Tripping device effects on the turbulent boundary layedevelopment

Tripping devices are commonly used in wind tunnel testing to hasten the boundary layer laminar-turbulent transition and mimic aerodynamic effects present in full-scale applications. However, the tripping device role in the transition process and in the developed turbulent boundary layer is still not fully understood. This paper discusses the interplay between the geometry of tripping devices and the development of a turbulent boundary layer at the airfoil trailing edge. Experiments were performed in the Aeroacoustic Wind Tunnel of the University of Twente. The tripping devices investigated were zigzag strips and randomly distributed grits installed in a NACA 0012 at zero angle of attack. The tripping device heights ranged from 25% to 191% of the undisturbed boundary layer thickness. Hot-wire measurements were performed to evaluate the boundary layer development at different chordwise positions, including close to the trailing edge. This paper shows that the trip height strongly affects the transition process and the characteristics of the turbulent boundary layer at the trailing edge, e.g., boundary layer thickness and shape factor. Furthermore, the increase of the trip height results in a level increase of the boundary layer velocity spectrum for low frequencies. The type of tripping device influences the boundary layer development; however, it does not play a role in the characteristics of the turbulent boundary layer at the trailing edge.