[Nek5000-users] Convection velocity and outlet BC

[nek5000-users at lists.mcs.anl.gov]

Hi,
for the convective conditions, you need a convection velocity, and there 
are different ways to do that, e.g. averaging over a plane, time 
relaxation, or taking the mean velocity (e.g. from statistics). The 
important point is that you need to make sure that the global mass flux 
is correct.

The Dong condition does not need a convection velocity, as the two 
parameters can be combined into a single parameter.

I will get back to you with our implementation of the convective 
condition, sorry that I haven't done it yet as I was travelling.

Philipp

On 2017-09-17 18:59, nek5000-users at lists.mcs.anl.gov wrote:
> Dear Neks,
> 
> for different convective boundary conditions there is a parameter I need 
> to calculate: the convection velocity, which can be aproximated as 
> the mean streamwise velocity averaged at the exit plane.
> 
> Is there a quick way to calculate Uc for each time step?
> 
> Now I'm using Dong (2014) BC, but it also needs a convection velocity, 
> and I'm using an aproximate number, but I'd like to calculate the right one.
> 
> On the other hand, the BC I'd like to try now is:
> 
> (du_i/dt)+Uc*(du_i/dy)=0
> (dT/dt)+Uc*(dT/dy)=0
> 
> where the stramwise direction is y, since it is a free convection flow, 
> and Uc is the convection velocity.
> And, any idea or help to implement those BC?
> 
> Thank you very much,
> 
> Juan Pablo.
> 
> 
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