Laminar separation bubble bursting and formation on a finite wing in an unsteady freestream.

The transient dynamics of laminar separation bubble formation and bursting on a cantilevered NACA 0018 finite wing model with an aspect ratio of 2.5 and an angle of attack of 6° is studied experimentally in a wind tunnel. Bubble bursting and formation are induced by a change in the freestream velocity that changes the chord Reynolds number between limiting values producing either a long or short bubble under steady state conditions. Time-resolved direct force measurements are employed to characterise the transient response of global lift and drag forces to bubble bursting and formation. Simultaneous with force data acquisition, stereo particle image velocimetry is performed in a series of planes on the suction surface of the wing to link the unsteady loading to the transient development of the separation bubble and quantify the influence of unsteady wing tip and wing root effects on the bursting and formation processes. The results provide novel insight into the dynamics of bubble bursting and formation on a finite wing and the associated changes in aerodynamic loading.