| The flow about slender, pointed bodies can be characterized by different states with angle of attack. At moderate-to-high angles of attack (α ≈ 40°), a steady, asymmetric vortex pattern develops along the body, leading to a net lateral force. At higher angles of attack (α ≈ 60°), the aft-end of the body develops an unsteady von Kármán shedding. As the angle of attack approaches 90°, the entire body length exhibits a time-dependent vortex shedding pattern. The current work develops numerical methods capable of simulating both the steady and unsteady vortex shedding about slender bodies at sub-scale (low Mach number, high laminar Reynolds number) test conditions. At these conditions a large database of experimental and numerical results exists for asymmetric vortex shedding. Emphasis is placed upon minimizing the computational cost for simulating three-dimensional, unsteady vortex shedding without sacrificing accuracy. Requirements for the crossflow resolution, time integration, and viscous stress modeling are developed. These methods are utilized to examine the physical mechanisms involved in flows about pointed bodies at angle of attack. The development of an asymmetric vortex pattern via a convective instability mechanism is investigated using tip bumps, surface roughness, and tip curvature. A model for the initiation of an asymmetric flow state from tip perturbations is presented. The development of Von Kármán shedding on a semi-infinite pointed body is also studied. Numerical experiments are performed to determine whether the region of unsteady shedding on the aft-end of a body at angle of attack stems from a convective or absolute instability of the flow. The interactions between the regions of steady, asymmetric and unsteady von Kármán vortex shedding are examined. |
