turbulent boundary layer structure - university of...
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From www.cortana.com
Turbulent boundary layer structure
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Shear velocity, u*u* = √τo/ρ
0 hR Sτ γ=
= cross-sectional area/wetted perimeter
Shear velocity, u*u* = √τo/ρ
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Turbulent boundary layer structure over a FLAT bed
Classic research by the groups of Kline (Stanford) and Grass (UCL)
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Tony Grass (UCL)JFM 1971
Used H2 bubbles over different bed roughness
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Burst and sweeps
Grass, 1971
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+U’-U’
+v’
-v’
If U’ and v’ are deviation of downstream and vertical velocity from their mean (+ve v = upwards)
12
3 4
2 = bursts4 = sweeps1 = outward interactions3 = inward interactions
Define a ‘hole’ size to exclude small
events Quadrant Analysis
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Tb=fU/Y~5
Jackson, 1975, 1976
Burst period
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Smith and Metzler, 1983
Planform characteristics…Smith and Metzler, 1983
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Smith and Metzler, 1983
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H2 bubblewire
low-speedstreaks
flow
time
Looking down onto the channel bed
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Low speed streak spacing, λ+:
λ+ = λ.u*/ν
where λ = streak spacingu* = shear velocity
ν = kinematic viscosity
λ+ = λ.u*/ν ≅ 100
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Smith and Metzler, 1983
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Smith and Metzler, 1983
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Smith and Metzler, 1983
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Smith and Metzler, 1983
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The burst-sweep cycle (from Allen, 1984) - hairpins
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The earlier work of Kline and
colleagues
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Smith et al., 1991
Generation of secondary hairpin vortices (Smith et al., 1991)
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Turbulent Boundary Layer Structure (Robinson, 1991)
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Robinson, 1991
Turbulent Boundary Layer Structure (Robinson, 1991)
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Wall-attached hairpin
Adrian et al., 2000
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Adrian, 2007
More complex packets of vortices
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Adrian, 2007
A model of vortex packets
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Spanwise merger of hairpins by vortex reconnection of legs
Adrian, 2007
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Adrian, 2007
Movie 1
Movie 2
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transitions to turbulence
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Links to Large-Scale-Motions (Falco, 1977)
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streaks
entrainment patch
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movie
Adrian, 2007
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Long streaks of low-momentum fluid in streamwise-spanwise planes of boundary layer flow at y/δ = 0.2 and Reθ = 2216. The red (blue) contours represent regions of swirling strength.
Adrian, 2007
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Summary sketch of the organization of hairpins and packets in a boundary layer.
Adrian, 2007
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References***Adrian, R.L. (2007) Hairpin vortex organization in wall turbulence, Physics of Fluids, 19, 041301.****Marusic, I. (2009) Unravelling turbulence near walls, Journal of Fluid Mechanics, 630, 1-4.*
Grass, A.J. (1971) Structural features of turbulent flow over smooth & rough boundaries, J. Fluid Mechanics, 50, 233-255.Kline, S. J., Reynolds, W. C., Schraub, F. A. & Runstadler, P. W. (1967) The structure of turbulent boundary layers. Journal of Fluid Mechanics, 30, 741-773. Robinson, S. K. (1991) Coherent motion in the turbulent boundary layer. Ann. Rev. Fluid Mech. 3, 601-639.Smith, C.R. and Metzler, S.P. (1983) The characteristics of low-speed streaks in the near-wall region of a turbulent boundary layer, Journal of Fluid Mechanics, 129, 27-54.Smith, C.R. (1996), Coherent flow structures in smooth-wall turbulent boundary layers: Facts, mechanisms and speculation. in Coherent Flow Structures in open channels edited by P.J. Ashworth, S.J. Bennett, J.L. Best, and S.J. McLelland, pp. 1-39, John Wiley and Sons.
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Next weeks seminars
Alex: Head, M.R., and P. Bandyopadhyay (1981), New aspects of turbulent boundary layer structure, Journal of Fluid Mechanics, 107, 297-338.Justin: Adrian, R. J., C. D. Meinhart and C. D. Tomkins (2000), Vortex organization in the outer region of the turbulent boundary layer, Journal of Fluid Mechanics, 422, 1-54. Ron: 2 papers in Science!Marusic et al., (2010) Predictive model for wall-bounded turbulent flow, Science, 329, 9 July 2010.Adrian, R.J. (2010) Closing in on models of wall turbulence, Science, 329, 9 July 2010.
NOTE: These can be large papers!: start with Intro, Conclusions and Discussion: reviewers can then focus in on
papers