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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Numerical Simulations of Isothermal Flow in a Swirl Burner

[+] Author and Article Information
M. García-Villalba, W. Rodi

Institute for Hydromechanics, University of Karlsruhe, Karlsruhe, 76128 Germany

J. Fröhlich

Institute for Technical Chemistry and Polymer Chemistry, University of Karlsruhe, Karlsruhe, 76128 Germany

J. Eng. Gas Turbines Power 129(2), 377-386 (Feb 01, 2006) (10 pages) doi:10.1115/1.2364198 History: Received October 01, 2005; Revised February 01, 2006

In this paper, the non-reacting flow in a swirl burner is studied using large eddy simulation. The configuration consists of two unconfined coannular jets at a Reynolds number of 81,500. The flow is characterized by a Swirl number of 0.93. Two cases are studied in the paper differing with respect to the axial location of the inner pilot jet. It was observed in a companion experiment (Bender and Büchner, 2005, Proc. 12 Int. Cong. Sound and Vibration, Lisbon, Portugal) that when the inner jet is retracted the flow oscillations are considerably amplified. This is also found in the present simulations. Large-scale coherent structures rotating at a constant rate are observed when the inner jet is retracted. The rotation of the structures leads to vigorous oscillations in the velocity and pressure time signals recorded at selected points in the flow. In addition, the mean velocities, the turbulent fluctuations, and the frequency of the oscillations are in good agreement with the experiments. A conditional averaging procedure is used to perform a detailed analysis of the physics leading to the low-frequency oscillations.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the burner (taken from (11))

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Figure 2

Numerical setup and boundary conditions. Color represents mean axial velocity.

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Figure 6

Radial profiles of RMS velocity xpilot=0. (a) Axial velocity. (b) Tangential velocity. Symbols, experiments (11). Lines, LES.

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Figure 7

Radial profiles of RMS velocity xpilot=−0.73R. (a) Axial velocity. (b) Tangential velocity. Symbols, experiments (11). Lines, LES.

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Figure 8

Fluctuating kinetic energy: (a)xpilot=0 and (b)xpilot=−0.73R

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Figure 11

Power spectrum of axial velocity fluctuations at x∕R=0.1, r∕R=0.73. Solid line, experiment (11)xpilot=−0.73R. Dashed line, simulation xpilot=−0.73R. Dash-dotted line, simulation xpilot=0.

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Figure 13

Illustration of the conditional average procedure. Color according to p−⟨p⟩. The black circle indicates the points where the minimum of the pressure is looked for. The other circle (further outward) indicates the outer radius of the burner.

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Figure 14

Coherent structures obtained using the conditional average flow field. (a) Iso-surface pc−⟨p⟩=−0.1. Color as in Fig. 9. (b) Iso-surfaces uxc−⟨ux⟩=0.3 and uxc−⟨ux⟩=0.3.

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Figure 16

Two-dimensional cut through the plane y∕R=0 of the conditional-averaged flow. Color is given by pc. Pseudo-streamlines calculated using uxc and urc. Thick black line uxc=0.

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Figure 17

Conditional-averaged velocity profiles at x∕R=0.1. (a) Pressure. (b) Axial velocity. (c) Tangential velocity.

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Figure 3

Streamlines of the average flow in an axial plane (a)xpilot=0 and (b)xpilot=−0.73R

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Figure 4

Radial profiles of mean velocity xpilot=0. (a) Axial velocity. (b) Tangential velocity. Symbols, experiments (11). Lines, LES.

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Figure 5

Radial profiles of mean velocity xpilot=−0.73R. (a) Axial velocity. (b) Tangential velocity. Symbols, experiments (11). Lines, LES.

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Figure 9

Coherent structures visualized using an iso-surface of pressure fluctuations. Left, xpilot=0. Right, xpilot=−0.73R. (a,b,d)p−⟨p⟩=−0.3. (c)p−⟨p⟩=−0.15. Color as explained in the text.

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Figure 10

Time signal of axial velocity at x∕R=0.1, r∕R=0.73 recorded during the simulations. (a)xpilot=0. (b)xpilot=−0.73R.

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Figure 12

Amplitude of the power spectrum at the fundamental frequency fpeak at x∕R=0.1 as a function of r∕R for case xpilot=−0.73R. (a) Experiment (11). (b) Simulation.

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Figure 15

Two-dimensional cut through the plane x∕R=0.1 of the conditional-averaged flow. Color is given by pc. Pseudo-streamlines calculated using urc and uθc. Thick black line uxc=0.

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Figure 18

Two-dimensional cut through the plane x∕R=0.1 of the conditional-averaged flow. Color is given by pc−⟨p⟩. Pseudo-streamlines calculated using urc−⟨ur⟩ and uθc−⟨uθ⟩. Thick black line uxc=0.

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