Rotor stator problem: Discontinuity across the interface

Bubka · November 10, 2009, 23:42

Hi!

I'm simulating a mixing vessel with impeller, baffles, etc. I've simulated it using frozen rotor as well as transient rotor stator. The flow field itself looks good (if I look at velocity in stationary frame).

But I am also solving a scalar equation (I have an inlet where a tracer comes into the vessel and I am looking at how the tracer mixes with the rest of the fluid). If I look at contour plots of this tracer, I see a discontinuity across the interface. This is presumably because of the different frames of reference.

How can I account for this discontinuity in CFX-Post? CFX-Post has "Velocity" and "Velocity in stationary frame". Does it have a similar feature for additional scalar equations?

Thanks!

ghorrocks · November 11, 2009, 06:07

If you use frame averaging then you will get discontinuities across the interface. But you are using TRS and frozen rotor and they do not do the stage averaging. The tracer concentration should not be affected by the frame of reference you should be able to view it directly and it should be continuous. Are you sure your simulation is fully converged and the mesh is adequate?

Bubka · November 11, 2009, 08:57

Hi Glenn!

Thanks for your reply. Yes, the mesh and convergence are ok. Not perfect, as the geometry is pretty complicated.

I think I'll do a test with a simple geometry and see if the same problems come up.

Thanks again.

November 10, 2009, 23:42	Rotor stator problem: Discontinuity across the interface	#1
Bubka New Member Join Date: Nov 2009 Posts: 2 Rep Power: 0	Hi! I'm simulating a mixing vessel with impeller, baffles, etc. I've simulated it using frozen rotor as well as transient rotor stator. The flow field itself looks good (if I look at velocity in stationary frame). But I am also solving a scalar equation (I have an inlet where a tracer comes into the vessel and I am looking at how the tracer mixes with the rest of the fluid). If I look at contour plots of this tracer, I see a discontinuity across the interface. This is presumably because of the different frames of reference. How can I account for this discontinuity in CFX-Post? CFX-Post has "Velocity" and "Velocity in stationary frame". Does it have a similar feature for additional scalar equations? Thanks!

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November 11, 2009, 06:07		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	If you use frame averaging then you will get discontinuities across the interface. But you are using TRS and frozen rotor and they do not do the stage averaging. The tracer concentration should not be affected by the frame of reference you should be able to view it directly and it should be continuous. Are you sure your simulation is fully converged and the mesh is adequate?

November 11, 2009, 08:57		#3
Bubka New Member Join Date: Nov 2009 Posts: 2 Rep Power: 0	Hi Glenn! Thanks for your reply. Yes, the mesh and convergence are ok. Not perfect, as the geometry is pretty complicated. I think I'll do a test with a simple geometry and see if the same problems come up. Thanks again.