Low Speed Canard-Tip-Vortex Airfoil Interaction

This paper describes a series of ongoing experiments to capture the details of perpendicular vortex-airfoil interaction. Three test cases explored are: 1) a 21% thick symmetric airfoil at 1.1° angle of attack, 2)a thin flat plate of 2.5% thickness with rounded leading edge, sharp trailing edge and zero angle of attack and 3) A 12% thick symmetric airfoil at zero angle of attack. The tip vortex was generated by a NACA0016 wing at 5° AOA. The strength of the vortex was computed from the velocity profile measured upstream for the first two cases. Pressure measurements on the 21% airfoil were used to quantify the effect of the vortex as a function of its stand-off distance from the airfoil. Vortex trajectories over the airfoils were obtained from laser sheet videography. The vortex motion conforms to potential flow expectations except in regions of pressure gradient and during head-on interaction. When the generating wing is moved continuously across the airfoil there is a time lag between wing and vortex motion. The vortex switching from the top to the bottom surface is initiated by the splitting of the primary vortex into two and occurs in a short period of time. This is a source of unsteady effects on the interacting airfoil and a vortex jump parameter is defined for the switching process. Issues regarding symmetry in the motion above and below the airfoils are discussed.