Supersonic combustion of hydrocarbon fuels in a three-dimensional Mach 8 scramjet

Denman, Zachary

doi:10.14264/uql.2018.8

Cited by 4 publications

(7 citation statements)

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“…To help alleviate this, two separate solenoids are utilised in the present work, each fed by independent LTs. This approach was successfully implemented by Denman (2017) to reduce the likelihood of observing 'false-positives' of hydrocarbon combustion during low enthalpy shots, while also providing greater control in plenum pressures. A schematic of the system as installed for the present work is given in Fig.…”

Section: Fuelling Geometries and Delivery Systemmentioning

confidence: 99%

“…While scramjet engines display improving technological readiness, financial constraints limit many researchers to ground-based impulse wind tunnels Denman et al (2016;2017), or numerical studies (Landsberg et al, 2018a). As Mach number increases, however, increased working pressures drive up the operational costs of reflected shock tunnels, while turbulent mixing between the driver and test gas interface reduces available test time .…”

Section: Introductionmentioning

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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Section: Fuelling Geometries and Delivery Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Landsberg¹

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“…It is stressed, however, that despite the grid being made up of structured elements, the underlying flow and adjoint solvers operate on the grid using numerical routines developed for unstructured grids. This methodology is common in computational analyses of complex hypersonic flows [215,216]. This work focussed on an unstructured grid implementation because we are optimistic that unstructured methods will mature in the near future to the point where residual convergence is no longer an issue.…”

Section: Selection Of Grid Topologymentioning

confidence: 99%

Adjoint-based aerodynamic design optimisation in hypersonic flow

Damm¹

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The drive for improved flexibility and reusability in satellite launch systems has brought a resurgence in the popularity of scramjet-powered access-to-space launch vehicle concepts. A challenge in scramjet-powered accelerator vehicles is achieving positive thrust margins at the high-speed end of their flight envelopes. As a consequence, scramjet-powered vehicles typically rely on highly integrated airframe-engine configurations. However, due to the tight integration, the geometries and the flow physics are complex. An automated optimisation method seems an excellent candidate approach to explore the complex design space of hypersonic vehicles. This thesis focuses on the development and application of a particular optimisation method, adjoint-based optimisation, to aid in efficient aerodynamic design in hypersonic flows. Shape optimisation of scramjet-powered vehicles requires many design parameters to capture the geometric detail, and, since the flow physics is complex, the fidelity of Reynolds-Averaged Navier-Stokes (RANS) analyses is desirable. The combination of many design parameters and an expensive objective function evaluation drives the need for gradient evaluation methods that scale well with the number of design variables. An advantage of the adjoint method is that all shape sensitivities for an objective function are evaluated at the cost of only one flow solution and one adjoint solution. As a result of its efficiency, the adjoint method has become widely used for aircraft design, evolving to the design optimisation of full configurations. Despite the wide use of adjoint methods in aircraft optimisation, there has been very little application to hypersonic vehicle design. Several high-speed adjoint solvers have been reported in the literature, however, a majority of these works have only verified the adjoint sensitivities, few have followed on to demonstrate the method for use in design optimisation. The contribution of this work is the description and application of a discrete adjoint solver in high-speed compressible flow optimisation. What is unique in this work is a demonstration that complex-step differentiation works well to linearise a second-order spatially accurate unstructured RANS solver. In particular, the approach presented in this work utilises the k − ω turbulence model in high-speed ducted flow configurations. As part of this work, to provide flow analysis with a rapid turnaround , an unstructured steadystate RANS solver driven by a Jacobian-Free Newton-Krylov method was developed. Turbulence is modelled using the two-equation k − ω turbulence model. The Newton method is globalised by using the pseudo-transient approach. A restarted GMRES method is used to solve the system of linear equations arising when solving for the Newton steps. Evaluation of the matrix-vector products required in the GMRES algorithm is accomplished by Fréchet derivatives using imaginary perturbations in the complex plane. This is necessary to achieve robust convergence of the types of turbulent hypersonic flows...

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“…As a consequence, the use of hydrocarbon fuels for scramjet powered vehicles is linked to the development of new injection, mixing and ignition systems that can enhance the combustion efficiencies over the scramjet's short residence times. Denman [57] showed supersonic combustion of hydrocarbon fuels in a Mach 7 scramjet engine, with a cavity flame-holder.…”

Section: Scramjet Processes and Characteristicsmentioning

confidence: 99%

Free-jet testing of a Mach 12 scramjet in an expansion tube

Toniato¹

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Scramjet technology has the theoretical potential to provide air-breathing propulsion as a more efficient alternative to conventional rocket propulsion. Since the vehicle captures its oxidiser from the atmosphere -as opposed to carrying it like a rocket -the specific impulse can theoretically be increased by an order of magnitude, thereby increasing payload mass fractions. In this context, threestage hybrid rocket-scramjet-rocket launch systems have shown to potentially provide a cost-effective and flexible solution for satisfying the requirements of the small-satellites market. However, to be economically feasible, the proposed scramjet-powered second stage would be reusable.Rectangular-to-Elliptical-Shape-Transitioning (REST) engines have shown to be a viable concept that can be integrated into access-to-space vehicles operating between Mach 5 and 12. The half-scale Mach 12 REST engine is a research scramjet specifically designed to operate in the last part of the ascent trajectory. Previous studies have demonstrated the ability of this design to successfully operate at equivalent flight conditions of Mach 11.6, 30 kPa dynamic pressure. However, tests have never been performed in freejet mode at the design conditions, as the facility which was used -the T4 reflected shock tunnel -was limited, like all RSTs by the extreme total pressure requirements of a Mach 12 flight. These limitations are aggravated by the even higher pressure necessary for pressure-length scaling, used to conserve the flow similarity between the half-scale experimental model and the flight engine.To overcome these limitations and allow freejet testing with pressure-length scaling, the use of expansion tubes has been proposed. These are currently the only kind of facility capable of producing these high-pressure requirements. Currently, the University of Queensland operates the X3 expansion tube, which is one of the few facilities worldwide with the potential to produce both the required total pressures and sufficiently long test times (up to 1.5 ms) to test an engine such as the Mach 12 REST engine.

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Supersonic combustion of hydrocarbon fuels in a three-dimensional Mach 8 scramjet

Cited by 4 publications

References 0 publications

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

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

Adjoint-based aerodynamic design optimisation in hypersonic flow

Free-jet testing of a Mach 12 scramjet in an expansion tube

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