Abstract
The use of leading edge with different geometrical patterns will affect the development of boundary layer flow on a flat plate and its heat transfer properties. In this work, the effects of three patterns namely saw-tooth, semicircular and slots with same wavelength and amplitude were examined. The experiments were carried out for Reynolds number based on wavelength of patterns ranging from 1540 to 3850. For all cases, after each valley, an oval shape region was formed containing a counter- rotating vortex pair. It is also shown that for the flat plate with slots, another vortex was visualized between each valley.
Highlights
A method to improve the aerodynamic performance of airfoils, that is, to increase lift and/or reduce drag is by momentum exchange and separation delay
Despite interesting results such as the occurrence of a mixing zone [2] and suppression of von Karman vortex street in the wake of an airfoil [3], vortex generators introduce additional drag in flow which is not desirable for stall suppression. Another technique of generating such streamwise vortices in boundary layer is to use leading edge patterns. This idea of leading edge pattern was inspired by nature, for example, it was observed that owl wings generate mini vortices by comb like feathers, so to retard the boundary layer separation, and give this predator the ability of quietly approaching the prey by high stall angle of attack [4]
Visualization results were obtained at some streamwise positions (x) from the flat plate leading edge at different Reynolds numbers ranging from 1540 to 3850 which correspond to the flow velocities ranging from 1.5 to 3.75 m/s
Summary
A method to improve the aerodynamic performance of airfoils, that is, to increase lift and/or reduce drag is by momentum exchange and separation delay. Vortex generators are well known devices which are used to generate either co-rotating or counterrotating chordwise wise vortices through making discontinuities and shear force [1] Despite interesting results such as the occurrence of a mixing zone [2] and suppression of von Karman vortex street in the wake of an airfoil [3], vortex generators introduce additional drag in flow which is not desirable for stall suppression. Another technique of generating such streamwise vortices in boundary layer is to use leading edge patterns. This idea of leading edge pattern was inspired by nature, for example, it was observed that owl wings generate mini vortices by comb like feathers, so to retard the boundary layer separation, and give this predator the ability of quietly approaching the prey by high stall angle of attack [4]
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