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Saima April 25, 2009 15:42

How can define interface between solid and Fluid?

I have a problem in which a heater is on leading edge of an airfoil and this airfoil is placed in Icing wind tunnel. Air is inside the tunnel at -5C. And water spray by using atomizer is also there.

I have to figure out how many water droplet impact on edge.

Could you tell me which model should i use? :confused:

Currently i am using (Eulerian+Discrete phase model).
I don't have any clue please guide me.

Secondly, how can i define interface between Heater and Fluid(Airfoil wall)?

It is very urgent.

Many Many thanks in advance.

Ralf Schmidt April 29, 2009 13:03


you have a solid heater? Than, the interface between heater and fluid is a wall. You have to define it in the mesh generating software. You might also define some existing faces as walls in fluent.

When doing so, I would suggest to allocate for each face one separate wall BC - that makes it more easy to difference the different areas when analysing your results.

For the first question: I don't know - not a specialist in multiphase flows...:)

Best wishes!

Hossam May 1, 2009 11:13

The Discrete Phase Model (DPM) alone should be enough. it is the only model in Fluent that tracks droplets. the eulerian or any other multiphase model will not track the droplet.

Saima May 1, 2009 21:26

Thank you so much for you replies. It really help me alot.


sourplum May 2, 2009 00:31


Originally Posted by Hossam (Post 214875)
The Discrete Phase Model (DPM) alone should be enough. it is the only model in Fluent that tracks droplets. the eulerian or any other multiphase model will not track the droplet.

Dear Friend,

Currently I'm using mixture model (water + air) for my project which dealing with droplets with the diameter of 0.1mm. Basically, my project is on studying the efficiency of mist eliminator system.

I'm still not satisfy with my current result as it read zero mass flow rate for water while it got some value for mass flow rate of the mixture. So, I'm looking for another scheme of multiphase model and i really need your help with DPM.

My question regarding DPM are
  1. Can we determine the size of the droplets in DPM?
  2. I also need to specify the mist loading or volume of mist over a volume of air (e.g. 0.2m3/m3) . Can we specify this value for the inlet BC in DPM?
Thanks and best regards,

Saima May 2, 2009 12:41

I want to know ,

1. Is there any technique to calculate the collection efficiency of droplets?

2. How can i define contact angle in DPM (Discrete Phase Molde).

I am eagerly waitng for reply.

Thank you and Regards,

sourplum May 2, 2009 13:01

Dear Saima,

For ur first question, what i did to calculate the collection efficiency of droplets is by dividing the droplet collected (e.g. Min - Mout) over the mass flow in (Min) and multiply by 100%.

efficiency = (Min - Mout)/ Min *100%

I can't answer ur second question as I'm not a DPM expert yet.

Best regards,

Saima May 4, 2009 00:01

Thanks 4 ur reply.

Actually i have an Airfoil and Heater is place on ledaing edge of Airfoil.

I have to calculate impingement/collection efficiency on the leading edge.

That means how much droplet Impinge on Leading edge.

kindly tell me how it's possible in Fluent?:confused:

Thanks alot...:)


Saima May 4, 2009 00:04

I have one more question related to the same problem.

1. How can i see the Droplet on leading edge???
I mean flow patteren of droplet. Becoz it is two phase how can i distinguish is it air or water droplet?

I am eagrerly waiting for your reply.

Thank you

sourplum May 4, 2009 01:55

I don't think it is possible to see how much droplets have impinge the leading edge. However, u can see the water on the leading edge by displaying the density contour. U can distinguished the two different phase as the density of both phases will be different.

Other idea that come to my mind is by adding inlet and outlet before and after ur airfoil. u can assume the quantity of the droplets that impinge on the leading edge as the nett mass flow of inlet and outlet.

Hope these will help.


prasad.ichal May 5, 2009 06:09


Is the heater is a line or a curved surface on the leading edge of the airfoil? I assume the later is true. I guess you already have exploited DPM sampling by creating surfaces and allowing particles to cross them and collecting data for those particles.

I am trying to figure out whether it's possible to deduce the fate of the particle when it impinges upon a particular face (heater in this case). Evaporation is possible depending upon the temperature and heat transferred actually to the droplets impinged/approached the heater. But I am not too sure whether Fluent tells us how many of the escaped or evaporated droplets have impinged on the surface under consideration.

I know that I am not able to arrive at exact solution in one go. :p But in the hindsight I have one suggestion to offer, which is to run the case in unsteady state mode. Using particle sampling you may be in position to judge collection efficiency. This also will help you to actually visualize the flow pattern of the droplets live and arrive at the desired parameters.

Best wishes.

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