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-   -   Boundary conditions of laminar flow in pipe (https://www.cfd-online.com/Forums/openfoam/90863-boundary-conditions-laminar-flow-pipe.html)

 alireza.glz July 22, 2011 07:59

Boundary conditions of laminar flow in pipe

Hi dear foamers
I'm a new user of openfoam and I'm trying to run my first case.
My case involves heating process of a power-law fluid in a circular pipe.
The simulation involves the entrance region of the pipe, so the momentum boundary layer and thermal boundary layer are developing simultaneously.
the fluid enters the pipe with a flat velocity and temperature profiles and reaches fully developed conditions at the end.
But I don't know what boundary conditions should I use for pressure and velocity in pipe wall, centerline, pipe inlet and outlet.
:(
Can anybody here help me

 Linse July 25, 2011 13:29

Inlet boundary conditions

Dear Alireza,

unfortunately I cannot give you a complete answer. But what I tried for a beginning (and what seems to give reasonable results) was:
Inlet for any condition:
type fixedValue;
value uniform (.....);

For the walls I tried the same at first with a value uniform (0 0 0) for the velocity, but obviously I am not yet happy with it. I will try to find better boundary conditions there the next days.
For the outlet up to now I am using a mixture of fixedValue-type and zeroGradient-type boundary conditions. The profile does develop reasonably well. But still, I am not completely happy with the wall conditions and my results with a simple Bernoulli equation are far from what I get in the simulations (yet).

Hope that helps?

Maybe someone can tell us the thread where the different wall-BCs are well-explained, especially concerning setting parameters and so on? ;-)

 romant July 26, 2011 08:56

wall boundary conditions

Hej,

for the wall boundary for pressure you should set it to
buoyanytPressure , the velocity should have 0 at the wall given by the fixedValue boundary condition.

At the outlet, your velocity can be set to pressureInletOutletVelocity , which
makes the velocity completely dependent on the pressure at that point. The pressure should thenbe set to fixedValue.

I assume that you are dealing with incompressible flow. This means that you can set your pressure fixed value to 0. In case of compressible flow, you need to set it to the actual pressure, otherwise you might divide by 0.

Depending on what kind of problem you deal with for your heat (constant wall temperature or constant heat flux) you might want to consider fixedValue boundary condition at all walls and the inlet, and zeroGradient boundary at the outlet.

In case you need more boundary conditions, especially for the turbulence properties. Try taking a look into the folders of the respective solvers that you are using.

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