Strange Results With snappyHexMesh
 

Hello Foamers,

Before beginning let me apologize that my supporting material is rather incomplete and far from rigorous. I have been trying to model a flapping ellipse shaped airfoil, but the forces calculated by OpenFoam differ wildly from those calculated using COMSOL. I then tried to simulate a cylinder oscillating transversely to the free stream fluid flow but again my results with OpenFoam differ substantially, orders of magnitude, from the results presented in Blackburn 98, in the Journal of Fluid Mechanics.

After several weeks of struggle, I now believe that my problems are related to the use of snappyHexMesh to produce my computational domain. I further restricted myself to the almost trivial case of flow past a fixed cylinder, and using the mesh from the tutorial I obtain reasonable results for the lift and drag coefficients, order unity, at my Reynolds number of 500 which I realize is a bit too high to draw definitive conclusions since the wake could be turbulent and therefore unsymmetrical so the use of a symmetry plane is dubious. I created a second case using snappyHexMesh to generate a mesh around a full cylinder with, I believe, similar boundary conditions, however, when I run this second case the calculated lift and drag coefficients are drastically lower than on the mesh generated with blockMesh.

It is entirely possible that I am doing something silly with snappyHexMesh. I use extrudeMesh and autoPatch to create a two dimensional mesh from the mesh generated by snappyHexMesh, but I have no confidence that I used appropriate settings for snappyHexMesh. Additionally, I have turned on non-orthogonal correction for the icoeFoam solver which I used for both cases. I have included the two differing cases. I actually used a slightly modified version of icoFoam that utilizes adjustable time stepping, but my results where similar using the standard version of icoFoam. I have also included the 3D and 2D case directories for the mesh generation using snappyHexMesh. Sorry in advance for the messiness of my case files.

http://dl.dropbox.com/u/21019547/ful...HexMesh.tar.gz
http://dl.dropbox.com/u/21019547/hal...ockMesh.tar.gz
http://dl.dropbox.com/u/21019547/sna..._circle.tar.gz
http://dl.dropbox.com/u/21019547/sna..._circle.tar.gz

Any help is greatly appreciated.

Caleb