[m_zanichelli]

Dear all,

I am writing this post to ask for some advice regarding a project I have been working on for the last few weeks. I am trying to simulate the inviscid transonic flow around a RAE2822 airfoil at the following conditions (following a NASA testcase: "RAE 2822 Transonic Airfoil: Study #4"):
Ma = 0.729
AOA = 2.31°

Since I will need to try several geometries and computational time saving will be my first objective, I am neglecting viscosity and I am solving Euler Equations. I am doing this with rhoCentralFoam (which, as far as I know, has the inviscid option triggered by setting mu=0).

Since the solution is explicit, I am not getting residuals during calculation (they're automatically equal to zero) and I would like to assess convergence by reaching a plateau of the aerodynamic coefficients, ending the simulation when the value of the drag coefficient stops to change.

The results I've been obtaining seem promising, since after a few minutes I am getting a flowfield that is quite similar to the reference one, and the pressure coefficient behaviour along the chord is quite similar as well as the NASA one, as I am showing below.

cp_conv_plot.jpg

The main problem I am having is that I cannot reach a stable convergence in the aerodynamic coefficients, after 3/4 minutes of physical time they start having a reasonable value (even though the Cd is quite overestimated) but this value oscillates a lot, around the 15/20% of its value. I tried to solve this problem by changing the boundary conditions on the pressure outlet, as I've read that some are more stable than others and I've tried in particular the wavetransmissive bc. I have also tried to change the fvSchemes to use a more dissipative setup and also tried reducing the grid dimension. Nothing seems to work and I would like to ask if somebody has some suggestions about this problem, since I am running out of ideas currently.
I am then attaching my configuration folders so that you can see what I am working on.

https://drive.google.com/file/d/1Zy2...ew?usp=sharing

Please feel free to post any ideas/suggestions