TFM 2D fluizied bed, vibration and microjet effect question

[kejuan]

Hello, I am new MFIX user who switched from Ansys Fluent.

I am currently trying to give vibration and microjet on a fluidized bed.

My questions are,

1. How can I give downward microjet(Diameter is 500 micrometer). The location is (x,y)=(xmax/2, 0.1 meter).
   I was trying to use point-source with mass flow rate and V-velocity. Is it correct approach?

2. When I was using fluent, I used attached txt file to give a sinusoidal vibration_udf_fluent.c.txt (1.4 KB) gravity in the momentum source term. How can I give sinusodial gravity effect using UDF in MFIX?

3. I think I need to use turbulence model since the microjet velocity is 200 m/s. Which turbulence model do you recommend? k-e or L-scale?

Thanks

Keju AnTFM.mfx (13.2 KB)

[jmusser]

1. If the jet is smaller than your CFD mesh, then you will have to use a point source to introduce the effect.
2. The easiest approach is to use usr1.f to modify GRAVITY_X, GRAVITY_Y, and GRAVITY_Z.
3. That is a modeling question, based on the needs of you application.

[kejuan]

Thank you Jmusser

I have one more question.

After modifying the usr1.f, how can I compile in the Mfix?

Thanks

KJ

[onlyjus]

If you are using the GUI, follow the docs: 5.1. Building Custom Interactive Solver — MFiX 19.2.0 documentation. Make sure your usr1.f file is in the project directory.

[gq0502]

Hi Weber,

I am also interested in this topic to change the gravity with time. However, although the attached usr1.f can be built successfully. It can not work at all. In this case, I set a constant value of 0 for gravity_y, but I have still seen particles settling down.

Could you please help me check the usr1.f? Thank you very much for your help.

usr1.f (2.4 KB)

[gq0502]

I should quote the following topic here.

Vibration UDF for TFM model

I am trying to give a sinusoidal vibrational effect on gas phase and solid phase in a fluidized bed(2D TFM). There will be a displacement due to vibration, displacement, d = A * sin(2 * pi * f * time) A: amplitude f: frequency and the second derivative of vibrational displacement will be vibrational acceleration. vibrational acceleration, a = 4 * pi^2 * f^2 * A * sin(2 * pi * f * time) Using this vibrational acceleration, I want to modify the gravity term in the momentum equation for both…

[jeff.dietiker]

Please make sure you have enabled UDFs. In the GUI, go to the Model Setup pane, and check the box “Enable user-defined subroutines” in the Advanced settings.

[gq0502]

Hi Jeff, Thanks for your reply. I am sure that I have enabled UDFs. Attached are the example I run for the udf, which is based on the tutorial case fluid_bed_dem_2d. As you can see, even I have make the gravity_y=0, many particles still settle down. Looking forward to hearing from you. dem2dcase.zip (14.2 KB)

[jeff.dietiker]

For DEM, you also need to change GRAV vector. Please take a look at

mfix/legacy_tutorials/DEM_Wall_HT

To access GRAV: USE discretelement, only : grav

To overwrite gravity:

      ! Rotate gravity vector for rotating drum
      ANGLE = time * RPM*2.0D0*Pi/60.0D0 !convert RPM to rad/s
      GRAVITY_X = sin(ANGLE)*GRAVITY
      GRAVITY_Y = -cos(ANGLE)*GRAVITY
      GRAV(1) = GRAVITY_X
      GRAV(2) = GRAVITY_Y

This would make more sense to do it in usr1_des.f rather than usr1.f

[gq0502]

HI Jeff, Thanks very much for your update. It now works successfully.