Transition on a high-lift swept wing in the European project EUROLIFT

Performance of transport aircraft in high-lift conditions is directly related to the maximum lift. However, most of the high-lift tests are carried out at subscale conditions, and performance is then derived by extrapolation to flight Reynolds number. So-called adverse Reynolds number effects (sudden decrease of maximum lift with increasing Reynolds number) often occur when extrapolations from the wind-tunnel and flight-tests results are compared. Most of these effects are due to changes in the transition process. Improvement of the knowledge of the transition process for three-dimensional high-lift configurations is, thus, necessary. Therefore, specific experimental and numerical tasks were decided on within the European research project EUROLIFT, dedicated to high-lift aerodynamics. Within this program, a generic high-lift swept wing was first tested by the use of wall hot films and infrared thermograpby in the ONERA F1 pressurized wind tunnel to study Reynolds number effects on transition. This test campaign provided a detailed database for the transition prediction tools developers and for the assessment of numerical methods. Based on accurate pressure distributions obtained from three-dimensional Navier-Stokes computations, a theoretical and numerical study of transition was conducted based on both exact and simplified stability approaches. Results contributed to a better understanding of transition phenomena in high-lift conditions, as well as to extension of the validity of methods and rules used to predict attachment line contamination, relaminarization, and stability-based transition.