Re: Turbulence Models
Hello Sumit,
in addition to the answer of Mathias:
(1) Exactly this is what you do in a classical way: Here a very good paper on it:
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/consistent-subgrid-scale-modelling-for-lattice-boltzmann-methods/7CB8A5DE28CFB82D4FFE21947F13F9C8
(2) This is tricky: It really depends on what kind of velocity and subsequent time scaling you apply. By using advective scaling, your velocity and time step increases linearly leading to a very high Mach number and, thus, initializes non-linear growing of instabilities. Diffusive scaling (delta x^2 -> delta t) on the other hand would limit the time step by just changing charU at constant latticeU. On scaling Mathias is the hardcore expert anyway.
(3) To resolve all scales like in freely decaying turbulence you need to resolve the “Kolmogorov length scale”. This is perfectly resolved. We actually did this in our recent work for isotropic turbulence. Regarding you have a wall-bounded flow. The flow is assumed to be resolved when you resolve the wall nearest turbulent energy structures by u+=y+. Let me know if you need any assistance.
Best,
Patrick