multiphase simulation

jimi · November 5, 2009, 08:57

Hello everybody !

I'm pretty new to Fluent, and i have to treat a diphasic problem.
But I don't know how to treat it.

I only know how to do with only Air's inlets, but now I want to do two inlets, with one in Air, and the other in Oil (Fuel) for a combustion problem. I have to know how it will be mixed in my volume.

To make it esay, I have tried to do a simple Face (1m*1m) with two velocity inlets, and one outflow.

I saw that Fluent have a Multiphase modul, but how should I use it ?
What's more, I didn't see Oil material, just mixture Fuel-Oil-Liquid. Is it what I want ? (I'm french...)

If you can tell me what I have to change in order to do diphasic (multiphase) instead of simple Air or watter , it would be great !

thank you in advance !

mazdak · November 9, 2009, 05:13

Hi

You must use a model that is called VOF(volume of fluid) if fuel and air are mixed. If the fuel is in liquid droplet situation,the droplet are treated as a discrete phase made of spherical particles which are dispersed in the continuous phase(air).In this manner you must use lagrangian method(DPM)(discrete phase model). I mean you trace each droplet individualy.

In general, the detailed flow field is computed first, then a representatively large number of particles are injected in the field, and their trajectories determined by following individual particles until they are removed from the gas stream or leave the computational domain.

sircorp · November 9, 2009, 07:46

Well Jimi

In fluent you may struggle initially but once we keep going you will love. Multiphase systems do get complex.

I did a simple test today just for mixing. When Water and Gas are mixed Fluent has a example. You can change the inlet. Create mixture at the inlet of two separate phases and third phase can have separate entry. It works well for two gases and a liquid.

However, you need to calculate
1) viscosity of the mixture
2) Density
3) Conductivity etc before tring the three phase system.

Alternative is better: Lots of study and study and study

jimi · November 9, 2009, 14:41

hy ! thanks for your answers.
I try to learn how to use multiphase for my problem, and what to use exactly because of the wide range of option... but the user's guide is very very big and complicated !

But for me, I just want to have two boundary conditions as velocity inlets. I have created two velocity inlets but I don't know how to input different fluid in each inlet. You see ?

I need to input fuel from one, and Air from the other, and after these fluids can mixed themselves into the volume...

I tried VOF, mixture, or Eulerian, but each time i'm obliged to input the two phases in each inlet, or I don't want to have fuel inflow in the Air-inlet, and vice versa whereas Fluent just let me modify the secondary phase volume fraction...

Does anyone have the clue ?

jimi · November 12, 2009, 15:05

hello !

I think I've solved my problem thanks to the unsteady way and VOF.
I got the right effects, but do you think, for my problem, that there is a better way to solve ? eulerian perhaps ?
Remenber that it is a double inlets problem, with fuel, and air.

sircorp · November 16, 2009, 18:55

Well Jimmi

Seems you solved the problem , congratulations. Did you use UDF. Also how did you do that.

jimi · November 16, 2009, 19:28

Hy.
I've just set the fuel volumic fraction to 0 for the air inlet and to 1 for the fuel one, in the VOF module.
next I initialized it to 0 in all zones, and I started my computes.
It seems to be enough for what I wanted.

sircorp · November 16, 2009, 20:55

No worries Jimi

That is what it allows. Basically setting 0 for one fluid and 1 for another means it is not multi but a sinlge fluid.(I am new to CFD and hence discard my comment if not correct).
(I did try this approach frist)

But as as long as it work for your project, that is good enough.

Good Luck

November 5, 2009, 08:57	multiphase simulation	#1
jimi New Member Jérémy Join Date: Oct 2009 Posts: 7 Rep Power: 17	Hello everybody ! I'm pretty new to Fluent, and i have to treat a diphasic problem. But I don't know how to treat it. I only know how to do with only Air's inlets, but now I want to do two inlets, with one in Air, and the other in Oil (Fuel) for a combustion problem. I have to know how it will be mixed in my volume. To make it esay, I have tried to do a simple Face (1m*1m) with two velocity inlets, and one outflow. I saw that Fluent have a Multiphase modul, but how should I use it ? What's more, I didn't see Oil material, just mixture Fuel-Oil-Liquid. Is it what I want ? (I'm french...) If you can tell me what I have to change in order to do diphasic (multiphase) instead of simple Air or watter , it would be great ! thank you in advance !

November 9, 2009, 07:46	multiphase simulation	#3
sircorp Member Shane Join Date: Oct 2009 Posts: 52 Rep Power: 17	Well Jimi In fluent you may struggle initially but once we keep going you will love. Multiphase systems do get complex. I did a simple test today just for mixing. When Water and Gas are mixed Fluent has a example. You can change the inlet. Create mixture at the inlet of two separate phases and third phase can have separate entry. It works well for two gases and a liquid. However, you need to calculate 1) viscosity of the mixture 2) Density 3) Conductivity etc before tring the three phase system. Alternative is better: Lots of study and study and study

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November 9, 2009, 05:13		#2
mazdak Senior Member MAZI Join Date: Oct 2009 Posts: 103 Rep Power: 17	Hi You must use a model that is called VOF(volume of fluid) if fuel and air are mixed. If the fuel is in liquid droplet situation,the droplet are treated as a discrete phase made of spherical particles which are dispersed in the continuous phase(air).In this manner you must use lagrangian method(DPM)(discrete phase model). I mean you trace each droplet individualy. In general, the detailed flow field is computed first, then a representatively large number of particles are injected in the field, and their trajectories determined by following individual particles until they are removed from the gas stream or leave the computational domain.

November 9, 2009, 14:41		#4
jimi New Member Jérémy Join Date: Oct 2009 Posts: 7 Rep Power: 17	hy ! thanks for your answers. I try to learn how to use multiphase for my problem, and what to use exactly because of the wide range of option... but the user's guide is very very big and complicated ! But for me, I just want to have two boundary conditions as velocity inlets. I have created two velocity inlets but I don't know how to input different fluid in each inlet. You see ? I need to input fuel from one, and Air from the other, and after these fluids can mixed themselves into the volume... I tried VOF, mixture, or Eulerian, but each time i'm obliged to input the two phases in each inlet, or I don't want to have fuel inflow in the Air-inlet, and vice versa whereas Fluent just let me modify the secondary phase volume fraction... Does anyone have the clue ?

November 12, 2009, 15:05		#5
jimi New Member Jérémy Join Date: Oct 2009 Posts: 7 Rep Power: 17	hello ! I think I've solved my problem thanks to the unsteady way and VOF. I got the right effects, but do you think, for my problem, that there is a better way to solve ? eulerian perhaps ? Remenber that it is a double inlets problem, with fuel, and air.

November 16, 2009, 18:55		#6
sircorp Member Shane Join Date: Oct 2009 Posts: 52 Rep Power: 17	Well Jimmi Seems you solved the problem , congratulations. Did you use UDF. Also how did you do that.

November 16, 2009, 19:28		#7
jimi New Member Jérémy Join Date: Oct 2009 Posts: 7 Rep Power: 17	Hy. I've just set the fuel volumic fraction to 0 for the air inlet and to 1 for the fuel one, in the VOF module. next I initialized it to 0 in all zones, and I started my computes. It seems to be enough for what I wanted.

November 16, 2009, 20:55		#8
sircorp Member Shane Join Date: Oct 2009 Posts: 52 Rep Power: 17	No worries Jimi That is what it allows. Basically setting 0 for one fluid and 1 for another means it is not multi but a sinlge fluid.(I am new to CFD and hence discard my comment if not correct). (I did try this approach frist) But as as long as it work for your project, that is good enough. Good Luck