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TITLE: BUBBLES AND HYPERSONICS: IMPROVING CAVITATION MODELING TO INFORM HYPERSONIC VEHICLE DESIGN

ABSTRACT: Hypersonic vehicles can sustain significant damage when they are impacted by atmospheric particles, including raindrops on the scale of 2 mm. Before colliding with the vehicle, these droplets become deformed and can breakup entirely when they interact with the vehicle’s shock wave. Therefore, knowledge of breakup mechanisms in shock-droplet interactions can give valuable information pertaining to the vehicle loading and potential damage. Current literature explores the role of interface instabilities in the droplet breakup, but there is not a clear consensus on what process may be dominating the breakup. Additionally, most of these studies do not consider that cavitation can also occur in the droplet. Cavitation is the explosive growth of air bubbles in the presence of a very low, potentially negative pressure, which occurs in droplets due to internal shock wave reflections. Therefore, this research looks to explore the role of bubble dynamics in shock-droplet interactions, with particular focus on how an initial bubble nucleus (or several nuclei) can impact the droplet breakup process. Towards this goal, the native OpenFOAM solver will first be verified with simplified problems, including bubble dynamics in a free field, bubble dynamics in a cylindrical drop, and a simplified 2D droplet breakup with a single bubble nucleus in the drop. This model will provide some information pertaining to the role of bubble dynamics in droplet breakup, but to capture the more complex phenomena associated with shock-droplet interactions, solver modifications will be necessary. The modified solver will be verified with analytic, experimental, and computational results, and it will be used to model a 2D shock-droplet interaction when there is an initial bubble nucleus in the drop. This model will also be used to study how multiple bubbles can interact with each other and the droplet; a parameter study will explore how changing the initial vapor volume and bubble positions can change the droplet breakup dynamics. Finally, the 2D model will be extended to a 3D model because the spherical droplet will have different internal wave dynamics than the cylindrical one. Additionally, the 3-dimensional model will allow for better capturing of the complex interface instabilities.

COMMITTEE: ADVISOR/CHAIR Professor Sheryl Grace, ME; Professor Emily Ryan, ME/MSE; Professor James Bird, ME/MSE; Professor Michael Kinzel, University of Central Florida Department of Mechanical and Aerospace Engineering