2 results
Mechanism of detonation stabilization in a supersonic model combustor
- Xiaodong Cai, Ralf Deiterding, Jianhan Liang, Yasser Mahmoudi, Mingbo Sun
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- Journal:
- Journal of Fluid Mechanics / Volume 910 / 10 March 2021
- Published online by Cambridge University Press:
- 18 January 2021, A40
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The present work studies numerically the quasi-steady propagation of a hydrogen/oxygen detonation in a supersonic model combustor consisting of a cavity and an expanding wall. The two-dimensional reactive compressible Navier–Stokes equations with a one-step and two-species reaction model are solved using a hybrid sixth-order weighted essentially non-oscillatory-centred difference scheme combined with a structured adaptive mesh refinement technique. The results show that, after the shutdown of the hot jet, the detonation wave is successfully stabilized quasi-steadily in the supersonic model combustor together with periodic fluctuations of the detonation front. The formation of the quasi-steady propagation of detonation in the model combustor is mainly due to the combined effects of (i) pressure oscillations generated in the cavity, which facilitate the detonation propagation, and (ii) lateral mass divergence brought by the expanding wall, which can lead to detonation attenuation, and an unburned jet associated with large-scale vortices resulting from a Prandtl–Meyer expansion fan. This expansion fan is generated because of the expanding wall, which can contribute to the detonation stabilization. It is found that, for an incoming velocity lower than the Chapman–Jouguet value, a quasi-steady propagation of the detonation wave cannot be achieved. However, for incoming velocity higher than the Chapman–Jouguet value, a stabilization can be realized. This is effectively due to the formation of a periodic process, including four stages of forward propagation, detonation attenuation, backward propagation and detonation bifurcation, indicating the influence of the supersonic model combustor on the overall process.
Diffusion and mixing effects in hot jet initiation and propagation of hydrogen detonations
- Xiaodong Cai, Ralf Deiterding, Jianhan Liang, Mingbo Sun, Yasser Mahmoudi
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- Journal:
- Journal of Fluid Mechanics / Volume 836 / 10 February 2018
- Published online by Cambridge University Press:
- 11 December 2017, pp. 324-351
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In the present work, the role of diffusion and mixing in hot jet initiation and detonation propagation in a supersonic combustible hydrogen–oxygen mixture is investigated in a two-dimensional channel. A second-order accurate finite volume method solver combined with an adaptive mesh refinement method is deployed for both the reactive Euler and Navier–Stokes equations in combination with a one-step and two-species reaction model. The results show that the small-scale vortices resulting from the Kelvin–Helmholtz instability enhance the reactant consumption in the inviscid result through the mixing. However, the suppression of the growth of the Kelvin–Helmholtz instability and the subsequent formation of small-scale vortices imposed by the diffusion in the viscous case can result in the reduction of the mixing rate, hence slowing the consumption of the reactant. After full initiation in the whole channel, the mixing becomes insufficient to facilitate the reactant consumption. This applies to both the inviscid and viscous cases and is due to the absence of the unburned reactant far away from the detonation front. Nonetheless, the stronger diffusion effect in the Navier–Stokes results can contribute more significantly to the reactant consumption closely behind the detonation front. However, further downstream the mixing is expected to be stronger, which eventually results in a stronger viscous detonation than the corresponding inviscid one. At high grid resolutions it is vital to correctly consider physical viscosity to suppress intrinsic instabilities in the detonation front, which can also result in the generation of less triple points even with a larger overdrive degree. Numerical viscosity was minimized to such an extent that inviscid results remained intrinsically unstable while asymptotically converged results were only obtained when the Navier–Stokes model was applied, indicating that solving the reactive Navier–Stokes equations is expected to give more correct descriptions of detonations.