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Asymmetric Vortex Control on Slender Bodies at High Angles of Incidence


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The phenomenon of vortex asymmetry has been observed over pointed forebodies at high angles of incidence. This problem is essentially predominant at low to moderate subsonic speeds, a regime in which high-alpha maneuvers normally occur. At a small incidence angle (typically less than the semi-apex angle of the conical body), the crossflow boundary layer remains attached to the surface. When the angle of incidence is increased(while still below the cone apex angle), a steady symmetric vortex pair appears in the wake region of a slender conical body. Further increasing the incidence angle (greater than the nose apex angle) results in vortex asymmetry and large magnitude of side forces and yaw moments. The yaw moments are too large to be controlled using a rudder in military aircraft and control surfaces in the case of a missile. The flow over a long slender body is very complex in nature and involve the evolution of multiple vortex pairs. The development of the flow-field can vary between studies due to the sensitivity to small scale surface imperfections. The ratio of imperfection height to the local boundary layer thickness is a critical parameter in determining the initiation and growth of vortices. On the other hand, if the surface imperfection size exceeds the boundary layer significantly, such as for protrusions, it can considerably affect the aerodynamic loads of the vehicle. The main objectives of the study were to improve our understanding of the source and the nature of vortex asymmetry on slender cones at high angles of incidence.



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