Experimental Investigation of Separated Shear Layer Over a Flat Plate for Various Angles of Attack and Tail Flap Deflections

Shear layer development over a thick flat plate with a semi-circular leading edge is investigated for a range of angles of attack under different imposed pressure gradients for a Reynolds number of 2.44×10⁵ (based on chord and free-stream velocity). The features of the separated shear layer are very well documented through a combination of surface pressure measurement and flow visualization by particle image velocimetry (PIV). The instability of the separated layer occurs because of enhanced receptivity of perturbations leading to the development of significant unsteadiness and three-dimensional motions in the second-half of the bubble. The onset of separation, transition and the point of reattachment are identified for varying angles of attack and imposed pressure gradients. The reattachment point shifts from 12.5% to 53% of chord resulting in enhancement of bubble length from 5% to 47%, while onset of transition shifts upstream from 14% to 7.5% as α increases. The Reynolds number based on the length of laminar shear layer is found to be in the range of 0.7×10⁴ to 2.0×10⁴. The separated shear layer fails to reattach attributing to bubble bursting at α = 12° for β = −45°, while, it bursts at α = 5° for β = +45°. The bubble falls in the category of short bubble for α < 3°, whereas, it becomes long for α ≥ 3°. The data concerning laminar portion and reattachment points agree well with the literature.