Investigation of Cross-Flow and Laminar Separation Using Infrared Thermography

An experimental investigation has been conducted to explore boundary layer development along the suction side of a modified NACA 643-618 airfoil at a variety of angles of attack (a) and chord based Reynolds numbers (ReC) for different sweep angles (T). Characteristics of the laminar separation bubble (LSB) that develops on this airfoil were obtained through static pressure measurements and infrared thermography (IT). For low Reynolds numbers (ReC = 200, 000) across T = 0°, 35°, 45°, both measurement techniques detect a negligible influence of sweep angle on LSB behavior, aligning with literature. At negative a and increased Reynolds number, noticeable stationary spanwise periodic structures (crossflow vortices) are detected by IT for T = 45°. The onset of spanwise periodic structures depends on the angle of attack and Reynolds number. Significant negative a are necessary for visualization at low Reynolds numbers (a ≤ −5° at ReC = 400, 000). At the highest tested Reynolds number (ReC = 600, 000), stationary crossflow are observed for a ≤ 0°. Strong indication of pure crossflow dominated transition is observed at the lowest tested angles of attack (a ≤ 8°, T = 45°, ReC = 600, 000). The dominant spanwise wavelength varies slightly across conditions, but is found relative to the chord at Yzc = 1.25%. The parameter space includes conditions resulting in LSB transition, stationary crossflow in the presence of LSB, and crossflow transition at several Reynolds numbers.