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MPPIC cyclone tutroial scaled down

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Old   August 11, 2023, 04:51
Question MPPIC cyclone tutroial scaled down
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i am new to openfoam v2212, i was running cyclone tutorial, it ran without any problems,
i want to reduce the size by 1000 times, when i reduced the mesh to 1000 times, and decreased the particles and total mass of particles for 1000 times, the case will run and give convergence till particle is injected, but courant number blows up after 1 particle is injected,

is there anything i should do.. ?
decrease the mesh size may be ?
any ideas / suggestions ?
please explain in detail

thank you in advance
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Old   August 11, 2023, 09:28
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Hello,

Have you also scaled down the velocity? If not this is not surprising you get a higher Courant number if you didn't change the time step.

You say you decreased the particles: number of particles or size distribution?

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Old   August 11, 2023, 11:44
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i have changed time step decreased it,
i was simulating a swirl tube with 20m/s at inlet, 101325 pa at both dust and air outlet, worst condition was 18g of sand in 1m3 of air , i scaled down particles for "geometry's volume" tried to run the simulation, particle size is 125 micrometers, i am getting around 8500 particles per second for given volume of geometry

please tell me if i am doing anything wrong or missed out on anything else

thanks for reply
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Old   August 11, 2023, 12:02
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It's difficult to help with that few information. Do you have a MPPICFoam log file?

You can try monitoring your max velocity in the domain, using the fieldMinMax function object: https://doc.openfoam.com/2212/tools/...d/fieldMinMax/

See if your max velocity makes sense or if it's nonphysical.

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Old   August 11, 2023, 12:42
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buddy, i can share log file on Monday (2 days later), thanks for immediate reply, currently i am not able to give you rep power
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Old   August 14, 2023, 00:55
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https://drive.google.com/file/d/1sCD...ew?usp=sharing

hope it downloads

thanks in advance

Last edited by Desimuser1; August 14, 2023 at 00:59. Reason: link didnt work
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Old   August 14, 2023, 07:05
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Hello,

There is not much to do with your file: low residual, and it seems there is no parcel at all. So far so good.

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Old   August 14, 2023, 08:31
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but the simulation stops after 1 or 2 particle enters the system, and courant number shoots up from max 1.5 (lets say), to something like 8.54e+14, or 9.647e+41, like that,,

i dont know why, but log files wont save error messages, my graph is good but it shoots up, tht shot up part is not there.


https://drive.google.com/file/d/1u32...ew?usp=sharing

https://drive.google.com/file/d/1Hmb...ew?usp=sharing

https://drive.google.com/file/d/16IQ...ew?usp=sharing

spike that is there was for when i increased the time step 10 times

thanks for reply

Last edited by Desimuser1; August 14, 2023 at 09:33. Reason: added links to graph
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Old   August 14, 2023, 09:46
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In general, coupled Eulerian-Lagrangian models are mesh dependent, and the MP-PIC is a much more mesh-sensitive method, and making the mesh 1000 times finer will cause problems. You'd have to decrease the particle size equally. Make sure your particle size is at least 2-3 times smaller than the approx cell size (or cube root of cell volume). Furthermore, a fine mesh naturally will result in higher courant values if the velocity and the timestep remain same. At the end of the day, you'll have to find optimal conditions for the numerical setup.
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Old   August 16, 2023, 00:21
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thanks for reply utkan

i will try it out

after trying: i got scaled up geometry working, my boundary condition was wrong for velocity (i had given zero gradient at outlet), i have changed it to pressureInletOutletVelocity BC

Last edited by Desimuser1; August 21, 2023 at 06:30. Reason: tried the advice
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Old   August 21, 2023, 06:28
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i started to use original geometry, dia 16mm , velocity of 20m/s, 101325pa at both air and dust outlet, case condition is 18g of sand in 1m3 of air, (i have scaled it to my volume flow rate), and particle size is 88 micrometers, (i get around 126,000) particles passing through it in 1 second, but it is not simulating, i have attached the log file,

thank for reply in advance

https://drive.google.com/file/d/1wHU...usp=drive_link

https://drive.google.com/file/d/126_...usp=drive_link

https://drive.google.com/file/d/12Pk...usp=drive_link

https://drive.google.com/file/d/1cD4...usp=drive_link

https://drive.google.com/file/d/1XTt...usp=drive_link

https://drive.google.com/file/d/1mh6...usp=drive_link
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Old   August 21, 2023, 10:52
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It seems to me that your numerical setup is not properly built. I'd activate the adaptive time stepping. Also, I'd use the code from the OpenFOAM Foundation (.org) for the MP-PIC method.
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Old   August 23, 2023, 02:43
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FOR ADJUSTABLE TIMESTEP

i had changed control dict to adapt to adjustable time step (macCo 1), but as soon as the particles start hitting dust outlet or air outlet, courant number shoots up very high from 1 or 1.001.. like that to 10^30 something, the adjustable time step corrects by doing time step in the order of 10^-47 like that,

i am thinking boundary conditions might be the problem

for velocity
@inlet - -20 fixed value at z
@dustOut - pressure inlet outlet velocity ,value = 0 (just like base case - cyclone) (i want to try with zeroGradient)
@airOut - pressure inlet outle velocity, value = 0 (just as base case - cyclone) ( i want to try with zeroGradient)

for p
@inlet - zero gradient (i want to change this to fixed flux pressure, value 0)
@dustOut - fixed value (101325/1.2)
@airOut - fixed value (101325/1.2)

if i dont insert particles i am getting convergence at 10-6 accuracy with mesh of 1.2 million cells, (limited computing power)

FOR ORG VERSION

i had tried ofv10 from the start, the original tutorial of the v10 (Mppic - cyclone) was no running proerly, i.e. Allrun script didnt work for the original tutorial case, so i thought it would be easier to do on v2212

FOR NUMERICAL SETUP

i was asked by the client to simulate these consitions and their geometry, i cant change anything

thanks for the reply in advance

Last edited by Desimuser1; August 23, 2023 at 03:29. Reason: updating numerical setup
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Old   August 23, 2023, 03:21
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i had given escape BC to both air and dust outlet,
in the image, it tells 1 particle has escaped, but in dust and air outlet, it tells 0 particles has escaped, so where did it escape to ?

currently i thought to run the simulation till i get covergence of 10^-5 accuracy (with new BC), then i will put particles in it

thanks for reply in advance
Attached Images
File Type: png Screenshot from 2023-08-23 11-46-41.png (98.7 KB, 14 views)

Last edited by Desimuser1; August 23, 2023 at 03:38. Reason: update
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