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Boundary Layer Segmentation on Sharp Highly Swept Leading Edges and Its Effects on Secondary Vortices,
POLITECNICO DI MILANO (ITALY)
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In lifting conditions, the vortical flow on a sharp highly swept leading edge is characterized by a strong adverse pressure gradient acting from the centerline of the wing towards the leading edge, which produces boundary layer separation. A secondary vortex grows and brings to lift loss and to drag rise. The reduction of this secondary vortex may be obtained by means of a slot, which divides the boundary layer in two parts, as in usual slotted flaps. In the present work, the effect of a single slot on a delta wing model has been investigated experimentally, in order to verify the correctness of the basic principle of operation. In the first part of this research, pressure measurements have been performed on an unslotted delta wing model, which enabled to determine the location of the secondary separation line, as a function of the angle of attack. A slotted delta wing model was then built and tests were carried on, showing a remarkable shift of the location of th secondary separation line. In addition, the secondary vortex flow was investigated by means of a tracing gas technique, based on the injection of Helium on the upper surface of the wing and measurements of its concentration in the flow downstream. As a conclusion, boundary layer segmentation appears to be useful tool in preventing large secondary separations and allows higher lift coefficients to be obtained. It is reasonable to suppose that results similar to those reached for this delta wing could be expected also for conventional highly swept wings. Author
APPROVED FOR PUBLIC RELEASE