before breaking into smaller random eddies. The bypass transition is followed by shear layer reattachment in some cases. This is considered a primary mechanism responsible for the reported changes in the global flow characteristics and the altered wake dynamics. Furthermore, a quantitative definition of the diffusion length is implemented for the square prism wake and its relationship to the Strouhal number and wake formation length is considered.

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Phys. Rev. Fluids 1, 044406– Published 9 August, 2016
  • Received 20 January 2016
Article part of CHORUS

©2016 American Physical Society

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