When the buoyancy effect is significant in supercritical fluids passing in the tube, some eddies can form in any location of tube, especially at the vicinity of supercritical temperature. So, what is the numerical method to solve like the compressible problem? As my experience and literature, there is no way to calculate this type of problem by using RANS models, so I have just started using LES models. Although it was used a very low time step size (about E-5) and tried all of the subgrid models, I couldn't solve this problem. I would like to be grateful if you could share your recommendations. Thanks
First of all, RANS and LES are different FORMULATIONS not different turbulence models. Those two formulations compute very different variables!
If you want to perform an LES you need to know that you resolved for a 3D and unsteady filtered variable. You need to start from some initial condition, run for a long time the solver until the fields are physically well correlated and then you have to sample the 3D unsteady fields in time to perform a statistical analysis in post-processing.
Second, for compressible flow the SGS models are less theoretically developed. There are many open problems. Have a look here https://www.springer.com/gp/book/9789048128181
Third, provide the details of what you have done, what is your setting and what is the problem you think appears.
Are you looking at density variation (compressible) and phase change at super critical temperature ?
Gravitational effects in horizontal ducts are observed at very low velocities such as free-forced convection situations .
i would advise dense phase model in cfd to assess such situations.
please elaborate the problem so that we can discuss in detail.
i would suggest to look into physics so that we can choose appropriate model for analysis
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