[buj]

I'm using Fluent to model temperatures in biological tissue using Penne's bioheat equation, with UDFs for tissue metabolism, tissue perfusion, and absorption from radiation in the tissue.


I've set up a test system for now to make sure the UDFs are working properly. The model is solving and temperature profiles in the results viewer are what I'd expect to see.



My problem is that I get different values for the maximum temperature using the results viewer if I use an expression to find the max temperature in the domain vs. defining a point at the max temperature.



In my example model, the domain of interest is "tissue".

• the expression "maxVal(Temperature)@tissue" returns 38.157 °C.
• inserting a point with the options below returns 37.841 °C.
  • Domains: "All Domains"
  • Method: "Variable Maximum"
  • Location: "tissue"
  • Variable: "Temperature"

Has anyone had this kind of problem before, or might they have an idea why this is happening?

[buj]

I've contacted ANSYS support and got a solution. Posting it here in case anyone else runs into this issue.


"The reason why you are getting different values for both cases is:

• The max value of a domain (eg: maxVal(Temperature)@tissue ) gives a cell centred value (which is how Fluent operates).
• The max value you get from a point corresponds to the temperature value of the nearest node (which is how CFX and CFD-Post operate).

The cell centred value (max value of the domain) must be used to obtain a more accurate value, as this bases the value on the centroid of the cell, giving a more reasonable prediction.


In general, the usage of maxVal (either for a point or the entire domain) must be done with care, as they can be prone to spurious values depending on mesh quality."