[mps]

hi, does anybody know the difference between trapped and escaped particle fate in dpm in Fluent in terms of equations or B.C.? Fluent help says the particle tracking is terminated for both of them, but when I change the dpm condition in an outlet from escaped to trapped, the results for concentration distribution differs at the outlet. Is there any udf macros for escaped fate to be applied anywhere else in the domain?probably with DEFINE_DPM_SCALAR_UPDATE function?
Thanks

[edu_aero]

Originally Posted by mps

hi, does anybody know the difference between trapped and escaped particle fate in dpm in Fluent in terms of equations or B.C.? Fluent help says the particle tracking is terminated for both of them, but when I change the dpm condition in an outlet from escaped to trapped, the results for concentration distribution differs at the outlet. Is there any udf macros for escaped fate to be applied anywhere else in the domain?probably with DEFINE_DPM_SCALAR_UPDATE function?
Thanks

I was facing that question like one week ago.
When the B.C at the outlet is trapped, the velocity in that point is zero. Nevertheless, with the condition escape it does not happen.

I would like to tell you about some problem that I had and I am continuing solving. With the condition trapped, the difference between mass flow ratio at the outlet, with injection plus inlet is right always that the temperature of the outlet is less than the vaporization temperature of the droplets. This is because Fluent only calculate the mass flow ratio of vapor and not liquid.

[mps]

thank u for ur reply
I am curious about sthelse. when I put small value for Max. number of steps, obviously particles reach only the half way of the pipe, while I monitor the DPM source term to reach convergence. then I check the results, which seem ok. but if I let the iteration goes on for a while, the velocity and temperature and heat transfer will be distorted, completely unreasonable results, specially at the middle of the pipe where particles were stopped going further (incomplete fate due to small value for Max. number of steps). I know I have to put proper amount of Max. step, but why Fluent ruins the results after long iteration?

[edu_aero]

Originally Posted by mps

thank u for ur reply
I am curious about sthelse. when I put small value for Max. number of steps, obviously particles reach only the half way of the pipe, while I monitor the DPM source term to reach convergence. then I check the results, which seem ok. but if I let the iteration goes on for a while, the velocity and temperature and heat transfer will be distorted, completely unreasonable results, specially at the middle of the pipe where particles were stopped going further (incomplete fate due to small value for Max. number of steps). I know I have to put proper amount of Max. step, but why Fluent ruins the results after long iteration?

I am not sure about it.

But were me to guess, I would say that it is because you have a huge inestability were particles are forgotten.
I would bet that u are taking into account the influence of the particles in the Fluid. Because suddenly taking all the particles out of the simulation more or less at the same possition will create inestability and in my opinion it is the cause of the divergence of the solution.

I don't know if it can be helpful for u =)

[mps]

thanks. the two-way coupling is active as you said. no divergence is observed in residuals. but this leaving the calculation somewhere in the domain, probably can be the root of instability in flow results after long iteration. but Im not sure in any case. If you may have as look in Fluent tutorial for DPM, you will see that it switches off the flow residuals and only considers the convergence of DPM source term as the main criteria. now Im not sure if I should do the same and the results would be acceptable?

[edu_aero]

Originally Posted by mps

thanks. the two-way coupling is active as you said. no divergence is observed in residuals. but this leaving the calculation somewhere in the domain, probably can be the root of instability in flow results after long iteration. but Im not sure in any case. If you may have as look in Fluent tutorial for DPM, you will see that it switches off the flow residuals and only considers the convergence of DPM source term as the main criteria. now Im not sure if I should do the same and the results would be acceptable?

By divergence I meant the oscilation from the result data. But I am totally agree, it is not the best word for describing the phenomenon.
I see what you mean about the Fluent tutorial. I don't know, convergence criteria is really important and I don't like just that it seems like it is convergenced.

For that, nowadays I am trying to create a macro in order to garantee convergence by mass flux. But the problem that I am facing it is that Fluent only tells you the mass flow of gas. So that, I am creating a macro that loops through all the particles. Nevertheless, I don't know how to do it

Someone people, take into account the shape of the mass flow of gas at the exit as a convergence critaria. I mean, they suppose that it is converged when the plot is horizontal and without oscilation.