Hello all I am simulating flow over a sphere at Re = 881 where Drag coefficient must be almost Cd=0.5. I simulate it using both using laminar and Turbulent models(KOmegaSST). for laminar simulation, I get Cd ~0.5 but fort the Turbulent simulation, first of all it takes very long tome to converge and even after convergence, it gives Cd~0.65(Actually it has not fully converged yet, see attached figure). Now I have two questions; 1- what happens if I use turbulent model to simulate laminar flow? 2- when should I expect convergence based on the attached figure?
In case of laminar flows, a RANS-based turbulence model will provide a wrong solution since, generally, it is not built to switch-off when the flow is laminar.
You should change your formulation to take into account general laminar, transitional and turbulent regimes.
Thanks Dear Dr. Denaro for your response.
I tested kOmegaSST versus laminar flow and kOmegaSST gives unreasonable flowfield when I use airfoil like shape instead of sphere. I think only option left is to use LES and do averaging in time to see what is my actual flow is. what do you think?
Thanks,
Farzad
As you can see, the RANS solution produces an averaged field over the sphere also for laminar vortex shedding.
However, if you have a fully laminar flow, simply solve for it. If You think to have transitional conditions, Depending on you computational power, use LES or DNS.
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