Effect of Controlled Imperfections on the Vortex Asymmetry of a Conical Body

Abstract

Flight vehicles with pointed forebodies experience large side forces and yaw moments at high angles of incidence due to random surface imperfections. These adverse side forces and yaw moments are the results of asymmetric vortices on conical bodies. To better understand the underlying flow physics associated with slender cones at high angles of incidence, an experimental investigation was conducted on a conventionally machined and a highly polished cone at subsonic speeds. Measurements included force and moments and velocity field using particle image velocimetry. Force measurement results show that the side-force magnitude and its dependence on roll orientation can be significantly reduced by polishing the cone surface. The results indicate that the ratio of imperfection height to the local crossflow boundary-layer thickness is a pertinent parameter influencing the location and growth of vortices. The region of incipient boundary-layer separation was found to be very sensitive to the presence of surface imperfections. By judiciously selecting the size and location of surface imperfections, significant changes can be made to the entire flowfield. Simultaneous force and time-resolved velocity measurements elucidate that the vortex switching with roll orientation for a cone at a high angle of incidence is a gradual process.