[cfd@kgp]

I was trying to capture the critical Rayleigh number using Openfoam buoyantBoussinesqPimpleFoam?


However, I am unsuccessful to get the onset close to Ra_c= 1708; as one has to perturb the initial field with the correct scale.



Openfoam gives the onset some were inbetween Ra = 3000 to 8000 when I dont apply any disturbances in my initial field. Also after setting fluctuations (described below) in the initial temperature field I am not getting correct Rayleigh numbers.



I am starting with the linear conduction temperature profile and superimposing a sinosidal function as a disturbance as ----> 0.1*sin(pi*x)*sin(2*pi*y) .Here, (0.1) is the amplitude of the perturbation where 0.1 is dimensionless value (i.e., 10 % of T_h -T_c)



I have tried 2d simulations for a wide aspect ratio case (5:1) with periodic boundary conditions in x-axis, with central differencing scemes for both convective and diffussive terms


Experts please share your experience/suggesstion regarding this?



Waiting for earliest positive response from anyone.


Thanks in advance