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vetnav November 17, 2012 03:41

Question about Fluent MHD module
2 Attachment(s)
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

vetnav November 17, 2012 16:14

No one is familiar with MHD module here?? :confused:

mahyar857447013 October 17, 2013 19:57


Originally Posted by vetnav (Post 392714)
No one is familiar with MHD module here?? :confused:

hi,i think i can help u

Yanlong Li October 20, 2013 00:21

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.

tyhbd January 21, 2015 05:37

The operation sequence is very important
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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