Hello every one.

I am simulating a cyclone seperator and I have easily got convergence using K-E, K-E RNG both first and second order discritization. Using the RSM model i can only get convergence for first order but cant seem to get convergence for second order. I am using 517000 tetrahedral cells in the mesh. Can some one help me on this please Thank you in Advance.

Sal

Restart the RSM solution from a converged two equation solution. Adjust your under relaxation factors.

Should i start it from the first order discretization. Steady, unsteady, boundary conditions bottom outlet as wall or pressure outlet and if unsteady what would u recomend the time step to be and should I use transient controls and which one? I appreciate this.

Sal

I would recommend that u start using steady state first to build up pressure to create a swirling flow. Once the residual gets stable change to unsteady state because the vortex will move in quasi periodic movement. You can adjust the time step to get better convergence or u can adjust your relaxation factor.

For the bottom wall what do you recomend me to use as a boundary condition. At the moment it is defined as a wall. Do i need to change? if yes what to and would I have to enter any other parameters. Thank you for the help in advance.

Sal

While running the boundary conditions i get no reverse flow. Does any one know how to correct this. Thank You. Sal

Hi,

For cyclone, there are some basic steps in CFD.

1. For meshing - Always use structured mesh (hexahedral elements) with aspect ratio within the range 5 to 10. 2. solver setup - RSM turbulence model is recommended. First solve with default setup with RSM. Once converged, then go to higer order discretization with increased converge monitor 1e-6. 3. Choose time setup size as analysis should converge in every time step.

Note: first order converged solution always gives some appropriate values. dont worry about. Cyclone phenomena is purely unsteady. So unsteady with higher order discretization, you can more accurate solution.