[alireza.glz]

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
Thanks in advance

[Linse]

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? ;-)

Thanks in advance already!

[romant]

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.

[Raza Javed]

Originally Posted by romant

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.

Hello Roman Thiele,


I have somehow similar problem. I try to explain my problem as much clear as I can.


I have a fluid region and outside this fluid region, there are some hot plates. Now, I need to define some velocity at the inlet and at certain temperature (say 300K), and when the fluid reaches at the outlet the temperature of the fluid would be changed due to the hot plates outside the pipe.


At the inlet, I have a particular flow rate in the requirement.



Now, I need to calculate the temperature rise of fluid between inlet and outlet i.e, how much temperature change occur due to these hot plates outside the pipe?


But I don't know which boundary condition to choose for Velocity, Temperature and Pressure at Inlet, Outlet and wall of the pipe?


How can I use the flow rate to define velocity at the inlet?

I hope I was clear in explaining in my problem. But if you need more explanation I would be happy to provide.


I shall be very thankful, If you can help me out in this.


Thank you.

[The Mad Scientist]

Hello Javed,

I was able to understand only a little about your problem. Are you using Conjugate heat transfer model or those heat plates serves as the BC ? if you could provide a schematic of your problem I might be able to help you.