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-   -   Sinusoidal velocity settings ? (https://www.cfd-online.com/Forums/cfx/26613-sinusoidal-velocity-settings.html)

 Adenlan November 3, 2008 05:54

Sinusoidal velocity settings ?

Hi everyone,

I'm trying to setup a sinusoidal current in cfx but it seems I don't use the proper way. I set the simulation on transient mode in inlet boundary I use a cartesian velocity with expression : U=0 V=0 W=W [m s^-1]*sin(pi[rad s^-1]*t) and initial conditions set to 0 . The problem is that it does not converge instead each iteration I have this message :

****** Notice ****** | A wall has been placed at portion(s) of an OUTLET boundary condition (at 76.5% of the faces, 77.1% of the area)to prevent fluid from flowing into the domain. The boundary condition name is: outlet.The fluid name is: Water. If this situation persists, consider switching to an Opening type boundary condition instead.

Please someone help me !

 Adenlan November 3, 2008 06:12

Re: Sinusoidal velocity settings ?

Don't mind, my error is too obvious

 underGroundMan November 4, 2008 07:47

Re: Sinusoidal velocity settings ?

Set your outlet to 1 atm and reference pressure to zero.

 Amod November 6, 2008 13:13

Re: Sinusoidal velocity settings ?

By definition, Inlet Boundary condition should have flow always into the domain and Outlet Boundary condition should have flow always out of the domain.

By specifying inlet velocity profile as a function of time, you are changing the magnitude and direction of flow at the inlet boundary. This is not acceptable mathematically!

You may have to use moving boundary problem such as movement of Piston in an internal combustion engine.

Hope it clears! Amod

 Rui November 7, 2008 04:49

Re: Sinusoidal velocity settings ?

Hi,

Why is it not acceptable mathematically?

What happens when one defines a negative (outwards) velocity on an Inlet Boundary in CFX?

P.S. There's nothing wrong in changing the magnitude of the flow at an Inlet Boundary, is there?

 underGroundMan November 12, 2008 07:02

Re: Sinusoidal velocity settings ?

I agree Rui. I have used time varying boundary condition many times and it works fine.

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