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Type of Document	Dissertation
Author	Laurence, Stuart Jon
Author's Email Address	stulaurence AT gmail.com
URN	etd-04242006-172719
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-04242006-172719
Title	Proximal bodies in hypersonic flow
Degree	PhD
Option	Aeronautics
Advisory Committee	Advisor Name Title H. G. Hornung Committee Chair Dale I. Pullin Committee Member David John Stevenson Committee Member Joseph E. Shepherd Committee Member Tim Colonius Committee Member
Keywords	blast wave analogy hypersonic force measurement aerodynamic interactions meteoroid fragmentation
Date of Defense	2006-02-04
Availability	unrestricted
Abstract The problem of proximal bodies in hypersonic flow is encountered in several important situations, both natural and man-made. The present work seeks to investigate one aspect of this problem by exploring the forces experienced by a secondary body when some part of it is within the shocked region created by a primary body travelling at hypersonic speeds. An analytical methodology based on the blast wave analogy is developed and used to predict the secondary force coefficients for simple geometries in both two and three dimensions. When the secondary body is entirely inside the primary shocked region, the nature of the lateral coefficient is found to depend strongly on the relative size of the two bodies. For two spheres, the methodology predicts that the secondary body will experience an exclusively attractive lateral force if the secondary diameter is larger then one-sixth the primary diameter. The analytical results are compared with numerical simulations carried out using the AMROC software and good agreement is obtained if an appropriate normalization for the lateral displacement is used. Results from a series of experiments in the T5 hypervelocity shock tunnel are also presented and compared with perfect-gas numerical simulations, again with good agreement. In order to model this situation experimentally, a new force-measurement technique for short-duration hypersonic facilities has been developed, and results from the validation experiments are included. Finally, the analytical methodology is used to model two physical situations. First, the entry of a binary asteroid system into the Earth's atmosphere is simulated. Second, a model for a fragmenting meteoroid in a planetary atmosphere is developed, and simulations are carried out to determine whether the secondary scatter patterns in the Sikhote-Alin crater field may be attributed to aerodynamic interactions between fragments rather than to secondary fragmentation. It is found that while aerodynamic interactions lead to increased secondary crater grouping, these groups do not exhibit the typically elliptical shape that we would expect secondary fragmentation to produce.
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