Study of 2D and 3D Boundary Layer of Moving Walls by Embedded LDV measurements

摘要

The present final report concerns the extension of the seed contract to more new 2D and 3D tests in order to provide the Aeromechanics of the Army/ NASA Rotorcraft Division with experimental results on BL velocity profiles and on the structure of unsteady separated 2D and 3D flows. Smoke visualization and embedded laser velocimeter (2D and 3D) operating in the backscatter mode were used to survey the separation bubble and the flow about 2D and 3D wings oscillating in the wind tunnel S2Luminy. The experiments were carried out about two rectangular wings with a NACA 0012 airfoil section oscillating in pitch one spanning the entire test section (2D configuration) the other only the half section (3D configuration). During the oscillation the wing angle of attack varied around mean values alpha 0 = 6 deg and 12 deg through an angle amplitude delta alpha = +/- 6 deg at reduced frequency kappa = 0.188 and at nominal Reynolds numbers R(sub e) = 10(sub 5). The measurements of 2 and 3 orthogonal components of instantaneous velocity through the boundary layer along a normal to the surface of the wing have shown that the embedded 2D and 3D laser velocimeters are well suited to characterize qualitatively and quantitatively the structure of the boundary layer (laminar transition turbulent turbulence intensity and Reynolds stresses) as well as strong separation with leading edge bubble involved during dynamic stall. Geometry and behavior of the separation bubble on the upper side of the airfoils were investigated from velocity profiles. These results constitute a useful database for future computational unsteady boundary layer.