Experimental Investigation of Vortex Dynamics on a 65deg Delta Wing

The flow structure on the upper side of a delta wing is extremely complex. At moderate angle of attack the flow field is dominated by organized vortical flow structures emanating from the leading edge. The pressure distribution created on the wing surface by these leading edge vortices causes an increment of lift, that may be a relevant percentage of the total wing lift, depending on sweep angle. Delta wing performance is conditioned, however, by a phenomenon known as vortex breakdown or vortex bursting, that appears at high angle of attack. This leads to a drastic change in the flow field which influences the trend of the aerodynamic coefficients. With the aim of giving a contribution to the understanding of the phenomenon of vortex breakdown, a 65° delta wing has been extensively tested in the low speed wind tunnel of Politecnico di Torino both in static and dynamic conditions. Many experiments have been carried out in an effort to understand the factors which can affect the breakdown by varying angle of attack, sideslip angle and Reynolds number. Flow visualizations have been performed using helium bubble tracers. This technique showed a very good capability for visualizing vortical flows and breakdown, both in static and dynamic conditions. For the static case, pressure distributions are presented, correlated to force measurements and flow visualizations, at different angles of attack and sideslip, for different flow conditions. For the dynamic case, force measurements are shown, compared with flow visualizations, for different angles of attack and for different oscillation frequencies. Finally, surface flow was also investigated in steady flow conditions by means of IR thermography in order to gain some new insights into the correlation between separation and boundary layer transition.