On the influence of modelling choices on combustion in narrow channels

Kang, Xin; Gollan, Rowan; Jacobs, Peter A.; Veeraragavan, Ananthanarayanan

doi:10.1016/j.compfluid.2016.11.017

Cited by 32 publications

(15 citation statements)

References 55 publications

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“…For those variables displaying monotonic convergence, the recommendations of Stern at al. (2001) [29,30] were followed with the calculated grid convergence indices suggesting that the finest grid should match the Richardson extrapolated value of an infinitely refined grid to within 0.2%. For those displaying oscillatory convergence, the method in [29] requires an additional solution.…”

Section: Iiii 22 Computational Meshesmentioning

confidence: 99%

Performance of high mach number scramjets - Tunnel vs flight

et al. 2018

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While typically analysed through ground-based impulse facilities, scramjets experience significant heating loads in flight, raising engine wall temperatures and the fuel used to cool them beyond standard laboratory conditions. Hence, the present work numerically compares an access-to-space scramjet's performance at both these conditions. The Mach 12 Rectangular-to-Elliptical Shape-Transitioning scramjet flow path is examined via three-dimensional and chemically reacting Reynolds-averaged Navier-Stokes solutions. Flight operation is modelled through 800 K and 1800 K inlet and combustor walls respectively, while fuel is injected at both inlet-and combustor-based stations at 1000 K stagnation temperature. Room temperature walls and fuel plena model shock tunnel conditions. Mixing and combustion performance indicates that while flight conditions promote rapid mixing, high combustor temperatures inhibit the completion of reaction pathways, with reactant dissociation reducing chemical heat release by 16%. However, the heated walls in flight ensured 28% less energy was absorbed by the walls. While inlet fuel injection promotes robust burning of combustor-injected fuel, premature ignition upon the inlet in flight suggests these injectors should be moved further downstream. Coupled with counteracting differences in heat release and loss to the walls, the optimal engine design for flight may differ considerably from that which gives the best performance in the tunnel.

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Section: Iiii 22 Computational Meshesmentioning

confidence: 99%

Performance of high mach number scramjets - Tunnel vs flight

et al. 2018

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“…While displaying convergent behaviour, the variables were not universally monotonic. For those variables displaying monotonic convergence, the recommendations of Stern et al (2001) (employed by Kang et al (2017)) were followed with the calculated grid convergence indices suggesting that the finest grid should match the Richardson extrapolated value of an infinitely refined grid to within 0.2%. For those displaying oscillatory convergence, the method of Stern et al (2001) requires an additional solution.…”

Section: Computational Meshesmentioning

confidence: 99%

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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“…Additionally, results from the transient simulations allowed for the observation of oscillations in simulation parameters (temperature), at operating conditions close to flame extinction; these oscillations were used to identify the stability limits of combustor configurations considered. Finally, low wall thermal conductivity was observed to reduce the heat transfer in the post flame region, which in turn served to reduce the heat recirculation and preheating of the reactants in the pre-flame zone A computational investigation by Kang et al [8] From the results, it was concluded that 'auto-ignition' (the natural ignition of the reactants as a result of a sufficiently high ignition temperature) might not be possible, for cases considering CHT, due to the inability to generate the critical quantity of radicals necessary to sustain combustion. To counteract the failed ignition, during the investigation a pre-simulated flow with one tenth of the mass flow rate of the combustion simulation, the preheating served to allow for ignition utilising the auto-ignition method.…”

Section: Microcombustor Simulation and Modellingmentioning

confidence: 99%

“…The simulated model considered the domain depicted in Figure 13. Simulation parameters, detailed in Table 6, were selected in accordance with those presented in [8], serving to recreate variations on the work produced by Chambers [19], which would further verify the performance of the orthotropic module; as well as provide external data for comparison. It should also be noted that the simulations considered were run on a relatively coarse mesh, Lastly, the various configuration options for the simulation parameters were maintained for the comparison, with the configuration options selected reflective of the simulation domain and boundary conditions proposed in Figure 13, with the most notable being the use of the Euler time step method (which is 1 st order accurate in time); refer to Appendix A & B for the specific configuration options.…”

Section: Initial Microcombustor Simulation 61 Simulation Definitionmentioning

confidence: 99%

UQ eSpace

Vince¹

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The enclosed thesis details an investigation into the simulation of microcombustors with thermally orthotropic walls, using Eilmer4. The thesis details the motivational context for the work completed, then utilises this foundation to define the scope and aims of the project; the development of functional microcombustors simulations in Eilmer4. An initial review of relevant literature, predominantly relating to previous works in simulating microcombustion and heat recirculation. From the review of literature, a series of required simulation features allowing microcombustors with thermally orthotropic walls to be simulated in Eilmer4. These features and the varying degrees of implementation were documented and used to direct efforts towards a functioning microcombustor model with thermally orthotropic walls; the numerical approach required to allow various solid-fluid interfaces with the previously developed anisotropic sold module. Pending the implementation of the numerical schemes proposed two sets of simulations were completed. The first relating to simulating an insulated microcombustor for both the isotropic and thermally orthotropic considerations; serving to confirm the model. The second set of simulations considered the modelling of microcombustors with a high degree of thermal orthotropy, and the flame response in the presence of convective heat loss on the external combustor surface; with short term simulations achieving flame stability for the prescribed simulation conditions.

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On the influence of modelling choices on combustion in narrow channels

Cited by 32 publications

References 55 publications

Performance of high mach number scramjets - Tunnel vs flight

Performance of high mach number scramjets - Tunnel vs flight

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

UQ eSpace

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