CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   Straight through cyclone with particles (http://www.cfd-online.com/Forums/cfx/102078-straight-through-cyclone-particles.html)

rogerhoffmann May 21, 2012 14:59

Straight through cyclone with particles
 
Hi,

I am running some cases of a straight through cyclone, with particles. I am running it steady state, air ideal gas, k-epsilon, with Uniform in Diameter by Mass distribution (see below).

It all seemed to work fine for a series of calculations, but when I was changing some variables like, temperature (increased some degrees), reduced density of the particle material, then I began to obtain results with about 30% - 50% of the particles EXCEEDED INTEGRATION LIMIT, or DISTANCE or TIME. I tried many times to increase this limits, but all I had was huge computational time, and the results did not improve much.

My questions:
1 - Do this particles that are being terminated affect the results, or they can be just ignored?
2 - I understand that this particles are being trapped in some region of the flow. How to discover where is this happening? Could this be a mesh issue?
3 - Is it possible to know which particles are being trapped, where they originate, or their diameter?
4 - I used the Injection at Face Centres at first, but when I wanted to increase the number of particles using uniform injection (to improve the results), I also had lot of particles being terminated. Why? It seems that only using Injection at Face Centres and certain conditions I can run without particles being terminated.

Any tips, suggestions, could help.
Thank you,
Roger


FLUID: Particulas
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = Zero Slip Velocity
END
PARTICLE DIAMETER DISTRIBUTION:
Maximum Diameter = 1 [mm]
Minimum Diameter = 0.54 [micron]
Option = Uniform in Diameter by Mass
END
PARTICLE MASS FLOW RATE:
Mass Flow Rate = 6.94e-4 [kg s^-1]
END
PARTICLE POSITION:
Option = Injection at Face Centres
END
END

ghorrocks May 21, 2012 18:42

I suspect this means that as you changed the conditions then you entered a regime where the particles just go round and round and never exit the domain. This means the particle tracks get very long, computational load goes up and it terminates the tracks at the limits you define (and gives the warning message).

Your questions:
1) If the particles never leave then they might build up into a bed or something. You need to consider whether this is possible.
2) Look at the particle tracks. That should show what they are doing.
3) Yes, all this is available in the post processor.
4) Again, look for why they are terminated. Generally it is because they end up in a vortex and never leave.


All times are GMT -4. The time now is 01:22.