Transitional shock wave/boundary-layer interaction unsteadiness on a cone-flare in hypersonic flow

Thesis

The causes of unsteadiness in hypersonic, axisymmetric, and transitional shock wave/boundary-layer interactions (SWBLIs) are investigated experimentally using a cone-flare model in the Oxford High Density Tunnel (HDT). The motivation of this research was to provide accurate measurements of the unsteadiness of transitional SWBLIs and provide a technique for studying such unsteadiness experimentally and numerically. Increasing the field’s understanding of these interactions will improve our ability to predict the large thermal and aerodynamic loading caused by transitional SWBLIs, i.e., SWBLIs in which the boundary layer is transitional. In turn, the design of the thermal protection systems and aerodynamic surfaces of hypersonic vehicles, which inevitably come in contact with SWBLIs in this flight regime, can be refined.

Although the time-averaged characteristics of hypersonic SWBLIs have been studied in detail, transient measurements of transitional SWBLIs are rare in the literature. Similarly, recent studies at hypersonic Mach numbers have considered the boundary-layer and shear-layer disturbances which are amplified within the separation region of transitional SWBLIs. They found that a disturbance was amplified in the shear layers of these interactions which was distinct from the disturbance which dominates the transition process in axisymmetric, hypersonic boundary layers, the second-mode instability. However, there are gaps in the literature between the amplification of shear-layer instabilities, their breakdown to turbulent spots within the interaction region, and the resulting effects on the flowfields of these SWBLIs. The present thesis aims to bridge these gaps by linking the measurement of shear-layer instabilities, observations of turbulent spot formation, and movement of the separation region. A technique was also developed and implemented experimentally to confirm the link between turbulent spot formation and SWBLI unsteadiness. This technique can be used in future numerical work to reproduce such results without needing computationally-expensive simulations of the shear-layer transition process.

Authors: Hembling, EP

• DOI: 10.5287/ora-xobog0v7m
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: hypersonics; boundary-layer transition; shock wave/boundary-layer interactions; aerodynamics
• Subjects: Aerodynamics, Hypersonic