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Weakly sheared turbulent flows generated by multiscale inhomogeneous grids

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2018 JFM shear grid paper - pre print version.pdfAccepted version1.38 MBAdobe PDFView/Open
Title: Weakly sheared turbulent flows generated by multiscale inhomogeneous grids
Authors: Zheng, S
Bruce, PJK
Graham, JMR
Vassilicos, JC
Item Type: Journal Article
Abstract: A group of three multiscale inhomogeneous grids have been tested to generate different types of turbulent shear flows with different mean shear rate and turbulence intensity profiles. Cross hot-wire measurements were taken in a wind tunnel with Reynolds number ReD of 6000–20 000, based on the width of the vertical bars of the grid and the incoming flow velocity. The effect of local drag coefficient CD on the mean velocity profile is discussed first, and then by modifying the vertical bars to obtain a uniform aspect ratio the mean velocity profile is shown to be predictable using the local blockage ratio profile. It is also shown that, at a streamwise location x = xm, the turbulence intensity profile along the vertical direction u0(y) scales with the wake interaction length x peak ∗,n = 0.21g2n/(αCDwn) (α is a constant characterizing the incoming flow condition, and gn, wn are the gap and width of the vertical bars, respectively, at layer n) such that (u0/Un) 2β2 (CDwn/x peak ∗,n) −1 ∼ (xm/x peak ∗,n) b, where β is a constant determined by the free-stream turbulence level, Un is the local mean velocity and b is a dimensionless power law constant. A general framework of grid design method based on these scalings is proposed and discussed. From the evolution of the shear stress coefficient ρ(x), integral length scale L(x) and the dissipation coefficient C (x), a simple turbulent kinetic energy model is proposed that describes the evolution of our grid generated turbulence field using one centreline measurement and one vertical profile of u 0 (y) at the beginning of the evolution. The results calculated from our model agree well with our measurements in the streamwise extent up to x/H ≈ 2.5, where H is the height of the grid, suggesting that it might be possible to design some shear flows with desired mean velocity and turbulence intensity profiles by designing the geometry of a passive grid.
Issue Date: 10-Aug-2018
Date of Acceptance: 1-Jun-2018
URI: http://hdl.handle.net/10044/1/77639
DOI: 10.1017/jfm.2018.387
ISSN: 0022-1120
Publisher: Cambridge University Press (CUP)
Start Page: 788
End Page: 820
Journal / Book Title: Journal of Fluid Mechanics
Volume: 848
Copyright Statement: © 2018 Cambridge University Press. This paper has been accepted for publication and will appear in a revised form, subsequent to peer-review and/or editorial input by Cambridge University Press.
Sponsor/Funder: Commission of the European Communities
Commission of the European Communities
Funder's Grant Number: FP7 - 317269
320560
Keywords: Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
turbulent flows
SMALL-SCALE STRUCTURE
PLANE COUETTE-FLOW
UNIFORM SHEAR
WIND-TUNNEL
ISOTROPIC TURBULENCE
VELOCITY PROFILES
GAUZE SCREENS
STEADY FLOW
DECAY
FIELD
Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
turbulent flows
SMALL-SCALE STRUCTURE
PLANE COUETTE-FLOW
UNIFORM SHEAR
WIND-TUNNEL
ISOTROPIC TURBULENCE
VELOCITY PROFILES
GAUZE SCREENS
STEADY FLOW
DECAY
FIELD
Fluids & Plasmas
01 Mathematical Sciences
09 Engineering
Publication Status: Published
Open Access location: https://doi.org/10.1017/jfm.2018.387
Online Publication Date: 2018-06-13
Appears in Collections:Aeronautics