Experiment on flow mechanism and aerodynamic interaction characteristics of tilt-rotor aircraft

With use of experimental methods, aerodynamic interactional characteristics between rotor and wing of a tilt-rotor aircraft were measured both in hover and transition modes, partly revealing the interactional flow mechanism. The shrinking of rotor downwash was found to be more intense and roll-up vortex was more severe, in its large collective pitch states compared with the small one, based on the result of flow measurement via 3D-PIV (particle image velocimetry) technology. The generation mechanism of “fountain effect” was revealed and the position of “fountain” center influenced by the induced effect of rotor, varied visibly with the changes of collective pitch and the interval between rotor and wing. Then the aerodynamic interactions between rotor and wing in different configurations and state parameters were measured, and during the measurement, tilt-rotors lift was found to be increased either by reducing the vertical or horizontal distances of wind and rotor, bringing to wing the increasing downloads at the same time. A particular configuration at last was selected to perform an interaction experiment in its transition mode to obtain the relationship between the comprehensive aerodynamic characteristics of wing, rotor and the angle of attack of the wing. It is shown that, in large angles of attack of the wing, the encumbering effect of the wing on rotor downwash, acting as a lift-promoting effect on the rotor like “ground effect”, is promoted, but this effect is enervating with the turning of the wing; and the wing lift tends to go up firstly then down with the increase of the wing angles of attack.