There are two main objectives of this work: (1) to determine if and how the presence of a forward-facing axial cavity in a blunt nose can reduce surface heating rates compared to a blunt body without a cavity, and (2) to describe the fluid dynamics of these unsteady flows. A commercial finite-volume computer code was used to produce steady and unsteady time-accurate numerical simulations. Numerical simulation results were often directly compared to recent experiments.; The initial study focused on the surface heating and flowfield structure of steady cavity flows. Sharp lips were found to produce both a recirculation region which 'cools' the outer surface, and severe heating just inside the cavity. Rounding the lip eliminates the recirculation region and alleviates heating inside the cavity. It was concluded that the steady cavity flow does not present a surface heat reduction compared with blunt nose shapes.; Subsequent study focused on unsteady cavity flows. A new nose-tip surface heat reduction mechanism was discovered. Substantial surface nose-tip cooling is achieved by creating strong longitudinal pressure oscillations within the cavity to induce large bow shock oscillations. Due to the motion of the bow shock relative to the body, the mean stagnation temperature of the air flow into the cavity is reduced. The cooling benefit increases with mean bow shock oscillation. This mechanism has been further validated by experiment. The cooling mechanism is not effective in very deep cavities since the bow shock exhibits only long period oscillation. The design implications of using a nose-cavity for surface heat reduction in a hypersonic penetrator are briefly addressed.; A parameter study was conducted to study the mechanisms of resonance. Resonant pressure oscillations within the cavity occur for relatively shallow cavities provided freestream noise is present. However, deeper cavities self-sustain strong resonance. A spring-mass-damper model is described which emulates noise-driven, relatively shallow cavity acoustic behavior. An extensive parametric study of relatively-shallow cavities driven by freestream noise was conducted to better understand the unsteady fluid dynamics and verify the spring-mass-damper model.
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