A transition prediction model for boundary layers subjected to free-stream turbulence

The modifications of the mean and fluctuating characteristics of laminar boundary layers subjected to free stream turbulence (FST) are investigated numerically. In the region upstream of the transition onset, the fluctuations inside the boundary layer are dominated by elongated structures growing downstream in amplitude. These streaky structures, also called Klebanoff or breathing modes, are crucial to the transition process. A linear and parabolic approach, inspired by the hydrodynamic stability theory, is used to describe the streaks dynamic. The model is then applied to predict the transition position. The results are compared to experimental data, with various boundary conditions, including ERCOFTAC test cases.