[chenu]

Hello,
Does anyone know how force function object works?
In my case, I use openFOAM only for mesh generation and post-process. Flow field is solved by my own flow solver, which is compiled to object and imported in OpenFOAM.
If I solve flow field by my own flow solver and set end time 15 seconds, I will have drag coeff. 1.5. However, if I run flow solver again from 15s(either my flow solver or OpenFOAM solver), the drag force is 6.8. I have tried to create a new OF solver, which reads fluid properties from 15 seconds and output force, the drag coefficient is also 6.8, no 1.5

I will appreciate for any suggestion or pointing out any procedure that I missed, thank you.

[geth03]

every force at a patch is calculated by integrating pressure and viscous shear stress.

[chenu]

Hello geth03,
I know that force is calculated by integrating pressure and viscous force on the surface. My question is, I have created a solver in OpenFOAM, the flow field is solved by calling my own function instead of OpenFOAM such as UEqn.solve() and Peqn.solver(). The flow field is consistent with the result from icoFOAM, but the force is always wrong. Once I restart my solver and set the last time step data as initial condition, the force matches icoFoam.
Thank you for your reply.

[SaddamH]

Hello, I think something might be wrong in the computations that you are carrying out.


Are you sure that you are normalizing the forces with the correct coefficients ?, also it could be simply that you set the normalizing coefficients in a wrong way in OF making its results not correct.



By the way is the problem steady or unsteady, 2D or 3D ?


if the problem is unsteady you should be able to see if the forces coefficients values at different times are just multiplied by a factor with respect to the one of OF.