Dear all :
I'm trying to solve the following problem using COMSOL Multyphysics.
I have an enclosed geometry (please see the attached images) with a top flat surface (the celing) and an undulated shaped bottom surface (the floor). And I have Air as a medium enclosed inside this cavity.
So, I want to solve for fluid Velocities (u and v) distribution of the air inside the cavity, and for its Temperature distribution too.
So, I already included the physics modules: Laminar Flow (for single-Phase Fluid Flow) and Heat Transfer in Fluids.
However, I'm sure I'm doing something wrong witht he Boundary Conditions (it can be observen from the first attached image, that I don't get any velocities distribution for the air mass).
The BC I am trying to stablish are the following :
i. Isothermal Walls in all the interior walls of the cavity.
ii. No-slip Boundary Condition (u=v=0) in all the walls (on the inside) of the cavity.
iii. A constant Temperature at the upper flat surface
iv. A constant Temperature at the bottom (wavy floor) surface of the cavity.
Where the problem could be at ? The Velocity Stream Lines and Temperatures Contours should show a kind of oval spiral pattern at the top of each of the 'valleys' of the wavy bottom surface. But as depicted in the image, I don't get any valocities distribution.
I will really appreciate if someone can give some help.
Thank you all !
Best Regards !
Hi Franklin Uriel Parás Hernández,
so fas so good, but what are your initial conditions and according to them what is the physicall effect making the air move in your domain? I suppose, you want to see some movement caused by the density differences,...buoyancy? If that is the case, you need to check if you solve an incompressible problem. In such a case, the density will remain constant and the air will not move. A simple way to make the task less computationally intense and at the same time to consider the buoyancy would be to use the Boussinesq approximation. This will account for the buoyancy force resulting by the density differences, but still consider a cosntant density and hence an incompressible fluid. There is a tutorial in COMSOL for this, check it :).
Best of luck!
Antoni
Franklin Uriel Parás Hernández
I agree with Antoni Artinov . As hint you need to add two other things to your fluid flow physics:
1- Add "Volume force" to consider the buoyancy using the Boussinesq approximation.
2- Add "a point pressure constrain" to help comsol to solve the problem.
Finally use Air density change and model it as compressible flow is more accurate.
Dear Amir Reza Ansari Dezfoli :
Thank you for your reply
1. I already added this "Volume Force" domain constrain to the model in the Laminar Flow physics. This is the expression I'm using to represent this Force:
Fy = rho0*g_const*(T-T_0)/T_0
2. I think this is what I'am missing in my model, but I don't know how to add this constraint, Can you help me ?
I'm sending you a printscreen of the geometry with all the points highlighted.
¿What point (or points) do I have to select? and What value of Pressure do I have to enter?
I will really appreciate your help with this, as as you said, this might be what I need to run the simulation.
I'm using an expression to state the Density as a variable in function of the reference Pressure and Temperasture. (I'm sending you a Printscreen too)
Finally, I already select the Compressible flow (Ma
Franklin Uriel Parás Hernández
First of all; you can send me your comsol file if your version is below 5.3 (perfectly 5.2). I can check and correct your model.
About "pressure point constrain", its not important which point you select because this is just a reference for comsol for numerical operation. Then select any (just one) point in your fluid domain. The value can be equal to initial pressure (1 atm).
Remember :
1- In "Fluid Properties 1" , Temperature from "Heat transfer model" is selected.
2- In, "volume Force 1" you select your fluid flow domain.
Dear Amir Reza Ansari Dezfoli :
Thank you very much for your help, I already adjusted the "Pressure Point Constraint" and the reference value for the Pressure, and nothing.
I'll send you my model on Inbox, I'm using the Comsol's 5.1. ver
Thank you again , hopefully I was close to the answer, with the model, I'm sure you will be able to tell me what my problem was.
Regards !
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