Learning Forum

[sripadarajak]

It is said that when Reynold's number is much lesser than 1 then convective terms can be removed/neglected. Simulations involving capillary flow where Re << 1, is computation is done with convective terms being removed or neglected?

[DrAmine]

Fluent is general purpose CFD Code: we are solving all parts and we are not neglecting anything based on Reynolds Number. Convective terms are always solved for and discretized. If you want to avoid that: use UDS and UDF's.

[sripadarajak]

- Thank you for your quick reply. Typically, when we linearize the PDE's second order terms are neglected. So, when you say convective terms are not neglected, then computation is done without linearizing the basic PDEs (N-S equations) ?

[DrAmine]

I am not saying that: we are linearizing the PDE's and we end up with general formula a_p*phi_p= Sum of a_neighbour*phi_neigbour + Source. Please consult the Fluent Theory Guide and any Text Book on Numerical Methods.

[aitor.amatriain]

the topic of linearizing PDEs is very broad. You can linearize many things: the original PDE, a perturbated PDE, the original PDE is weak form, the discretized PDE...
Convective terms can be neglected when Re<<1, but I see no advantage of doing that; indeed, in a flow where viscous terms are dominant one does not expect numerical problems. In the opposite case (Re>>1) , the story is totally different.