A combined cycle approach to dual-mode scramjet design and analysis

Lee, Gyu Sub S

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https://hdl.handle.net/2142/121483 Copy

Description

Title

A combined cycle approach to dual-mode scramjet design and analysis

Author(s)

Lee, Gyu Sub S

Issue Date

2023-07-11

Director of Research (if dissertation) or Advisor (if thesis)

Lee, Tonghun

Doctoral Committee Chair(s)

Lee, Tonghun

Committee Member(s)

• Elliott, Gregory S
• Dutton, J C
• Panerai, Francesco

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• scramjet
• ramjet
• hypersonic
• airbreathing
• dual-mode
• supersonic combustion, propulsion

Abstract

Hypersonic flight has been established as a key aeronautical capability for the next generation of human air and spacefaring ventures. Instrumental to the development of practical hypersonic aircraft and associated technologies is the maturation of the supersonic combustion ramjet (scramjet) engine. This hypersonic airbreathing powerplant, which is fundamentally comprised of a high-speed flowpath with no moving parts, belies its structural simplicity with the attendance of incredibly rich fluid and flame dynamics that govern its design and operation. While great strides have been made towards characterizing the important physical processes in these flows, they elude adequate modeling due to the complexities and coupling of the phenomena present and the difficulty in reproducing relevant flows in current ground test facilities. Flight testing is a crucial phase in the comprehensive study of hypersonic and scramjet-related flows. To glean fundamental insight into these flows from these high-cost experiments it is important to ground the design of a scramjet test article in sensible and tractable fluid dynamics. The first part of the current work establishes a generalized methodology for an inlet-to-nozzle design of a scramjet flowpath with an emphasis on derivation from gasdynamics first principles and simplified parametric studies, including a novel relation for the divergence required for an ideal supersonic combustor and the effect of injection port sizing and fuel scheduling on the penetration and spread of fuel in the combustor. The resulting set of formulations and models were incorporated into a suite of scramjet design tools which were implemented in the design of a benchmark Mach 7 dual-mode scramjet flowpath. This design process was conducted in parallel with and informed by high-fidelity simulations of the full flowpath. An experimental characterization of the axisymmetric isolator-combustor geometry for the newly developed flowpath was conducted as a direct-connect configuration in the ACT-II arc-heated hypersonic wind tunnel. It was revealed that at the ground test conditions the current geometry struggled to achieve the expected combustion performance. A prototype flowpath with a revised cavity geometry and simplified, constant-area combustor geometry was tested, yielding a far more robust combustion performance. From these results, the rapid expansion of the original flowpath at the flameholding station of the combustor and resulting decrease in pressure was identified as the primary source of loss of performance. Flow choking studies were performed in both axisymmetric and rectangular scramjet flowpaths, revealing notable differences in the shock train structure and the dynamics of the advancing pseudoshock during mode transition and choking phases. Lastly, the original direct-connect flowpath was utilized in a successful demonstration of a rocket-based combined cycle (RBCC) combustion mode transition. In the final portion of the current work, original analyses of the thermodynamics and gasdynamics that govern the theoretical performance of dual-mode scramjets are conducted. The accompanying discussion of the analytical process and findings, supplemented by experimental observations, seeks to address common uncertainties and misconceptions regarding the dominant fluid processes present in these engines. Some topics covered include the differences in performance between scram and ram combustion modes, the impetus and consequence of choking and inlet unstart, and the thrust and fuel efficiencies of an ideal scramjet at various flight conditions and their departure from classical Brayton cycle predictions. This theoretical overview is meant to provide an intuitive technical perspective on supersonic combustion and dual-mode scramjet operation that may be helpful to aerospace students and researchers in the field alike.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

© 2023 by Gyu Sub Lee. All rights reserved.

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