1,720,995 research outputs found
Large Eddy simulation of turbulent hydrogen-fuelled supersonic combustion in an air cross-flow
No full textThe main aim of this article is to provide a theoretical understanding of the physics of supersonic mixing and combustion. Research in advanced air-breathing propulsion systems able to push vehicles well beyond is of interest around the world. In a scramjet, the air stream flow captured by the inlet is decelerated but still maintains supersonic conditions. As the residence time is very short , the study of an efficient mixing and combustion is a key issue in the ongoing research on compressible flows. Due to experimental difficulties in measuring complex high-speed unsteady flowfields, the most convenient way to understand unsteady features of supersonic mixing and combustion is to use computational fluid dynamics. This work investigates supersonic combustion physics in the Hyshot II combustion chamber within the Large Eddy simulation framework. The resolution of this turbulent compressible reacting flow requires: (1) highly accurate non-dissipative numerical schemes to properly simulate strong gradients near shock waves and turbulent structures away from these discontinuities; (2) proper modelling of the small subgrid scales for supersonic combustion, including effects from compressibility on mixing and combustion; (3) highly detailed kinetic mechanisms (the Warnatz scheme including 9 species and 38 reactions is adopted) accounting for the formation and recombination of radicals to properly predict flame anchoring. Numerical results reveal the complex topology of the flow under investigation. The importance of baroclinic and dilatational effects on mixing and flame anchoring is evidenced. Moreover, their effects on turbulence-scale generation and the scaling law are analysed
A review on hydrogen industrial aerospace applications
No full textThis article depicts the scenario in which hydrogen appears as the best candidate fuel for long range transportation with potentially zero emissions. Main characteristics of hydrogen that make it appealing and exploitable in applications are described and compared to those of other common fuels. A historical journey through aerospace industry applications of hydrogen since its discovery is provided, considering turbojet, ramjet, scramjet and rocket engines. Current and future technology levels are reported. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
COMPARISON OF SIZE DISTRIBUTION FROM VARIOUS PARTICLE SIZING TECHNIQUES IN THE NANOMETER SIZE RANGE
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Non premixed Supersonic flames: Combustion models
No full textThe aim of this work is to investigate the validity of combustion models that were developed for low-speed combustion and then traditionally extended to high-speed combustion. In fact, the assumption of fast chemistry, as well as the flamelet chemistry model, must be validated in supersonic flows, where compressibility may affect the flame structure. LES of the HyShot test case, showed that the interactions between the airstream entering the combustor and the H2 sonic jet produce an average vorticity of order 105 Hz. The interaction between the hydrogen transverse jets and the supersonic air flow leads to bow shock formation and, accordingly, to boundary layer separation. This separation allows H2 to be convected upstream through the spanwise recirculation vortices created by the baroclinic effect. Once created, the vortices are tilted, stretched, compressed and expanded according to the vorticity transport equation. These vortices are the key structures responsible for the observed fast fuel air mixing. In this context, an analysis of the flame structure is of theoretical and numerical interest. In fact, depending on this structure, a appropriate kinetic and chemical/turbulence model can be chosen to correctly predict experimental results. The flame structure has been analyzed by means of the Burke and Schumann theory
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