MRF and transient solution

- September 17, 2019 at 4:55 pm
  
  cs437
  Subscriber
  
  I would like to know what theory it is associated with MRF and transient solution. Typically, MRF is a steady-state approximation; however, many papers use MRF to do transient simulation. How different between transient MRF and sliding mesh? Is it able to capture flow behaviors as time-dependence as sliding mesh? If not, what is the reason to do the transient simulation with MRF approach? Is anyone give me a clear explanation or some available sources.
- October 2, 2019 at 7:55 pm
  
  wcao
  Ansys Employee
  
  Hi,
  
  Seems your question can be grouped into three aspects:
  
  1. Available source for MRF and Sliding Mesh: Please refer to the Theory guide of Fluent for the version you are using. You can access them via any help button in Fluent software. The MRF and Sliding (Dynamic) Mesh are usually in Chapter 2 and 3. As for the papers you mentioned using MRF to do transient simulation, they should provide some justification for their methods. If no, you can ask the author directly.
  
  2. Comparing the steady and transient MRF, if your problem is intrinsically transient, you will need a transient solver. For example, if you would like to apply MRF along with LES in Fluent for to resolve vortex structure in some turbulent flow, you must have 3D transient set up.
  
  3. Comparing the sliding mesh and transient MRF, if the static zone is open field, such as for wind turbine simulation, there will be no large difference between the two difference; However, if it is in a centrifugal compressor, you imagine that the relative location of the rotor and stator is keep changing in Sliding Mesh, which can not be represented in MRF. So when the relative location of the moving wall and static wall maters, there might be significant difference between transient MRF and Sliding Mesh.
- November 7, 2019 at 3:46 am
  
  cs437
  Subscriber
  
  Hi,
  
  Thank you so much for the clarification. My problem is dealing with 3D mixing tank with vortex. Based on your reply #2, it means I am able to use MRF in a transient simulation using LES as a turbulence model, right? In addition, could I do sliding mesh with non-conformal mesh? since it is better in terms of mesh quality when I did the meshing.
  
  Best regards,
- November 7, 2019 at 6:37 am
  
  DrAmine
  Ansys Employee
  
  Yes for both questions. Transient MRF for mixibg tank is food compromise. Superior is only sliding mesh ansatz.
- February 19, 2020 at 4:53 pm
  
  cs437
  Subscriber
  
  Hi,
  
  How do I decide that I need conformal mesh OR non-conformal mesh in MRF approach?
- February 19, 2020 at 4:57 pm
  
  Rob
  Forum Moderator
  
  Can you assume the pressure & velocity won't change if you run the rotating part in different positions? Eg blade-baffle interactions in a mixing tank.
- February 20, 2020 at 1:55 am
  
  cs437
  Subscriber
  
  Hi,
  
  Yes, it won't change.
- February 20, 2020 at 1:56 pm
  
  Rob
  Forum Moderator
  
  Then reference frame is suitable.
  
  You can now explain why based on having read the manual.