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Diffusion and mixing effects in hot jet initiation and propagation of hydrogen detonations

Diffusion and mixing effects in hot jet initiation and propagation of hydrogen detonations
Diffusion and mixing effects in hot jet initiation and propagation of hydrogen detonations
In the present work, the role of the diffusion and mixing in hot jet initiation and detonation propagation in a supersonic 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. Rather than the well-known classification of weakly unstable and highly unstable detonations when considering viscous simulations, it should be more correct to clarify whether the unburned reactant can be fully consumed behind the shock front. Further, 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.
0022-1120
324-351
Cai, Xiaodong
293bf621-f0e1-48ba-abaa-b41da81ea244
Deiterding, Ralf
ce02244b-6651-47e3-8325-2c0a0c9c6314
Liang, Jianhan
fd8229b7-c7f4-4a1b-b94f-abce393f9e9a
Sun, Mingbo
2df9eb75-e5d8-48cf-b8e1-00b0b77b3a90
Mahmoudi, Yasser
5c336547-605b-4f01-afea-2fc24a922798
Cai, Xiaodong
293bf621-f0e1-48ba-abaa-b41da81ea244
Deiterding, Ralf
ce02244b-6651-47e3-8325-2c0a0c9c6314
Liang, Jianhan
fd8229b7-c7f4-4a1b-b94f-abce393f9e9a
Sun, Mingbo
2df9eb75-e5d8-48cf-b8e1-00b0b77b3a90
Mahmoudi, Yasser
5c336547-605b-4f01-afea-2fc24a922798

Cai, Xiaodong, Deiterding, Ralf, Liang, Jianhan, Sun, Mingbo and Mahmoudi, Yasser (2018) Diffusion and mixing effects in hot jet initiation and propagation of hydrogen detonations. Journal of Fluid Mechanics, 836, 324-351. (doi:10.1017/jfm.2017.770).

Record type: Article

Abstract

In the present work, the role of the diffusion and mixing in hot jet initiation and detonation propagation in a supersonic 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. Rather than the well-known classification of weakly unstable and highly unstable detonations when considering viscous simulations, it should be more correct to clarify whether the unburned reactant can be fully consumed behind the shock front. Further, 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.

Text MS_JFM - Accepted Manuscript
Restricted to Repository staff only until 11 May 2018.
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Text MS-JFM
Restricted to Repository staff only
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More information

Accepted/In Press date: 11 October 2017
e-pub ahead of print date: 11 December 2017
Published date: 10 February 2018

Identifiers

Local EPrints ID: 415034
URI: https://eprints.soton.ac.uk/id/eprint/415034
ISSN: 0022-1120
PURE UUID: a94ad277-50ca-42ea-8dfc-ecce32ff0a89
ORCID for Ralf Deiterding: ORCID iD orcid.org/0000-0003-4776-8183

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Date deposited: 23 Oct 2017 16:30
Last modified: 10 Feb 2018 17:30

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Contributors

Author: Xiaodong Cai
Author: Ralf Deiterding ORCID iD
Author: Jianhan Liang
Author: Mingbo Sun
Author: Yasser Mahmoudi

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