domain definition

Zaktatir · January 14, 2010, 03:51

I am trying to simulate droplets breakup in stratified air water flow: that means i ll have:
-continuous air
-continuous water
-water droplets

which definition is the most convenient for this simulation
thxx

stumpy · January 14, 2010, 12:16

Air and Water would be Eulerian phases (like a free surface simulation) and water droplets would use Lagrangian particle tracking, with a break-up model as necessary. I've never tried to set this up, so there could be limitations in CFX.

Zaktatir · January 14, 2010, 13:21

unfortunately it doesn't work...

are ther any breakup or separation model based on the KH-theory

Zaktatir · July 6, 2010, 04:37

I modeled the problem with two continuous phases and one disperse.. but when my droplets become bigger the flow pattern changed and did not suit the normal flow pattern? what shall i do
thx Jessica

Zaktatir · July 7, 2010, 07:39

okay i think there is no interest or idea.. that s why i change my question...
is it possible to activate a phase while calculating (phase not active till something happen)

ghorrocks · July 7, 2010, 08:03

Yes, definitely. You can make a source for the volume/mass fraction which is dependent on some condition being met, maybe an elapsed time. It can trigger the source term to start generating the mass/volume fraction.

Zaktatir · July 7, 2010, 08:21

yeah i made this but i get another flow patter as expected.
I should define a positive source: that means that droplets are being separated leading a negative source for the water phase

jessica

ghorrocks · July 7, 2010, 19:03

Quote:

yeah i made this but i get another flow patter as expected.

What is a "flow patter"?

Zaktatir · July 8, 2010, 02:50

sorry flow pattern..

I made a condition: if relative velocity betwwen water/air phase exceeds a critical velocity there will be water stripping and droplet formation. At this point the droplet phase should be activated (in each cell)... I introduced source term (for the droplet phase) and the same source term but negativ for the water phase (is this correct).. The Diameter will be then calculated (capillary waves approach)

The flow pattern should be similar to that without this additionally phase but it does not work??

January 14, 2010, 03:51	domain definition	#1
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	I am trying to simulate droplets breakup in stratified air water flow: that means i ll have: -continuous air -continuous water -water droplets which definition is the most convenient for this simulation thxx

July 6, 2010, 04:37		#4
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	I modeled the problem with two continuous phases and one disperse.. but when my droplets become bigger the flow pattern changed and did not suit the normal flow pattern? what shall i do thx Jessica Last edited by Zaktatir; July 7, 2010 at 04:04. Reason: :

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January 14, 2010, 12:16		#2
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	Air and Water would be Eulerian phases (like a free surface simulation) and water droplets would use Lagrangian particle tracking, with a break-up model as necessary. I've never tried to set this up, so there could be limitations in CFX.

January 14, 2010, 13:21		#3
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	unfortunately it doesn't work... are ther any breakup or separation model based on the KH-theory

July 7, 2010, 07:39		#5
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	okay i think there is no interest or idea.. that s why i change my question... is it possible to activate a phase while calculating (phase not active till something happen)

July 7, 2010, 08:03		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Yes, definitely. You can make a source for the volume/mass fraction which is dependent on some condition being met, maybe an elapsed time. It can trigger the source term to start generating the mass/volume fraction.

July 7, 2010, 08:21		#7
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	yeah i made this but i get another flow patter as expected. I should define a positive source: that means that droplets are being separated leading a negative source for the water phase jessica

July 8, 2010, 02:50		#9
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	sorry flow pattern.. I made a condition: if relative velocity betwwen water/air phase exceeds a critical velocity there will be water stripping and droplet formation. At this point the droplet phase should be activated (in each cell)... I introduced source term (for the droplet phase) and the same source term but negativ for the water phase (is this correct).. The Diameter will be then calculated (capillary waves approach) The flow pattern should be similar to that without this additionally phase but it does not work??