From 31e092b0bf2d984f2b150049e563031deb0d83df Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Wed, 7 Oct 2009 15:52:38 +0000 Subject: [PATCH] A few more figures from the Re=500 computation. git-svn-id: https://svn.dealii.org/trunk@19751 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/examples/step-35/doc/results.dox | 40 +++++++++++++++++++----- 1 file changed, 33 insertions(+), 7 deletions(-) diff --git a/deal.II/examples/step-35/doc/results.dox b/deal.II/examples/step-35/doc/results.dox index 25bb7c7598..03f30d81e9 100644 --- a/deal.II/examples/step-35/doc/results.dox +++ b/deal.II/examples/step-35/doc/results.dox @@ -92,13 +92,39 @@ whether this is a left or right turning vortex.

Re = 500

-Changing the Reynolds number, $Re$, to in the parameter file to a value of $500$ we obtain the following results. -@image html Re500t0.png -@image html Re500t1.png -@image html Re500t3.png -@image html Re500t5.png -@image html Re500t8.png -@image html Re500t10.png +We can change the Reynolds number, $Re$, in the parameter file to a +value of $500$. Doing so, and reducing the time step somewhat as well, +yields the following images at times $t=20,40: + + + + + + + + + + +
@image html step-35.Re_500.vorticity.0.png @image html step-35.Re_500.velocity.0.png
@image html step-35.Re_500.vorticity.1.png @image html step-35.Re_500.velocity.1.png
+ +What does look right is that with the higher Reynolds number, the flow +is much more unorganized, swaying between the bottom and top boundary +of the domain. On the other hand, the vorticity can't be right: it +oscillates rapidly, not something we would expect for a Reynolds +number that is still only moderate and that would not produce +turbulence at very small length scales. The riddle is easily solved, +however, by looking at a zoom at the region behind the obstacle, and +the mesh size we have there: + +@image html step-35.Re_500.zoom.png + +It is clear here that the flow is still reasonably well resolved in +the immediate wake of the obstacle, where the mesh is relatively fine, +but that the problem appears where the mesh becomes too coarse. That +shouldn't surprise us: if we increase the Reynolds number, the scales +on which we expect flow variation decreases and we will have to have a +finer mesh. A rerun with one more mesh refinement dialed in in the +parameter file confirms that results look much more sensible now. -- 2.39.5