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DNS analysis of boundary layer flashback in turbulent flow with wall-normal pressure gradient

DNS analysis of boundary layer flashback in turbulent flow with wall-normal pressure gradient
DNS analysis of boundary layer flashback in turbulent flow with wall-normal pressure gradient
The presence of swirl in combustion systems produces a marked change in their boundary layer flashback behaviour. Two aspects of swirling flow are investigated in this study: the effect of the swirl-generated wall-normal pressure gradient, and the effect of misalignment between the mean flow direction and the direction of flame propagation. The analysis employs Direct Numerical Simulation (DNS) of fuel-lean premixed hydrogen-air flames in turbulent planar channel flow with friction Reynolds number of 180. The effect of swirl on the flashback process is investigated by imposing a wall-normal pressure gradient profile. Analysis of the DNS data shows how the resulting differences in flow field and flame topology contribute to the differences in the overall flashback speed. Misalignment of the flow and propagation directions leads to asymmetry in the flame shape statistics as streaks of high velocity fluid in the boundary layer cleave into the flame front at an angle, yielding an increase in flame surface density away from the wall. Swirl has a stabilising effect on the turbulent flame front during flashback along the centre-body of a swirling annular flow due to the density stratification across the flame front, and produces a reduction in turbulent consumption speed. However the swirl also sets up a hydrostatic pressure difference that drives the flame forward, and the net effect is that the flashback speed is increased. The dominance of hydrostatic effects motivates development of relatively simple modelling for the effect of swirl on flashback speed. A model accounting for the inviscid momentum balance and for confinement effects is presented which adequately describes the effect of swirl on flashback speed observed in previous experimental studies.

turbulent channel flow, turbulent premixed flames, boundary-layer flashback, swirl flames, flashback-limit model
1540-7489
2791-2799
Bailey, James Richard
4ce63026-939f-4d32-90cb-24ac23580fbf
Richardson, Edward
a8357516-e871-40d8-8a53-de7847aa2d08
Bailey, James Richard
4ce63026-939f-4d32-90cb-24ac23580fbf
Richardson, Edward
a8357516-e871-40d8-8a53-de7847aa2d08

Bailey, James Richard and Richardson, Edward (2020) DNS analysis of boundary layer flashback in turbulent flow with wall-normal pressure gradient. Proceedings of the Combustion Institute, 38 (2), 2791-2799. (doi:10.1016/j.proci.2020.06.004).

Record type: Article

Abstract

The presence of swirl in combustion systems produces a marked change in their boundary layer flashback behaviour. Two aspects of swirling flow are investigated in this study: the effect of the swirl-generated wall-normal pressure gradient, and the effect of misalignment between the mean flow direction and the direction of flame propagation. The analysis employs Direct Numerical Simulation (DNS) of fuel-lean premixed hydrogen-air flames in turbulent planar channel flow with friction Reynolds number of 180. The effect of swirl on the flashback process is investigated by imposing a wall-normal pressure gradient profile. Analysis of the DNS data shows how the resulting differences in flow field and flame topology contribute to the differences in the overall flashback speed. Misalignment of the flow and propagation directions leads to asymmetry in the flame shape statistics as streaks of high velocity fluid in the boundary layer cleave into the flame front at an angle, yielding an increase in flame surface density away from the wall. Swirl has a stabilising effect on the turbulent flame front during flashback along the centre-body of a swirling annular flow due to the density stratification across the flame front, and produces a reduction in turbulent consumption speed. However the swirl also sets up a hydrostatic pressure difference that drives the flame forward, and the net effect is that the flashback speed is increased. The dominance of hydrostatic effects motivates development of relatively simple modelling for the effect of swirl on flashback speed. A model accounting for the inviscid momentum balance and for confinement effects is presented which adequately describes the effect of swirl on flashback speed observed in previous experimental studies.

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PROCI_TurbFlash1 - Accepted Manuscript
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Accepted/In Press date: 8 June 2020
e-pub ahead of print date: 28 July 2020
Keywords: turbulent channel flow, turbulent premixed flames, boundary-layer flashback, swirl flames, flashback-limit model

Identifiers

Local EPrints ID: 442062
URI: http://eprints.soton.ac.uk/id/eprint/442062
ISSN: 1540-7489
PURE UUID: 6d168d24-3936-4891-b826-9bc61c28208f
ORCID for James Richard Bailey: ORCID iD orcid.org/0000-0002-8784-4008
ORCID for Edward Richardson: ORCID iD orcid.org/0000-0002-7631-0377

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Date deposited: 06 Jul 2020 16:31
Last modified: 28 Apr 2022 05:14

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Author: James Richard Bailey ORCID iD

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