A Numerically Tolerant Formulation of the Amplification Factor Transport Transition Model

Modeling instabilities behind laminar-to-turbulence transition is an important component of constructing a complete picture of fluid behavior in the boundary layer. The Reynolds-averaged Navier–Stokes (RANS) equations can be used to quickly obtain approximate flow solutions, but closure of these equations requires modeling choices to account for turbulence and transition. While obtaining approximate solutions of fully turbulent flow has been successfully enabled by various models, the incorporation of laminar-to-turbulent transition for RANS still presents modeling and computational challenges. The amplification factor transport (AFT) model offers a physically motivated description for transition but uses a formulation of a local shape parameter that leads to numerical challenges. This work presents an alternative formulation of AFT based on a new local shape parameter that is more numerically tolerant. New correlation functions are also obtained, and the model is demonstrated for three wedge flow cases. Lastly, the NLF(1)-0416 airfoil is used to highlight outstanding issues with implementing the model on curved geometry.