Two-Way FSI: Fluent Not Converging

Hi all.

For reference I am using ANSYS 2020 R1 with a student license.

I am attempting a Fluid Structure Interaction simulation on a simplified rocket fin with 1 degree angle of attack at Mach 2. I am new to using Fluent so I suspect there may be issues regarding the setup, I have not found a good tutorial which covers everything I need to do for my version of ANSYS, the best I have come across is for version 18, and the simulation is not exactly the same as what I am doing.

I've finally got around the errors I was running into regarding size limits, but now I am experiencing non-convergence of my Fluent fluid flow system. According to the Solution Information window, the structural system converges. I am also not sure how the Fluent post-processing works.

I'm running the System Coupling for 1s with a step size of 0.1s and maximum iterations set to 20. Ideally, I would like to simulate at least a few seconds, but I'd also prefer not to have a simulation that takes upwards of a few hours to run, my current setup takes over an hour, and that's with running Fluent with all 6 of my CPU cores. Does anyone have any tips? I have attached the .wbpz file to this post, it gave me a warning that some files may need repair, I'm not exactly sure what that means.


Answers

  • sdebsdeb Forum Coordinator

    Hello,

    I would recommend you to first test your Fluent Model alone without any FSI or System Coupling.

    As you mentioned, the Mach number in this model is quite high around 2 or more.

    Do you observe normal or oblique shock waves forming near the airfoil?

    What are the material properties and the solver controls? Are you using Pressure based or Density based solver?

    Now a days, Pressure based solver is also capable of solving a high Mach number flow but Density based might be more appropriate to capture shocks.

    Also check the mesh resolution and make sure it is consistent with the turbulence model that you are using.

    Once you validate the Fluent results alone for a constant angle of attack, then you can try to couple the Mechanical to Fluent using SC.

    Regards,

    Surya

  • Hi Surya, you make a good point to put some more work into convergence of the Fluent model alone, I think that's probably my best path forward for now.

    Unfortunately, I don't think I know enough to answer your questions very well. This project was not started by me; someone previously studied one-way FSI and taught me how to set it up using CFX and Static Structural, then it has been my responsibility to translate these settings into a two-way simulation. I chose the pressure based solver, though I don't know about shock waves forming near the airfoil. Do you know where I could learn more about this to determine what fits for my project? I don't have much time, it's a one-semester fourth year project for me.

    Thanks,

    Simon

  • sdebsdeb Forum Coordinator

    Hello Simon,

    You should be able to get relevant information from internet as I am sure you will have several good quality information on compressible flows involving high Mach numbers.

    You can also take a look at the following compressible flow physics link from Fluent.

    I hope this helps.

    Regards,

    Surya

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