CFD Online Discussion Forums

CFD Online Discussion Forums (
-   OpenFOAM Bugs (
-   -   Zero value for sigmayy (

seb62 January 20, 2009 12:03

Hi everyone, I am studying
Hi everyone,

I am studying 2D flow around a cylinder. Wind is coming along the x (horizontal) axis. Since I am interested in the drag and lift on the cylinder, I am extracting the pressure and viscous stresses on the cylinder, and computing lift and drag with the forceCoeffs functionObject.

I get viscous stress sigmayy around 10E-20 at any point of the cylinder, whereas sigmaxx and sigmaxy have significant values. To check if sigmayy should actually be zero, I decided to change the wind direction so that it is now along the y axis. I have again in this case significant values for sigmaxx and sigmaxy, and still zero values for sigmayy. The non-zero values for sigmaxx seems to confirm that sigmayy should not be zero.

Further integrating pressure forces and viscous stresses sigmaxx and sigmaxy over the cylinder, I can match the force along x given by forceCoeffs in both cases. However, I cannot match the force along y, which involves sigmaxy and sigmayy. The relative error is significant (around 25%).

simpleFoam, laminar case

UNIX 64 bit

OpenFOAM 1.5

Thanks for your answer,


henry January 20, 2009 13:09

There is a possibility that th
There is a possibility that this issue relates to problems with the symmTensor operators in 1.5 which have already been fixed in 1.5.x so it might be worth giving that a try. If you don't have any luck with 1.5.x could you please post the case here so we can look at the issue in more detail?


seb62 January 21, 2009 04:40

Thanks for the information, we
Thanks for the information, we are trying to install git and update to 1.5.x
I will post the results,


All times are GMT -4. The time now is 17:55.