Hi
I want to model a rotating cylinder heated by uniform heat flux with cross flow by ANSYS CFX, so I have to calculate Nusselt number on the rotating solid wall of the cylinder, but the program don't give me this option. Beside I need to draw a contour of the heatline and the program has the temperature contour only.
Thank you
Ghassan
Dear Dr. Ali Shakir Baqir
Can you tell me how can I draw the heat line contour using ANSYS CFX.
Thanks
Hi,
I did it long ago, and actually I do not know if it still works fine. Apart from correlations that you can find in literature, and considering that you have to define a reference length scale for the problem, Nu= HL/k where H is the WHTC, computed by CFX (area averaged) as H=q/(Thot-Tcold) with q as wall heat flux, Thot temp of the heated surf and Tcold temp of the cetral near wall node. All the needed parameters are available in CFX post. the tricky part is that by default Tcold is considered as the near wall node temperature, making the Nu values unreasonably high. It can be mitigated using the "expert parameters" and setting "tbulk for htc" as true in the Physical Models Parameters section (look at the Ansys CFX guides for that). In any case evaluate the results with care due to the choce of L.
If you want to plot its value:
- create a line/polyline in cfxpost;
- write an expression for Nusselt number;
- use chart option and plot Nu on the created line/polyline.
I hope you find this helpful.
Hi Ghasssam, what is the message that CFX has got to you? Maybe I can help you is I understand the error
Any expression that you want to evaluate in CFX is calculated for entire domain. Integrals can be calculate at some specific location, but simple expressions as Nu= HL/k are calculate for all regions. The temperature that you will use, is done as Paoluzzi wrote.
The lines or polylines are not able to perform calculations, only superficial or volumetric zones are able to do that. The 1D geometric entities extract the results from field variables or new variables evaluated by expressions.
- Create a expression to evaluate the Nu ( the Paoluzzi's answer)
- Create a new variable and in its definition set the expression to Nu
- Calculates its Global range ( zero division or syntax error will be warning by the code - fix that if it is the case)
- Create a plane that intersect the cylindrical wall
- Create a polyline - choose the option based on the plane and wall intersection
- Choose sample and a good number of point samples (according your mesh resolution)
Now you have the expression for Nu, a new variable for Nu and a line or a set of lines where you will extract the Nu Variable values. You can plot contours, and isosurfaces also because you have a User variable.
- In the chart create a plot and choose the location as you polyline.
- Set in X axis some coordinate reference as X, Y, Z or r if you create a expression to calculate radius and the perimeter based on it ( the procedure is the same applied for Nu. You have the option to choice the line count.
- Y-axis, choose the NU variable and generate the plot
You now can export this values to a txt, dat or csv file and plot in a better data program as tecplot, or origin. Perform the radius, angle or perimeter calculations with this exported data.
Save the state file to have this procedure available for new calculations.
Dear. Dr.
Good day. I think you should work with licence CFX program and meet our groups that works with these filed.
T
Regards
Dear Dr. Ali Shakir Baqir
Can you tell me how can I draw the heat line contour using ANSYS CFX.
Thanks
Thank you Ricardo Vicente de Paula Rezende and Paoluzzi.and Iwant if you show me how to plot Nusselt as function with time
do you understand how to draw heatline by cfx or fluent software? if you know it please share it with me. thanks alot
We have comlete course on heat transfer CFD in Fluent
Writing the expressions in CFX is explained in detail here:
https://farcfd.wordpress.com/2018/02/16/expressions-in-cfx/
Interesting question Dr Ghassan Fadhil Smaisim.
I agree with you
Ricardo Vicente de Paula Rezende.
Regards!
I would like to calculate the local Nusselt number, for the time instant equal to 3000 seconds. Any suggestion? Please see attached file
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