Laminar-turbulent transition on a cambered naca 16-009 airfoil at low speed

– Infrared thermography, force measurements, and oil flow visualizations are used to investigate the flow patterns around a cambered NACA16-409 airfoil at low Mach number. This cambered profile is widely used for propellers despite the lack of knowledge concerning its flow characteristics. The post-processing of thermograms relies on the analysis of the surface temperature gradient and identification of inflexion points in the temperature distribution. The observations made on the thermograms, based on the distribution of the temperature and Stanton number, are substantiated by the oil flow visualizations. RANS simulations with a transitional SST k-ω & γ turbulence model corroborate the analysis and deliver detailed insight in the flow around the airfoil. Depending on the angle of attack, three distinct flow patterns have been identified: laminar flow with early separation, laminar separation bubble with trailing edge separation, and turbulent flow with trailing edge separation. The shift between the last two regimes occurs sharply. The prediction capability of the transitional RANS simulations and XFOIL in terms of separation as well as reattachment location are compared with the experimental results. The force-coefficients dependency on the angle-of-attack, obtained by experiments, XFOIL, and RANS simulations, bear the traces from these flow patterns.