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Question about Fluent MHD module

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Old   November 17, 2012, 03:41
Default Question about Fluent MHD module
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Hello Fluent users,

I am a beginner in Fluent. I want to learn the MHD module of Fluent. I am using Ansys 14.0. First to familiarize with the work flow process, I went through lot of tutorials. Then, I simulated the simple Plane Poiseuille flow building the case from scratch. At the end of the simulation, as expected I could see fully developed parabolic velocity profile at the exit, which matches with the analytical solution.

After this, I wanted to simulate the Hartmann flow (MHD analog of plane Poiseuille flow). I enabled the MHD model and chose Hartmann number to be 20 (B_y= 7.64 Gauss, Please look at the attached doc Hartmann flow). After finishing the simulation, I plotted the velocity profile at the exit and could see the flattening of the velocity profile (please look at attached doc Hartmann flow2), which indicates that Lorenz force is included in the momentum equation. BUT, I saw something weird in residuals. I am pasting the few lines of the residuals

iter continuity x-velocity y-velocity uds-0 time/iter
67 2.0441e-03 2.5810e-04 1.7439e-06 0.0000e+00 0:02:18 433
68 1.9700e-03 2.5377e-04 1.6280e-06 0.0000e+00 0:01:50 432
69 1.9788e-03 2.4879e-04 1.5121e-06 0.0000e+00 0:02:54 431
70 1.8832e-03 2.4463e-04 1.3903e-06 0.0000e+00 0:02:19 430
71 1.8296e-03 2.4055e-04 1.2924e-06 0.0000e+00 0:01:51 429
72 1.8519e-03 2.3598e-04 1.1889e-06 0.0000e+00 0:02:54 428
73 1.7622e-03 2.3213e-04 1.1002e-06 0.0000e+00 0:02:19 427
74 1.6380e-03 2.2828e-04 1.0365e-06 0.0000e+00 0:01:51 426
75 1.5052e-03 2.2433e-04 9.8247e-07 0.0000e+00 0:01:29 425
76 1.4334e-03 2.2096e-04 9.0770e-07 0.0000e+00 0:02:35 424
77 1.3249e-03 2.1788e-04 8.6937e-07 0.0000e+00 0:02:04 423

What is this uds-0? is it related to the Poisson equation for electric potential? Why is this always zero? is this normal? I appreciate your help.

Thank you
Attached Files
File Type: docx Hartmannflow.docx (94.4 KB, 157 views)
File Type: docx Hartmannflow2.docx (90.7 KB, 138 views)
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Old   November 17, 2012, 16:14
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No one is familiar with MHD module here??
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Old   October 17, 2013, 20:57
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Originally Posted by vetnav View Post
No one is familiar with MHD module here??
hi,i think i can help u
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Old   October 20, 2013, 01:21
Yanlong Li
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If your simulation is 3D, there should be three uds (uds-0,uds-1,uds-2 stand for B_x,B_y,B_z), which are three equations.
The rediduals is weird, check your setting.
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Old   January 21, 2015, 05:37
Default The operation sequence is very important
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According to my experience, we should first do the regular initialization and then do the MHD initialization at the MHD panel. When we do the initialization at the MHD panel, it is also important to first click the button "initialize MHD" under "solution control" label and then click the button "Apply External Field" under the "External Field B0" label. The sequence is very important.
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Old   May 30, 2016, 10:15
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hi every body

in my simulation, I should calculated the electric field intensity and so computing aggregation rate with writing udf ,in population balance model, becouse the electric field causes agregation. can I compute the electric field intensity with mhd model? and in writing udf,I do not need to calculate the field through the writing udf?

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