[ssp24]

I am working on an aeroelastic analysis of LE mini spoilers for load alleviation. I have a full size CRM wing case with a mini spoiler placed at 15% chord from LE. I have it coupled with NASTRAN to get a strongly coupled 2 way FSI.



This mini spoiler is modeled as a 0 thickness surface, since my initial thought was that to simulate a mid flight deployment, I have to keep the surface as an 'interior' BC and at the appropriate time, switch to a 'wall' BC.


The problem I have been facing is that the moment I switch the BC type to wall, the simulation becomes unstable, with very long times to even get 2-3 iterations after which it diverges.



I believe, since I am in transonic domain (M = 0.85) and close to supersonic flow at the mini spoiler location, when the wall is suddenly introduced, the sim gets unstable and cant handle the abrupt change.



I have attempted 2 approaches for this, 1 being to set the surface with porous jump BC with decreasing permeability, but the velocity and pressure drop is not enough for the sim to stabilize. Other approach was to split the mini spoilers into sections, and switch 1 section at a time to the 'wall', but the split has compromised the mesh quality really bad, and my BL is not good anymore.



I was wondering if any seniors or experience users could let me know if there are any other approaches to model these pop up spoilers with sufficient stability of the sim. Please let me know if you want to know any other details of the sim.



I have attached a snap of the log with the porous jump approach, which destabilized and my mini spoiler geometry





Thanks