Overview of the AFT Model for Transition Prediction in Complex Aerodynamic Flows

For many aerodynamic flows of practical interest, prediction of laminar-turbulent transition from first principles is a difficult, if not impossible, undertaking. These flows are often characterized by high Reynolds numbers, geometric complexities, and inherent unsteadiness, which limits the ability to perform direct numerical simulation of the transition processes or to perform detailed stability calculations against a base flow. In response to this and other flow simulation needs, there has been increased interest by the aerodynamics community in PDE-based transition models. Such models are generally phenomenological in nature and designed to estimate the path to transition using single-point correlations. The practical benefits of such models are that they can be fully integrated within a flow solver without an excessive increase in grid resolution requirements or sacrificing parallelization, and they can be applied to general three-dimensional configurations with minimal user intervention. An overview of these PDE-based models is provided, and, in particular, the amplification factor transport (AFT) model developed by the author. The AFT model is rooted in linear stability theory and it has been successfully applied to a wide range of engineering applications. The model formulation is discussed, and key results are included highlighting the model’s predictive capabilities.