On Controlling the Path & Structure of a Leading-Edge Vortex by a Single, Small Jet

The flow over a straight and a cranked lambda wing planform having a flat upper surface, and a sharp leading edge was investigated experimentally, using flow visualization and particle image velocimetry, while measuring the forces and moments on the model. A single steady jet located just inboard of the crank provided the wing with nose up or down pitch control authority and enabled the wing to be trimmed at high angles of incidence. To achieve this result the jet was rotated at various angles relative to the oncoming free stream therefore disrupting the feedback mechanism existing between the primary leading-edge vortex and the separated shear layer that feeds it with vorticity. In the absence of a crank, this feedback is provided by the vortical layer (secondary vortex) that is forced upward by the primary vortex and is entrained into the separated shear layer. In the presence of the crank, a new vortex created downstream of a crank serves a similar purpose as the shear layer. The experiments were carried out in a low-speed wind tunnel at 25 meters/second therefore providing a Reynold number of approximately 1.2 x 106 and a Mach number smaller than 0.1.