Doctoral Dissertations

Orcid ID

0000-0001-5479-1328

Date of Award

8-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

Phillip A. Kreth

Committee Members

John D. Schmisseur, Mark T. Gragston, Trevor M. Moeller, Ryan S. Glasby

Abstract

Shockwave / boundary-layer interactions (SBLI) are a prevalent, high-risk fluid phenomena on supersonic and hypersonic aircraft that have significant implications for a vehicle's overall flight performance and safety. Their unsteady nature can generate large gradients in shear layer properties and localized thermal loads, and due to their complexity. With the use of newly developed diagnostic capabilities and analysis methods, it is possible to begin a systematic and efficient study of the driving behavior in transitional and turbulent shockwave / boundary-layer interactions. This investigation aimed to quantitatively measure characteristic SBLI features, capture general SBLI dynamics as a product of the incoming boundary layer state, understand how frequency content associated with characteristic SBLI unsteadiness changes during the transition process, and assess what driving mechanisms promote the growth and collapse of the separation bubble.

To complete this assessment a cylindrical shock generator was installed on a 6-degree axisymmetric cone to study both transitional and turbulent shockwave / boundary-layer interactions in the UTSI Mach 4 Ludwieg tube. High-speed schlieren imaging and pressure-sensitive paint were utilized. Data analysis included power spectral densities, spectral heat maps, POD, DMD, a custom feature-tracking algorithm, and analysis between the separation shock, upstream influence, and a distinct boundary-layer thickening feature.

The high-speed schlieren imaging time series images display a shock collapse from an upstream disturbance in the incoming boundary layer. The upstream influence is seen to bow in response to the turbulent packet as it is pushed downstream. Following this collapse, the upstream influence appears to have a linear restoring behavior upstream towards its originating position. Local frequency probes generally see the most prominent frequencies at the mean location of these ranges of influence. As the SBLI shock generator is moved downstream, this frequency peak shifts to a higher frequency and is suspected to scale with the incoming boundary layer height. The dominant modes in the POD analysis revealed a shift in the SBLI structure between the first two and the final two-cylinder shock generator locations. In the DMD analysis, modes associated with rapid growth mechanisms were identified. A relationship between the UI presence and boundary layer thickening behavior was observed.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS