Session G16: Aerodynamics: Airfoils, Wings and Bodies

Effect of Thickness-to-Chord Ratio on Flow Structure of Nonslender Delta Wing

The effects of thickness-to-chord (t/C) ratio on flow structures of nonslender delta wings with sweep angles of 35 and 45 degrees are characterized in a low-speed wind tunnel using velocity, pressure, and force measurements. The delta wings with t/C ratios varying from 2 % to 19 % are tested at broad ranges of attack angles and Reynolds numbers. The results indicate that the effect of t/C ratio on flow structure is quite substantial. Considering the low angles of attack where the wings experience leading edge vortex structure, the strength of the vortex structure increases as the t/C ratio increases. However, the wing with lowest t/C ratio has pronounced surface separation at significantly higher angle of attack compared to the wing with highest t/C ratio, which indicates that lowest t/C ratio wing might be more resistive to the stall condition. These results are well supported by the force measurements such that high t/C ratio induces higher lift coefficient, C_L, at low attack angles, whereas maximum C_L values that can be reached are significantly higher and appears at significantly higher angle of attack for low t/C ratio wings. Considering the C_L/C_D ratio, increase in t/C ratio induces remarkable drop in C_L/C_D values.   

Vortex Interactions on a Long Slender Body at High Angles of Incidence

A slender body of revolution experiences large side forces and yaw moments due to flow asymmetry at high angles of incidence. The flow asymmetry is characterized by a pair of asymmetric vortices that form near the nose region; interact with each other and the surfaces downstream. The goal of the present experimental study is to better understand the flow physics associated with vortex asymmetry on long slender bodies at high incidence particularly the initiation, growth, and interaction of vortices. Measurements were carried out on a cone-cylinder body of semi-apex angle 12° and slenderness ratio of 8.  Particle Image Velocimetry results show that the vortices which are symmetric over the cone can develop asymmetry at the cone-cylinder junction. The primary counter-rotating vortex pair initiates at the cone-tip whereas several secondary vortices emanate from the shear layer along the cylindrical body and merge with the primary vortex pair. Various stages of vortex merging were captured in the present study on a long slender body at high angles of incidence.