Doctoral Dissertations

Date of Award

8-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

Trevor M. Moeller

Committee Members

Phil A. Kreth, Ryan B. Bond, Kevin R. Holst, Sarah E. Armstrong

Abstract

The complexity of a scramjet isolator flowfield is magnified by the presence of wall-bounded intersecting no-slip walls that introduce secondary flows, vortical structures, and turbulent boundary layers interacting with the shock structure of the primary flowfield. Experimental studies have shown that the onset and magnitude of corner flow separation can have a significant impact on primary centerline separation in the presence of strong Shock Boundary Layer Interactions (SBLI). A computational study of the three-dimensional characteristics of a scramjet isolator flow path is conducted to gain an understanding of how viscous corner interactions influence the formation and stability of the isolator shock train. This work leverages a multi-fidelity computational fluid dynamics (CFD) campaign with an experimental study to identify the underlying physics introduced by the viscous corner region affecting the primary flowfield. A cylindrical rod was inserted into the flow downstream of the isolator to simulate pressure rises associated with combustion-induced effects that can lead to upstream shock propagation, premature mode transition, and potential unstart. This enables the experimental facility to fine-tune the onset and position of the pre-combustion shock train (PCST) and track the conditions that can lead to the detection of the unstart process. The experimental data are collected via static pressure probes, Kulite pressure probes, and Background Oriented Schlieren (BOS) imaging to give a quantitative and qualitative analysis of the flowfield. This CFD study employs an Improved Delayed Detached Eddy Simulation (IDDES) to capture the flow mechanisms that drive the formation and upstream propagation of the pre-combustion shock train (PCST) within the scramjet isolator. The mechanisms and flow physics investigated include downstream flow blockage, shock train behavior, and viscous corner interactions with the shock train. Focus is placed on the viscous corner regions, where three-dimensional secondary flows are tracked throughout the extent of the shock train. These corner interactions are analyzed to characterize and assess their influence on the unsteady behavior of the shock system. The magnitude and structure of the corner vortices are found to vary in response to the shock train position, where correlations are identified between vortex evolution and shock train unsteadiness.

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