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Particle -laden flow using LES-DEM in OpenFoam |
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#1 |
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Hello All
I am simulating a particle-laden flow (backward facing step), which is turbulent flow case. Particles are injected from inlet after certain time and fluid and particle velocity profiles are compared with the experimental data. The case is simulated using DPMFoam. firstly, I used RANS (with dispersion model to get effect of turbulent fluctuations on particles) to resolve the fluid field, the resolved fluid fields are the used to predict the particle trajectories in the domain. The simulated fluid velocity profiles give excellent agreement with the data but particles dispersion is under-estimated, thus giving very different particle velocity profiles than that of observed in experiment. As the RANS gives the mean fields and effect turbulent fluctuations are modeled by some dispersion models, which seems to under predict the dispersion. I decided to use LES in order to get fluid fields which 80-90 % resolved, thus no need to use any dispersion model. When LES-DEM is performed, the fluid velocity profiles gives good agreement and particle velocity profile has improved than that of RANS-DEM. But still I get very less particles below the step (still particle dispersion is under-predicted. I am wondering what could be reason for that? Any Expert comments? Best Regards Atul |
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#2 |
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Filippo Maria Denaro
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First, since you are simulating a backward facing step you should check if your flow velocity is correct. There are many database for such flow to compare the statistics.
If your solution is correct, you have to consider that a filtered velocity is not exactly what appears in an experiment. The particle can have some inertia and the real velocity is a DNS-like solution. Check better the condition of the experiment. |
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#3 | ||
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Hello FMDenaro
Thanks for your answer. Quote:
Quote:
Am I doing anything wrong or missing something? What do you suggest in order to get better dispersion of particles? Best Regards Atul |
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#4 |
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Filippo Maria Denaro
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Many reasons could be possible I cannot say what happens.
From your description seems that the recirculation region is steady and isolated from the main flow. And that is wrong. You should provide the plot of the velocity profile at several stations. Could you show also the experimental data? |
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#5 | |
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Quote:
-I am also attaching plot of the particle velocity profiles at several stations, you can see that particles below y/H <1 are almost zero before reattachment point (x/H=7), they start to get dispersed after this reattachment location. Any idea, what could be the reason of it? Best Regards Atul |
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#6 | |
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Filippo Maria Denaro
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Quote:
That fact that the particles follow apparently only the mean velocity is strange. How do you distribuite the particles at the inflow? |
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#7 | |
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Quote:
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#8 | |
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Filippo Maria Denaro
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Quote:
First, I suppose that you inject only after the flow is fully developed, that is after the numerical transient is ended. Then, your particles have a mass and therefore some inertia, they do not follow the lagrangian trajectories. Maybe the diameter and the density is larger than the experimental ones? That could justify that fact that they are not so subject to the fluctuations. Of course, some bug in the code could be also a simple reason. |
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#9 | ||
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Quote:
Quote:
-I have tried almost everything in my knowledge but it seems the dispersion are under predicted in both LES-DEM and RANS-DEM (with dispersion model too). May be its the bug nut I am not sure. |
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#10 | |
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Filippo Maria Denaro
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Quote:
I suggest to do a check by performing first a simulation of a passive lagrangian tracer. If it works you can try increasing the density and diameter step-by-step |
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#11 | |
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Quote:
-I wanted to know what could be the reason of particle not dispersing properly below the step as found in the physical experiment. Best Regards Atul |
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Tags |
dispersion model, dpmfoam, les, particle-laden flow, rans |
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