Dynamic pitching effect on a laminar separation bubble

• Published in: Experiments in fluids 2015-09, Vol.56 (9), p.1-17, Article 172
• Main Authors: Nati, A., de Kat, R., Scarano, F., van Oudheusden, B. W.
• Format: Article
• Language: English
• Subjects: Aerofoils; Bubbles; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fluid dynamics; Fluid flow; Fluid- and Aerodynamics; Heat and Mass Transfer; Research Article; Rollers; Separation; Shear layers; Three dimensional
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-015-2031-6

The unsteady effect of a periodic pitching motion on the characteristic of a laminar separation bubble on the suction side of a SD7003 aerofoil is investigated by means of time-resolved planar and tomographic particle image velocimetry. The measurements provide information on the separation, transition and vortex roll-up onset as well as the spanwise distribution of vortical structures, for both the dynamic pitching between 4° and 8° and corresponding cases at a static pitch angle. During pitching, a clear hysteresis behaviour is observed for the vortex roll-up position and shedding frequency, showing a strongly delayed recovery of the shear layer with respect to the steady aerofoil case. The development of the shear layer transition exhibits initially 2D Kelvin–Helmholtz rollers that are interrupted, forming Λ-shaped rollers, which eventually evolve into 3D arch-shaped hairpin structures. The 3D analysis of undulated rollers allowed the determination of the rollers streamwise spatial separation for both static and pitching aerofoil cases .