"Experimental Study of Bluntness Induced Structures on a 7⁰ half-angle cone in Hypersonic Flow"

Abstract:

Understanding the dominant transition mechanisms is critical for hypersonic vehicle design. For sharp, axisymmetric, slender bodies, acoustic instabilities know as Mack’s second mode are the dominant path to transition when equipped with a sharp tip. For blunt geometries, which correspond to most practical applications, the dominant transition mechanisms are not yet understood. This research focuses on the flow structures revealed in hypersonic flow over a 7-degree half angle cone at zero angle of attack performed at the Air Force Research Laboratory’s Mach 6 Ludwieg Tube. An initial experiment using simultaneous schlieren flow visualization and surface pressure measurements reveals bluntness induced flow structures differentiated as elongated structures and wisps emerging at different bluntness configurations. While the former structures appear associated to acoustic instabilities, wisps offer no signature in the surface pressure measurements. This conclusion led to a follow-up experiment making use of a colinear FLDI (Focused Laser Differential Interferometry) – Schlieren optical diagnostic method to provide the first experimental analysis of wisp structures.

Biography:

Alexandre Berger completed his Ph.D. at Texas A&M University. His doctoral research was performed at the Klebanoff-Saric Wind tunnel focusing on the fundamental mechanism of turbulent wedge spreading. He was then awarded and NRC associateship to pursue his research in hypersonic boundary layer transition at the Air Force Research Laboratory where his research focus shifted to experimental hypersonic boundary layer transition. As a new faculty at the FAMU-FSU College of Engineering, Dr. Berger expects to continue this research and develop novel flow diagnostic methods for implementation in FCAAP facilities.