how to set Neumann boundary condition for a UDS in Fluent

- March 10, 2019 at 3:16 pm
  
  qooin
  Subscriber
  
  I added a UDS in Fluent. Now I want to set the gradient of the scalar at the domain boundary as zero(say, outflow boundary condition). how can I set it? which UDF macro does it need?
  
  Thank you in advance for your help.
- March 10, 2019 at 3:51 pm
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  Zero flux is zero gradient. No UDF is required.
- March 11, 2019 at 3:07 am
  
  qooin
  Subscriber
  
  Thanks for your reply.
  
  You mean set specified flux to zero in the boundary condition dialog box? But there is no diffusion term in my UDS equation;The diffusion coefficient is zero. Does this way work in my case?
- March 11, 2019 at 5:58 am
  
  Amine Ben Hadj Ali
  Ansys Employee
  
  Yes: zero flux is equal to zero gradient at boundary.