TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Analysis of Combustion Induced Vortex Breakdown Driven Flame Flashback in a Premix Burner With Cylindrical Mixing Zone

[+] Author and Article Information
F. Kiesewetter, T. Sattelmayer

Lehrstuhl für Thermodynamik, Technische Unversität München, D-85748 Garching, Germany

M. Konle1

Lehrstuhl für Thermodynamik, Technische Unversität München, D-85748 Garching, Germanykonle@td.mw.tum.de


Corresponding author.

J. Eng. Gas Turbines Power 129(4), 929-936 (Apr 03, 2007) (8 pages) doi:10.1115/1.2747259 History: Received June 07, 2006; Revised April 03, 2007

In earlier experimental studies of the authors a previously unknown mechanism leading to flame flashback—combustion induced vortex breakdown (CIVB)—was discovered in premixed swirl burners. It exhibits the sudden formation of a recirculation bubble in vortical flows, which propagates upstream into the mixing zone after the equivalence ratio has exceeded a critical value. This bubble then stabilizes the chemical reaction and causes overheat with subsequent damage to the combustion system. Although it was shown earlier that the sudden change of the macroscopic character of the vortex flow leading to flashback can be qualitatively computed with three-dimensional as well as axisymmetric two-dimensional URANS-codes, the proper prediction of the flashback limits could not be achieved with this approach. For the first time, the paper shows quantitative predictions using a modified code with a combustion model, which covers the interaction of chemistry with vortex dynamics properly. Since the root cause for the macroscopic breakdown of the flow could not be explained on the basis of experiments or CFD results in the past, the vorticity transport equation is employed in the paper for the analysis of the source terms of the azimuthal component using the data delivered by the URANS-model. The analysis reveals that CIVB is initiated by the baroclinic torque in the flame and it is shown that CIVB is essentially a two-dimensional effect. As the most critical zone, the upstream part of the bubble was identified. The location and distribution of the heat release in this zone governs whether or not a flow field is prone to CIVB.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Experimental setup employed for the CIVB studies

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Figure 2

Flame position during sudden vortex breakdown in the tubular burner section (from high speed films recorded with a UV-intensified camera)

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Figure 3

Numerical simulation of a flashback occurring by the increase of Φ=0.83 to Φ=0.91

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Figure 4

Comparison of numerical results obtained with the full 3D model and the axisymmetric 2D model

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Figure 5

Model sensitivity regarding the annular gap mass flow (total mass flow 70g∕s)

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Figure 6

Velocity profiles employed for the CIVB analysis. The slight increase of the tangential velocity V near the centerline converts the stable configuration in a CIVB prone case.

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Figure 7

The source term of the azimuthal vorticity transport equation in the stable regime near the flashback limit: (a) stretching/tilting; (b) volume expansion; (c) baroclinic torque

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Figure 8

Influence of the equivalence ratio change from Φ=0.67 (black lines) to Φ=0.83 (red lines): (a) stretching/tilting; (b) volume expansion; (c) baroclinic torque

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Figure 9

Streamlines for Φ=0.67 and for Φ=0.83

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Figure 10

Interaction between turbulence and chemistry, stable configuration (c: reaction progress)

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Figure 11

Interaction between turbulence and chemistry, unstable configuration (c: reaction progress)

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Figure 12

Comparison of experimental and numerical results: velocity profiles in the propagating bubble

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Figure 13

Comparison of experimental and numerical results: flashback limits

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Figure 14

Sketch of the effects leading to Combustion Induced Vortex Breakdown



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