[Jennifer Von]

Hi everyone,

I'm running a 3D cylinder simulation in FLUENT with a Re of 100,000. I've used a Transition SST model with a time-step size of 5e-04 and 200,000 time steps. Pressure and velocity coupled scheme is PISO. y plus <1 ，so does that mean mesh is ok? I'm trying to obtain the drag coefficient from this simulation

The results I've obtained shows an oscillatory motion, with the Cd value hitting a peak of 1.1 midway before falling back to 0.7 at the end of the 200,000 time steps.

I used k-e model/SST but the results are not good.


Can anyone tell me why has this occurred? What do I need to do for the Cd values to be stablised?

Thanks!

Regards,
Jennifer

[Leonardo.flores]

Hello Jennifer, could you post the Cd Report Plot? I am doing something similar for a 2D cylinder, by now I did for Re 10, 40, 100 and 200... and I am getting good results. I will model turbulence following this paper:

https://www.researchgate.net/publica...and_Validation

I am still novice in CFD, but looks like 200,000 time steps is too much... following the paper I showed you I think 5000 would be enough. Also, what is your convergence criteria for each time step? I am keeping it in 10e-06 for unsteady, and setting a high number of max. iterations per time step, so it doesnt stop before.

[Jennifer Von]

Originally Posted by Leonardo.flores

Hello Jennifer, could you post the Cd Report Plot? I am doing something similar for a 2D cylinder, by now I did for Re 10, 40, 100 and 200... and I am getting good results. I will model turbulence following this paper:

https://www.researchgate.net/publica...and_Validation

I am still novice in CFD, but looks like 200,000 time steps is too much... following the paper I showed you I think 5000 would be enough. Also, what is your convergence criteria for each time step? I am keeping it in 10e-06 for unsteady, and setting a high number of max. iterations per time step, so it doesnt stop before.

My convergence criteria are 1e-06 for unsteady and 40 iterations per time step. I checked the mass flow rate, and it is the order of 1e-07 which is small enough I think. And my case was initialized using another date file I calculated before, so it started from flow time=145s
https://pan.baidu.com/s/1jHNYtkq