[Nek5000-users] Pipe flow

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

Hi,
the pressure gradient is a constant force in the axial direction (i.e. 
no radial dependence). You can then, via a simple force balance, compute 
the resulting wall shear stress, which then together with the chosen 
Reynolds number (i.e. what you set in the rea/par file) defines you the 
friction Reynolds number.

I don't have the formulas for pipe flow ready, but in channel flow it 
becomes:

ffz = -dpw/dx = tauw = 1/Re_cl*dU/dy|w

and with that

Re_tau=Re_cl * sqrt(-dpw/dx)=Re_cl * sqrt(ffz).

So you can easily set the combination of ffz and Re_cl for a target 
Re_tau. Note that you would like to have U_bulk as close to 1 as 
possible in order to accelerate convergence.

Best regards,
Philipp



On 2018-04-19 10:45, nek5000-users at lists.mcs.anl.gov wrote:
> Dear Philipp,
> 
> Glad to hear from you. Would you please tell me more about the presusre 
> gradient setting, i.e., what ffx should be in terms of different shear? 
> I didnt find any guide to set that online.
> 
> Kind regards,
> 
> Zhai
> 
> 
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>