I am planing to observe critical Ra for onset of convection in 2D geometry with density as Boussinesq approximation, and all other properties are constant. I am using laminar model. But I am seeing convection cells formation even below 1708. I have not found any example how to simulate Rayleigh-Benard Convection in FLUENT? Could anyone suggest something?
Are you set the flat layer geometry or 2D-cube? In cubic cavity, the 2D-flow starts from Ra = 514 with constant temperature at sides and from Ra = 152 with thermal insulated sides.
I am not sure what type of fluid you are trying to simulate or the exact problem. But I think from a 2-D (axisyymetric) you would get some form of thermal convective instabilities but not the exact Rayleigh-Benard convection as described by Benard. This you can achieve with 3D simulation. But it depends on the type of liquid and the thickness. I assume you are trying to simulate a 2-phase flow so you need to have an added UDF function into your simulation if you are using Fluent. Try finding the Boiling tutorial of Fluent. It can help a little.
I am simulating 2D geometry with bottom plate hot and top plate cold with air as fluid. It is a single phase phenomena. Sides have symmetry boundary conditions (open).
make sure that you have activated the 2D axisymmetric option in FLUENT.
@Mehrdad, I actually verified all BCs. I have symmetry BC on sides and i think i do not need axisymmetric option as i have isothermal BC on bottom and top wall.
And what grid size You use? Probably, the time step is large and the simulation is unstable?
I modeled the exact problem in Fluent. You set to 2d-planner. Check you Ra and Pr number(by checking the values of material properties). you mean at Ra=1708 you want to see the convection cells. This problem is a nondimensional problem, and it depends only on Ra and Pr number and aspect ratio.
i think you should set Ra=1708 and Pr=1 and aspect ratio=1 (square domain)
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