What model to use when having both turbulent and laminar flow simultaneously in simulation domain

- June 3, 2020 at 12:23 am
  
  AlexC
  Subscriber
  
  Please see the figure below. Hope the information is clear.
  
  Now imagine we have flow comes into a larger tube (Tube 1) from left, and then moves into a smaller tube (Tube 2) and exit Tube 2 from the right. By mass balance, we can easily find out that the Reynolds number between Tube 1 and Tube 2 is:
  
  Re1/Re2=D2/D1
  
  So by picking the right D1 and D2, we can easily have laminar flow in Tube 1 and turbulent flow in Tube 2. In this case, what model should we use? Laminar model or turbulent model? It seems neither would work and I couldn't figure out how I should model this problem.
- June 3, 2020 at 3:21 am
  
  Kalyan Goparaju
  Ansys Employee
  
  Hello,
  
  Ansys Fluent has viscous models that are purpose built for computing flows that exhibit laminar-to-turbulent transition. The recommended approach is to select the SST k-w model and turn on 'Intermittency Transition Model'.
  
  Thanks,
  
  Kalyan
- June 3, 2020 at 9:28 pm
  
  AlexC
  Subscriber
  
  Thank you Kalyan! That answers my question!
  
  Best,
  
  Alex