Using CFD-Post to calculate the Local Nusselt number on the surface of a horizontal cylinder

- December 10, 2019 at 7:44 pm
  
  DavidB7
  Subscriber
  
  Hello,
  
  I am currently solving the case of forced convection across a heated horizontal cylinder (with constant surface temperature conditions). I know the equation to calculate the local Nu= - dT/dr (which is the temperature derivative along the normal vector to the cylinder surface).
  I couldn't calculate the temperature derivative by using the expression tab in CFD-Post, i put the expression as follows: "Temperature.Gradient R @cylinder wall "
  but it gives me the following error: "The following unrecognized name was referenced: Temperature.Gradient R"
  
  P.S. i identified another variable "R" and its expression is sqrt(X^2 +Y^2) and i created a polyline at the cylinder surface and named it "cylinder wall"
  
  Thank you!
- December 11, 2019 at 10:56 am
  
  Rob
  Forum Moderator
  
  Try getting the output of Temperature.Gradient @cylinder wall and see what happens. As a more general comment, I mostly use _ and never a "space" when setting up models, expressions etc. Probably not needed any more, but was critical when I started using the software: it does mean I miss some issues!
- December 11, 2019 at 3:17 pm
  
  DavidB7
  Subscriber
  
  Hello Rwoolhou,
  
  Thank you for replying!
  Unfortunately, I tried this expression as well and got this error: "The following unrecognised name was referenced: Temperature.Gradient."
- December 11, 2019 at 4:26 pm
  
  Rob
  Forum Moderator
  
  If you've come from Fluent have a look at Custom Field Functions and also the Thermal & Wall post-processing options. Check Temperature.Gradient exists too: it may not be defined in Post.
- December 18, 2019 at 2:49 am
  
  DavidB7
  Subscriber
  
  Hello Rwoolhou, i checked and i couldn't find it. However, i created an expression to calculate the local nusselt number and it worked fine for the steady state linear conditions.
  I wanted to ask another question; can i ask here or should i make another post?
  
  Thank you for your help!
- December 18, 2019 at 11:58 am
  
  Rob
  Forum Moderator
  
  Another thread please: makes it easier to track.
- December 24, 2020 at 1:02 pm
  
  MahmoudHI
  Subscriber
  
  Hello David,ni would like to ask you about the expression you used in finding the local Nusselt No. nyour clarification will be highly appreciated. Since I'm currently working on a similar problem where I have a fluid flowing into a horizontal tube with a uniform heat flux applied to the tube wall. n