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-   -   DPM question (http://www.cfd-online.com/Forums/fluent/46671-dpm-question.html)

Richardson November 26, 2007 12:02

DPM question
 
Hello experts,

I was wondering if someone could help me with a question I have concerning the DPM model. I am working on a particle fragmentation model for coal combustion. My question is: is it possible to convert a solid particle in Fluent into two particles of smaller diameter when they impact a wall during a simulation? Has anybody done this before? Of course, the model will evolve to a much more complicated criterion for fragmentation based on char burnout. I found a paper on this subject but naturally the Authors do not divulge much information. Any help will be appreciated.

Thanks

R


Allan Walsh November 26, 2007 15:02

Re: DPM question
 
In theory. We have looked into this casually but haven't gotten too far. There is a UDF for particle fragmentation and coalesence which isn't that clear to me. The issues of coarse will be creating new particles and keeping mass conservation. I'm not sure what the data structures are for particles - linked list? Array? One of these days we'll approach it - perhaps by then you will have figured it out and posted back here! Good luck.

Richardson November 26, 2007 17:10

Re: DPM question
 
Thanks for the reply!

I am reading a paper where the authors claimed to have written a subroutine in Fluent to incorporate fragmentation. They admitted the complexities involving mass conservation and how the particle density and diameter is defined in the defualt combustion model so they ended up having to rewrite the combustion model entirely to include fragmentation. What confuses me is that the authors aren't clear as to whether or not they actually tracked a particle-it "fragments"-then track the child particles-they "fragment"-and so on and so forth during the simulation. I will talk with some Fluent engineers and get back to this forum if I can resolve this issue.


rana November 27, 2007 11:43

Re: DPM question
 
Dear Allan,

Not exactly a similar topic for this question, but definitely it leads to the same place. Can you tell if the follewng expression of the tangential velocity of the impinging partcile (impnging a wall) in DPM - 3D model is correct or not ?

tang_vel = sqrt(p->state.V[0]* p->state.V[0]+ p->state.V[1]* p->state.V[1]+ p->state.V[2]* p->state.V[2]);

Please reply.

Kind regards,

Rana

Allan Walsh November 27, 2007 13:57

Re: DPM question
 
Without going back and checking, it doesn't really seem correct. My recollection was that the UDF manual described the tangential velocity quite well in an example, for particle erosion.

rana November 27, 2007 14:39

Re: DPM question
 
Dear Sir,

yes, it is not right as I am getting error. It is not there in the erosion udfs, there is ofcourse mention of tangetial restitution coeffcient in the 2nd example.

can you please give the correct expression of tangential velocity ?

thanking you.

Allan Walsh November 27, 2007 15:21

Re: DPM question
 
sorry, i'm just running off the airport. What's wrong with the expression in the tangentail restitution case? I have used something similar.

rana November 27, 2007 15:30

Re: DPM question
 
Dear Sir,

The problem with tangential restituion is that I dont have any data for tangetial resitution coeffcient. I just want to calculate only the tangential velocity of the particle when my particle hits the wall. The normal velocity calculation (given below) is ok, but not the tangential. velocity_normal_in = f_normal[0]*p->state.V[0]+ f_normal[1]*p->state.V[1]+ f_normal[2]*p->state.V[2];

Please help me as I am stuck in this udf. I am sorry to bother like this.

thanking you.

Richardson November 27, 2007 18:21

Re: DPM question
 
Look for an example in the UDF manual for the DEFINE_DPM_BC. I think this example has what you need.

Good luck

R

rana November 27, 2007 19:01

Re: DPM question
 
hi,

i searched the 2 examples, but cant make it out. can u just copy+paste the epresison oif u get it,

i am really looking for it.

thanks and regards.

rana December 4, 2007 10:44

Re: DPM question
 
Hi Allan & Richardson,

I made the expression and it works fine now. thanks a lot !!

Kind regards,

Rana


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