yPlus value in internal flow (natural convection in cavity)
 

I am trying to validate the turbulent case of following paper
goo.gl/xuAOwy

I am using buoyantBoussinesqPimpleFoam solver for this. Also I am using k-omega turbulence model. There are multiple points that I don't understand

1. What value of turbulent prandtl number should I use for my case(I guess unity is a good choice)?
2. Since I am using wall function so value of yPlus should lie around 30-40 but since it is a case of internal flow I don't know how to calculate grid size (since I don't know velocity near wall) . How to tackle this problem?
3. Also how to calculate deltaT value ?

Since I am new to OpenFOAM so please be elaborate even if you find my questions silly :)