This thesis reports on two new gas dynamical phenomena associated with a bluff body in a hypersonic stream such as a planetary entry configuration.A generalized concept of similarity is proposed through the introduction of the concept of Pi group fields. A set of points, identifiable through distinct flow features, named phenomenological points is defined on the flow fields. While the field concept of the Pi group recovers the traditional Pi group analysis as an instantiation, it provides further insights into the existence of approximate similarities as well as providing insights on the impact of microscopic physics on the macroscopic flow similarity. A set of new theoretical tools are devised including a concept of a metric, the distance between two flow fields, based on Pi group field values at phenomenological points. A representation, named wake energy recovery plot (WERP), indicates to two distinct phenomena in hypersonic bluff body flows: one associated with Mach and Reynolds numbers, the other associated with Prandtl number.A similarity of the hypersonic bluff body flow fields, named near-body asymptotic similarity (NBAS), is identified. CFD corroborations of NBAS provide ostensibly similar near body flows to significantly disparate freestream values of Pi groups. NBAS generalizes the existing scaling laws, such as the binary scaling law, while providing a firm theoretical basis based on the Buckingham Pi theorem.A model for the steady state near wake vortex based on conservation of energy is proposed. The analytical expression derived is scaled by the Prandtl number. The above model predicts higher wake total temperatures, than that of the freestream, when the Prandtl number exceeds unity. The effect is named wake flow thermal inversion (WFTI) and it is corrobo-rated in CFD generated solutions of the Navier-Stokes equations.The new phenomena are a feature of Navier-Stokes (N-S) equations. The theories are also based on the conservation laws scaled by the same kinematic Pi groups that scale the N-S system. While the corroborations of the predictions made by the theories are done on simple, generic CFD generated N-S solution fields; the phenomena are general and underpin all hypersonic bluff body flows.
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