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User energy source problem in FLuent

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Old   March 24, 2020, 04:25
Default User energy source problem in FLuent
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Ali Ashraf
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My problem is basically fluid-flow in a smooth transparent pipe. I aim at adding heat generation source term(W/m3) in each cell to simulate the absorption of solar radiation by the fluid. I use Matlab code to calculate the value of the heat generation term then I insert it to fluent (cell zone conditions>>profiles>>write>>changing the numbers then read the file again), however, the net user energy source I get from fluent(Report>>fluxes>>) is higher than the value I expected and calculated from Matlab. I have tried refining the mesh but the same problem exists. (I have noticed (from the .prof file extracted from Fluent) each cell has three points which all I give the same heat source value ). I don't know the reason for this mismatch between the values I inserted and the way Fluent interprets them??
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Old   March 24, 2020, 04:43
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The three values in the profile that you extracted from Fluent are the coordinates of the cell. Those should not be changed. You need to add fourth value representing your source.
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Old   March 24, 2020, 10:46
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Thank you Vinerm for your reply, I understand that the fourth set of points in the .prof file is where I should put my values, I mean that each element I have will produce 3 points form 3faces of it. For example: if I have only one element in the domain the .prof file will have 3 X s , 3 Y s and three Z s and of course three points at the fourth set. if I want to add a 1000W/m3 source term for this element. I replace the 3 values of the fourth set to be all 1000 and reread the file. This is what I do but don't get accurate results especially when I have a different energy source for each element.
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Old   March 24, 2020, 10:54
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Profile file is written either for faces or for cells. When it is written for faces, then each face is individual. There is no connection between the faces. So, the fourth value will be applied at the center of the face.

When profile is written for cell center, then also only three values are written and not nine. These three values correspond to the center of the cell. Here again, fourth value will correspond to the field you wish to apply and it will be applied at the center of the cell.

There is no cell type with three faces; smallest 3D topology with planar faces is tetrahedron, requiring four triangles.
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Old   March 24, 2020, 13:58
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IIRC, Fluent does not allow you to even use a profile for specifying volumetric source terms. You are somehow doing something different...
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Old   March 24, 2020, 14:27
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Profiles can be used for source terms.
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Old   March 27, 2020, 08:32
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Thank you Vinerm, the written file I get -as we might expect- should have coordinates for cell center (three values for the (x,y,z) of each cell and fourth value where you should place your source value) but what actually happens is that I have a large number of points when I interpret the coordinates I figure out that these points aren't in the center of the cell as I expected, in addition, I have more than one point per cell (by saying point I mean 3 numbers for the 3 coordinates(x,y,z) in the file). please tell me when you write a profile you get values for cell centers only (if you have 10 cells you will get 10 xs,10ys,10zs,10replacable source terms)?if so, that means I am doing something wrong
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Old   March 27, 2020, 08:45
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You cannot write a Profile from Fluent where it gives you cell centers. Profiles are written only for boundaries. So, the procedure would be to write out any value but using File > Export > Solution Data, select ASCII, cell center option. Then write out any one variable. This will write cell centers. You have to use these cell centers to create your profile.
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Old   April 12, 2020, 13:39
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Thank You again , I have been trying this method and others. Getting cell centers is good but I can't insert the file back into source terms in cell zone conditions. That's because of the fact that the number of points I am getting from cell centers is different from what ansys expects for profiles. Profiles however is the only way-to my best knowledge- to insert a user source term to certain body in my project.
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Old   April 13, 2020, 10:31
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Fluent does not care about the number of points in the profile file. All it cares about is that the number specified in the very first line mentioning the number of data points should match with the data points really provided in the file. E.g., if first line mentions 4 as its last argument and then provides number of points where either x, y, z, or source value does not have 4 points, then Fluent will give error.
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