I am new to OpenLB and I would like to ask a couple of questions. They mainly focus on the example Cavity2D. First, What is the Smagorinsky effect added to the code and how can I remove it? Second of all, if he initialized a constant Rayleigh Number, why at the end of the code he specifies different Rayleigh Number?
The laminar/cavity2d case doesn’t use Smagorinsky LES. You could add it by changing the bulk dynamics type and setting the collision::LES::Smagorinsky parameter (see e.g. examples/turbulence for reference).
The example is parameterized for Re=1000 by default and compares to matching literature values. I assume you are confused by the definition of vel_ghia_RE100 in 195: This is only so you can quickly switch to the Re=100 case reference values.
One common way of extracting and plotting data is via post processing the VTK output in e.g. ParaView.
Of course it is also possible to extract this data directly inside the OpenLB application. E.g. you can extract the line data using BlockReduction2D1D applied to the SuperLatticePhysTemperature2D functor. On top of this you will then be able to compute the Theta values using either functor arithmetic or plain C++.