![]() The authors gratefully acknowledge funding from the National Science Foundation, Award #1805776. These results grant new insights into the intelligent design of the modern bird wing and has important implications for aircraft flight control. In essence, the protracted alula, mimicking a canted flap, is a clever way of inducing and stabilizing a LEV on a steadily translating wing inclined to the flow at high angles. The subsequent stabilization of the LEV is the result of root-to-tip spanwise flow in the LEV core of magnitude greater than 80% of the freestream value. The alula, a small thumb-like appendage on a bird wing, is often credited with increasing lift and decreasing the risk of stall during bird flight. LEV formation is the result of the alula scraping spanwise vorticity from the leading-edge shear layer and inducing its roll-up. al·u·lae A small joint in the middle of a birds wing, homologous with the thumb and bearing three or four quill-like feathers. Normally it lays flat on the wing and is hard to see but birds raise their alulas to prevent a stall during slow flight. alula synonyms, alula pronunciation, alula translation, English dictionary definition of alula. We found that the alula induces and stabilizes a robust conical leading-edge vortex (LEV) that sweeps across the outer wing and smoothly merges with the tip vortex. The alula is a small structure located at the joint between the hand-wing and arm-wing of birds and is known to be used in slow flight with high angles of. The alula is the bird’s thumb positioned on the top edge of the wing and covered with three to five small feathers depending on the species. The alula is prominent in birds such as the corvids and almost absent in some soaring seabirds. The alula helps create lift and also prevents stall when a bird comes in for landing. At the center of the front edge of the wing is a structure covered with three to five feathers that functions much like a flap on an airplane’s wing. Using stereoscopic-digital particle image velocimetry we measured the flow over a model wing with and without protracted alulae in a wind tunnel and made volumetric reconstructions of the three-dimensional vortex flow. In the case of the bird wing, the free movement around the joint of the wrist is curtailed so that there is only movement in one plane, preventing the wing from bending up or down during the forces exerted by flight. All flying birds have what’s called an alula on each wing. The recent discovery of leading-edge vortices (LEVs) on the thin hand-wings of some birds suggest that the alula may play a role in LEV formation. When pressure drops on top of the wing, Chiappe explains, the bird automatically lifts the alula, which means it is lifting its first digit. The alula is a small structure present on the leading edge of bird wings and is known to enhance lift by creating a small vortex at its tip. The alula, or bird's thumb, consists of a small set of feathers stationed near the bird's wrist that protract from the wing during slow flight to enhance lift.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |