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Flame propagation along the vortex axis
Umeå University, Faculty of Science and Technology, Physics.
Umeå University, Faculty of Science and Technology, Physics.
2006 (English)In: Combustion theory and modelling, ISSN 1364-7830, Vol. 10, no 4, 581-601 p.Article in journal (Refereed) Published
Abstract [en]

The problem of how to include fast burning along the vortex axis into the general description of turbulent flames is discussed. It is shown that, from such a point of view, the most representative geometry of the flow is burning in a hypothetic 'tube' with rotating gaseous mixture. Direct numerical simulations of flame propagation in the hypothetic tube are performed on the basis of the complete system of hydrodynamic equations, including thermal conduction, diffusion, viscosity and chemical kinetics written in the rotational reference frame. The geometry of an axisymmetric flame front is studied, which allows reducing the dimension of the problem by one, thus saving computational time. The numerical results are analysed using the ideas of bubble rising in the acceleration field created by the centrifugal force. It is shown that the velocity of flame propagation is determined mostly by the velocity of bubble rising when the frequency of the tube rotation is sufficiently large. When the rotational frequency is moderate, then the velocity of flame propagation is determined by the planar flame velocity, by the hydrodynamic flame instability and by the gas rotation. Calculations given in the present paper are in agreement with the previous theoretical and experimental results.

Place, publisher, year, edition, pages
2006. Vol. 10, no 4, 581-601 p.
Keyword [en]
Premixed flame, Turbulent vortex, Hydrodynamic instability, Bubble rising
URN: urn:nbn:se:umu:diva-2477DOI: 10.1080/13647830600552006OAI: diva2:140620
Available from: 2007-08-28 Created: 2007-08-28Bibliographically approved
In thesis
1. Numerical study of flame dynamics
Open this publication in new window or tab >>Numerical study of flame dynamics
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Modern industrial society is based on combustion with ever increasing standards on the efficiency of burning. One of the main combustion characteristics is the burning rate, which is influenced by intrinsic flame instabilities, external turbulence and flame interaction with walls of combustor and sound waves.

In the present work we started with the problem how to include combustion along the vortex axis into the general theory of turbulent burning. We demonstrated that the most representative geometry for such problem is a hypothetic “tube” with rotating gaseous mixture. We obtained that burning in a vortex is similar to the bubble motion in an effective acceleration field created by the centrifugal force. If the intensity of the vortex is rather high then the flame speed is determined mostly by the velocity of the bubble. The results obtained complement the renormalization theory of turbulent burning. Using the results on flame propagation along a vortex we calculated the turbulent flame velocity, compared it to the experiments and found rather good agreement.

All experiments on turbulent combustion in tubes inevitably involve flame interaction with walls. In the present thesis flame propagation in the geometry of a tube with nonslip walls has been widely studied numerically and analytically. We obtained that in the case of an open tube flame interaction with nonslip walls leads to the oscillating regime of burning. The oscillations are accompanied by variations of the curved flame shape and the velocity of flame propagation. If flame propagates from the closed tube end, then the flame front accelerates with no limit until the detonation is triggered. The above results make a good advance in solving one of the most difficult problems of combustion theory, the problem of deflagration to detonation transition. We developed the analytical theory of accelerating flames and found good agreement with results of direct numerical simulations. Also we performed analytical and numerical studies of another mechanism of flame acceleration caused by initial conditions. The flame ignited at the axis of a tube acquires a “finger” shape and accelerates. Still, such acceleration takes place for a rather short time until the flame reaches the tube wall. In the case of flame propagating from the open tube end to the closed one the flame front oscillates and therefore generates acoustic waves. The acoustic waves reflected from the closed end distort the flame surface. When the frequency of acoustic mode between the flame front and the tube end comes in resonance with intrinsic flame oscillations the burning rate increases considerably and the flame front becomes violently corrugated.

Place, publisher, year, edition, pages
Umeå: Fysik, 2007. 73 p.
combustion, Direct Numerical Simulation (DNS), turbulence, flame-vortex interaction, flame acceleration, flame-acoustic interaction
National Category
Physical Sciences
urn:nbn:se:umu:diva-1313 (URN)978-91-7264-351-2 (ISBN)
Public defence
2007-09-21, KB3A9, KBC-huset, SE-901 87, Umeå University, Sweden, Umeå, 13:00 (English)
Available from: 2007-08-28 Created: 2007-08-28 Last updated: 2009-08-19Bibliographically approved

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