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Round Table, Wednesday 28 Chairman: Z.Warhaft

Round Table, Wednesday 28 Chairman: Z.Warhaft. Few notes :. Slide 2 . John Lumley told me he wrote this. Slide 4. Right hand graph shows the lack of precision of pre-factors in Lagrangian measurements (in this case a_0). We need to know these with more precision.

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Round Table, Wednesday 28 Chairman: Z.Warhaft

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  1. Round Table, Wednesday 28Chairman: Z.Warhaft Few notes: • Slide 2. John Lumley told me he wrote this. • Slide 4. Right hand graph shows the lack of precision of pre-factors in Lagrangian measurements (in this case a_0). We need to know these with more precision. • Slide 5. Lack of inertial subrange in Lagrangian measurements means we have to measure to very, very high Re. • Slide 6. We need to measure Lagrangian statistics in more complex flows. Here are measurements in a boundary layer. • Slide 7. And we need to understand about the interaction of two or more dominant scales (as you know well!). Here is the interaction of free stream turbulence (low wave number peak) and a turbulent boundary layer (high wave number peak). • Slide 8. As for 6. Flow through a contraction produces two scales. Here the effect only becomes clear at high Re. So we need to look at these more complex flows at high Re.

  2. We believe that even after 100 years, turbulence studies are still in their infancy. We are naturalists, observing butterflies in the wild. We are still discovering how turbulence behaves, in many respects. We do have a crude , practical, working understanding of many turbulence phenomena but certainly nothing approaching a comprehensive theory, and nothing that will provide predictions of an accuracy demanded by designers. (from J.L.Lumley and A.M.Yaglom. Flow,Turbulence and Combustion, 66: 241, 2001)

  3. Some issues of interest: Large Reynolds numbers: Lagrangian experiments. Study of variable constants !! Out of the box: advanced diagnostics for complex flows: interaction of more than one length scale. Passive scalar---non universality of structure fn. exponents (Gylfason & W, PoF 2004, Mydlarski, PRL, 2009.) She et al. 1991 Ishihara, Gotoh, Kaneda, 2009

  4. Fluid particles: Lagrangian measurements Acceleration variance, From Tsinober et al, 2007 Bodenschatz accelertion pdf’s See also Pinton

  5. Ouellette et al. NJP 2006 No

  6. The mean acceleration as a function of y+ Squares: St=0.47, Re=240 Circles:St=0.07;St=240 Triangles:St=0.035,Re=100 Open symbols--experiment Filled symbols--model Boundary layer with free stream turbulence. Geraschenko et al. JFM 2008

  7. Spectra normal-ized by inner variables See also Marusic & co-workers Boundary layer with free stream turbulence. Sharp et al. PoF 2009

  8. Flow through as contraction: Re effects

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