gtspring2009
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gtspring2009 [2011/08/04 08:07] predrag Woods Hole report |
gtspring2009 [2011/08/04 12:33] predrag added two movies with zillion hairpins, the first one wrong |
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| - | {{gtspring2009:pc.jpg }} Woods Hole GFD snippets: Listening to [[http://www.mech.kth.se/~henning/|Dan Hennignson]]: watching their movies of the boundary layer is very fascinating - if you find them on their homepage, please put a link here. Used 5000 processors for 6 months; amounts to 40 cm of Boing 747. Wu & Moin recent work claims that the initial forest of hairpin vortices. Not correct. They do not look at as high Reynolds numbers. They do not get the averages right. Henningson results are much better, and the transition region does not persist. For plane Couette, 800 1/2 heights domain, showed a movie that shows that initial noisy conditions go into stripes. That justifies using smaller cells. | + | {{gtspring2009:pc.jpg }} Woods Hole GFD snippets: Listening to [[http://www.mech.kth.se/~henning/|Dan Hennignson]]: watching their [[http://www.youtube.com/watch?v=4KeaAhVoPIw|movies of the boundary layer]] is very fascinating - if you find them on their homepage, please put a link here. Used 5000 processors for 6 months; amounts to 40 cm of Boing 747. Wu & Moin recent work claims that the [[http://www.youtube.com/watch?v=GW2LRo2ZigQ|initial forest of hairpin vortices survives]]. Not correct. They do not look at as high Reynolds numbers. They do not get the averages right. Henningson results are much better, and the transition region does not persist. For plane Couette, 800 1/2 heights domain, showed a movie that shows that initial noisy conditions go into stripes. That justifies using smaller cells. |
| Study this: They use Lagrange multipliers method to get to the adjoint Navier-Stokes evolution (this might be the way to deal with Domenico's noise evolution for hyperbolic fixed points, as well). Dan finds it remarkable that it works in optimized perturbation settings. This was discussed in detail in the talk "Questioning the question: The role of nonlinear optimal perturbations in the transition to turbulence of plane Couette flow" by [[http://www.damtp.cam.ac.uk/people/c.p.caulfield/|Colm-cille Caulfield]]. ([[http://en.wikipedia.org/wiki/Columba|Colm-cille]] is an Irish name). Concerning finite amplitude perturbations for plane Couette transition from laminar to optimal (Monokrousos et al (2011)): For dissipation norm, with the same energy disturbance, //localized// disturbances are optimal (but not too localized - would be interesting to understand the scale). Numerical observations support this - the point where transition happens are localized. He showed a few movies where localized -> vortex pair -> streak, grow due lift-up effect -> and pretty turbulent looking edge state. It is the Orr mechanism of generating a 2D packet (the strongest transient growth mechanism in 2D, a version of Kelvin circulation theorem), but it is essential that disturbance is 3D, or Orr mechanism would make the perturbation die away. --- //[[predrag.cvitanovic@physics.gatech.edu|Predrag Cvitanovic]] 2011/08/04 07:12// | Study this: They use Lagrange multipliers method to get to the adjoint Navier-Stokes evolution (this might be the way to deal with Domenico's noise evolution for hyperbolic fixed points, as well). Dan finds it remarkable that it works in optimized perturbation settings. This was discussed in detail in the talk "Questioning the question: The role of nonlinear optimal perturbations in the transition to turbulence of plane Couette flow" by [[http://www.damtp.cam.ac.uk/people/c.p.caulfield/|Colm-cille Caulfield]]. ([[http://en.wikipedia.org/wiki/Columba|Colm-cille]] is an Irish name). Concerning finite amplitude perturbations for plane Couette transition from laminar to optimal (Monokrousos et al (2011)): For dissipation norm, with the same energy disturbance, //localized// disturbances are optimal (but not too localized - would be interesting to understand the scale). Numerical observations support this - the point where transition happens are localized. He showed a few movies where localized -> vortex pair -> streak, grow due lift-up effect -> and pretty turbulent looking edge state. It is the Orr mechanism of generating a 2D packet (the strongest transient growth mechanism in 2D, a version of Kelvin circulation theorem), but it is essential that disturbance is 3D, or Orr mechanism would make the perturbation die away. --- //[[predrag.cvitanovic@physics.gatech.edu|Predrag Cvitanovic]] 2011/08/04 07:12// | ||
gtspring2009.txt ยท Last modified: 2011/08/10 08:11 by predrag
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