Issues with OpenFoam
 

Hi,

I am new to OpenFoam, however have been using FLUENT for a long time. To start a new project in OpenFoam, I thought it might be good to compare a benchmark case between OpenFoam and FLUENT. So, I took turbulent flow over a BACKWARD FACING STEP. Following are my conclusions:

1) Substantial difference in the velocity, turbulent-kinetic-energy and turbulent-dissipation fields.

2) The reattachment length is shorter in OPENFOAM prediction; While there are two circulation zones, top and bottom of the jet, predicted by OPENFOAM, there is only one predicted by FLUENT, the bottom one.

3) While I can use higher order discretization schemes in FLUENT, in OpenFoam I can use only "upwind" which is a first-order, bounded scheme. When I used 2nd order schemes, the results showed instability and no convergence was achieved. Does this mean we have to use only "upwind" and cannot use the higher order schemes ?

4) I also wanted to test the linear solvers by replacing default PCG/PBiCG with GAMG. However, this did not work and the simulation stopped abruptly. Does this mean we can use only PCG/PBiCG ?

These are critical to my project and would help immensely to understand how OpenFoam works.

Regards,

Sanjib