Integration of the transition model with IDDES

[BumseokLee]

This is a draft pull request for integrating the transition model with IDDES.

The integration is based on a journal paper co-authored by researchers from DLR, University of Cambridge, and University of Birmingham (https://arc.aiaa.org/doi/full/10.2514/1.B39344). In the work, the intermittency is simply applied to the source terms of the k transport equation in the SST IDDES model. Additionally, the authors used a new length scale. However, in the current work, I just used the original length scale of the IDDES model.

For the implementation, I created a new node kernel for the k transport equation, similar to the separate node kernels for DES and IDDES, but didn't make any change in the transition model’s node kernel.

Validation has been conducted for two cases:

• 3D S809 at Re = 1M, AoA = 0~20°, a canonical airfoil case for transition model validation.
• 3D NACA0012 at Re = 2M, AoA = 0~90°, a canonical airfoil case for IDDES validation.

For reference, I've attached the results for the 3D NACA0012 airfoil. Interestingly, neither IDDES nor the transition simulations accurately capture the stall inception, showing in over-prediction of the lift around AoA=20deg. However, IDDES better predicts the lift in deep stall regimes (AoA >=30 deg) than the transition model alone, and the transition model with IDDES exhibits very similar behavior to the IDDES in these conditions. For the drag, the transition model with IDDES captures the drag at deep stall regimes as well as the laminar drag bucket at low angles of attack, better fowlloing the experimental data than either the transition model or IDDES alone.

The Next steps are:

- Create regression test & Unit test
- Documentation

[marchdf]

Looks good! And your todo list looks good as well ;)