[venkatnv]

I am trying to validate the natural convection in annular flow between a hot inner circular cylinder and a cold outer square cylinder. Please let me know which solver is to be used for this problem and also how to implement the calculation of averaged Nusselt number in the solver.

[jherb]

Have a look at the buoyantSimpleFoam (or ...Pimple... for transient cases). Also if the density is not changing much you might want to use buoyantBoussinesqSimpleFoam.

(Have a look at their corresponding tutorials. Be careful with the definition of pressure with differs between the Boussinesq and non-Boussinesqsolvers solvers)

[venkatnv]

I tried both buoyantSimpleFoam and buoyantBoussinesqSimpleFoam. I'm trying to validate the case for different Rayleigh's number (10^4 , 10^6). I find that only in the latter solver there is an option to provide the values of the parameters involved in Rayleigh Number( i.e, Beta, Prandtl Number, nu, etc., in the transportPropertes file). So I solved using the latter solver but my results are not matching with the ones in the reference paper. Please let me know where I might be going wrong.

[jherb]

For buoyantSimpleFoam you can specify polynomial relations in thermophysicalProperties for these quantities.
http://www.openfoam.org/version2.2.0/thermophysical.php