Computational Investigation of Thermal Nonequilibrium Effects in Scramjet Geometries

Gehre, Rolf; Wheatley, Vincent; Boyce, Russell

doi:10.2514/1.b34722

Cited by 11 publications

(5 citation statements)

References 21 publications

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“…Gradients of viscous fluxes are calculated through weighted least-squares fits, with Blottner curve fits used to model viscosity. Solutions are generated using the data-parallel line relaxation method [27], an implicit time marching scheme [28].…”

Section: A Numerical Solvermentioning

confidence: 99%

Characteristics of Cascaded Fuel Injectors Within an Accelerating Scramjet Combustor

2016

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Performances of cascaded hydrogen injectors within an accelerating scramjet combustor were characterized via a three-dimensional numerical study. Two streamwise-aligned jets are employed, with the upstream injector half the diameter of the rear jet. Each are inclined at 45 deg to the freestream and achieve a jet-to-freestream momentum ratio of unity. Performance was evaluated over a range of freestream Mach numbers, modeling combustor entrance conditions on an accelerating access-to-space scramjet trajectory. Distance between injectors was varied to estimate the optimum jet-to-jet spacing to achieve robust performance across the Mach number range. It is shown that the downstream injector benefits jointly from shielding effects induced by the smaller upstream injector, as well as its increased diameter. Injector spacings greater than two total jet diameters D t displayed improved absolute jet penetration, spanwise spread, and entrainment rates over an equivalent single injector across all Mach numbers. Jet bow shock pressure recovery was improved at spacings above 4D t . Unique optimal injector spacings existed for each performance metric, at each freestream Mach number examined. Although no universal optimum spacing was determined, spacings between 4 and 6D t provided substantial performance enhancements over single injectors, throughout the accelerating scramjet flight conditions.

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Section: A Numerical Solvermentioning

confidence: 99%

Characteristics of Cascaded Fuel Injectors Within an Accelerating Scramjet Combustor

2016

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“…The eighth chapter; in which thermal non-equilibrium effects on flow structures and combustion features are discussed for two-and three-dimensional scramjet simulations using RANS. The two-dimensional investigation has been published in [68].…”

Section: Discussionmentioning

confidence: 99%

The flow physics of inlet-fueled, low-compression scramjets

Gehre¹

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“…Gradients of viscous fluxes are calculated through weighted least-squares fits, with Blottner curve fits used to model viscosity. Solutions are generated using the Data-Parallel Point Relaxation method (Wright et al, 1998), an implicit time marching scheme (Gehre et al, 2013).…”

Section: Numerical Solvermentioning

confidence: 99%

“…Gradients of viscous fluxes are calculated through weighted least-squares fits, with Blottner curve fits used to model viscosity. Solutions are marched to convergence using the implicit Euler scheme, making use of the point relaxation method (Wright et al, 1998;Gehre et al, 2013). The RANS approach utilised is capable of capturing primary flow features, while US3D has been successfully validated against experimental data in prior works (Barth et al, 2015a;Barth et al, 2015b).…”

Section: Engine Flow Path and Numerical Techniquesmentioning

confidence: 99%

“…Species-specific viscosity is determined through Blottner curve fits (Blottner et al, 1971). Solutions are generated using the implicit time marching Data-Parallel Point Relaxation method (Wright et al, 1998;Gehre et al, 2013). Turbulence was evaluated using the one equation, Spalart and Allmaras (1992) model, with initial turbulent viscosity set to be 3% of the Sutherland viscosity, default in US3D.…”

Section: Numerical Solvermentioning

confidence: 99%

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Improving performance of high Mach number scramjets: fuelling strategies and combustor design

Landsberg¹

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With prospective flight speeds exceeding Mach 12, airbreathing scramjets, incorporated in hybrid satellite launch vehicles, offer efficiency and operability benefits when compared to rocket-based systems. By capturing atmospheric air, the scramjet second stage negates the requirement for onboard oxidisers. Addressing the small satellite niche market, these hybrid systems provide a cost-effective solution to launching such payloads to orbit. At hypersonic speeds, however, conventional wing-mounted engine nacelles are not viable; the scramjet must be integrated to the airframe. Hence, the flight-candidate, Mach 12 Rectangular-to-Elliptical Shape-Transitioning (M12REST) scramjet blends a rectangular capture area (permitting parallel mounting of engine modules to the planar vehicle underside), with a structurally efficient elliptical combustor. As access-to-space scramjets suffer immense heating loads, and engine airflow residence times approach air-fuel reaction timescales, hydrogen fuel is utilised for its exceptional cooling capacity and rapid ignition characteristics. However, efficient fuelling techniques are required to avoid crippling the engine's performance through conservative combustor lengths. This thesis numerically and experimentally investigated whether the performance of such an airframe-integrated scramjet can be sufficiently enhanced through customisation of fuel injection and combustor geometry to achieve net thrust at Mach 12. Three-dimensional, chemically reacting Reynolds-averaged Navier-Stokes solutions enabled numerical analysis, while experimental validation was performed within The University of Queensland's, T4 Stalker Tube.Preliminary work investigated cascaded fuel injectors, targeting mixing and penetration improvements. Two streamwise-aligned jets were employed, with the upstream injector half the diameter of the rear, while the distance between each was varied. The upstream jet induced a low dynamic pressure region in its wake, shielding the downstream jet from the hypersonic crossflow. The leeward jet benefits from an increased local jet-to-freestream momentum ratio, while its larger diameter increases absolute penetration. Examining performance at M12REST mean combustor entrance conditions, unique optimal injector spacings existed for each performance metric, displaying improved penetration, spread, and mixing across the range of flight Mach numbers examined (6 ≤ M ≤ 12). However, jet-to-jet spacings of 4-6 total jet diameters displayed universal performance enhancements over single fuel jets. With penetration improvements of 30-40%, and mixing improvements of 40-70%, the simple fixed geometry, passive technique is ideal for use within an accelerating access-to-space scramjet.While cascaded injectors improved performance within uniform flows, the flows ingested by airframe-integrated scramjets are far less homogeneous. Non-uniform compression fields combine with thick boundary layers developed over the vehicle forebody to deliver density stratified flow to the combustor. This thesis ...

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Computational Investigation of Thermal Nonequilibrium Effects in Scramjet Geometries

Cited by 11 publications

References 21 publications

Characteristics of Cascaded Fuel Injectors Within an Accelerating Scramjet Combustor

Characteristics of Cascaded Fuel Injectors Within an Accelerating Scramjet Combustor

The flow physics of inlet-fueled, low-compression scramjets

Improving performance of high Mach number scramjets: fuelling strategies and combustor design

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