Industrial view on transition prediction

We assess linear, local and non-local, as well as non-linear instability theory for transition prediction. After an overview of all linear, local theories, we re-evaluate the transition experiment with the HQ26 profile using non-local theory and obtain an improved N-factor correlation. We propose a hybrid two-N-factor method, using local theory to model the Tollmien-Schlichting instability and non-local theory for the cross-flow instability. Furthermore, we report on our experience applying nonlinear theory to the VFW614/ATTAS and Fokker 100 flight tests. We show that there is no standard initial amplitude for Tollmien-Schlichting dominated transition and that saturation scenarios occur in cross-flow dominated transition.