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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Multiphase Flow Large-Eddy Simulation Study of the Fuel Split Effects on Combustion Instabilities in an Ultra-Low-NOx Annular Combustor

[+] Author and Article Information
M. Bauerheim

CERFACS,
42 Avenue Gaspard Coriolis,
Toulouse 31057, France;
SNECMA Villaroche,
Reau 77550, France
e-mail: bauerheim@cerfacs.fr

T. Jaravel

CERFACS,
42 Avenue Gaspard Coriolis,
Toulouse 31057, France;
SNECMA Villaroche,
Reau 77550, France

L. Esclapez

CERFACS,
42 Avenue Gaspard Coriolis,
Toulouse 31057, France;
SNECMA Villaroche,
Reau 77550, France

E. Riber, L. Y. M. Gicquel, B. Cuenot

CERFACS,
42 Avenue Gaspard Coriolis,
Toulouse 31057, France

M. Cazalens

SAFRAN TECH,
Moissy-Cramayel 77550, France;

S. Bourgois, M. Rullaud

SNECMA Villaroche,
Reau 77550, France

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 4, 2015; final manuscript received September 24, 2015; published online November 17, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(6), 061503 (Nov 17, 2015) (8 pages) Paper No: GTP-15-1392; doi: 10.1115/1.4031871 History: Received August 04, 2015; Revised September 24, 2015

This paper describes the application of a coupled acoustic model/large-eddy simulation approach to assess the effect of fuel split on combustion instabilities in an industrial ultra-low-NOx annular combustor. Multiphase flow LES and an analytical model (analytical tool to analyze and control azimuthal modes in annular chambers (ATACAMAC)) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: (1) a gaseous type in the multipoint zone (MPZ) where acoustics generates vortex shedding, which then wrinkle the flame front, and (2) a multiphase flow type in the pilot zone (PZ) where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the PZ and mechanism 2) to assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using an analytical model validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations in the PZ, which strongly depend on the fuel split parameter. However, the correlation between acoustics and the global (pilot + multipoint) heat release fluctuations highlights no dependency on the fuel split staging. It suggests that vortex shedding in the MPZ, almost not depending on the fuel split, is the main feature controlling the flame dynamics for this engine.

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Figures

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Fig. 1

Tools developed at CERFACS for combustion instabilities: low-order models (ATACAMAC), Helmholtz simulations (AVSP), and large eddy simulations (AVBP)

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Fig. 2

Block diagram showing mechanisms 1 (vortex shedding ω̂) and 2 (fuel oscillations φ̂), leading to heat release oscillations q̂

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Fig. 3

The ultra-low-NOx annular configuration LEMCOTEC with N = 19 identical sectors. Network model for ATACAMAC (C0—left) and a complete configuration with detailed swirlers for LES (C2—right).

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Fig. 4

Single sector of the industrial ultra-low-NOx configuration LEMCOTEC

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Fig. 5

ATACAMAC results of the first three azimuthal modes of the LEMCOTEC configuration with N = 19 burners and passive flames: normalized frequency (top), pressure plots over the azimuthal direction (middle), and pressure fields in annular cavities (bottom)

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Fig. 6

Stability maps obtained by ATACAMAC for the first and second azimuthal modesofthe annular engine versus varying FTFu amplitudes (nu = 0.25–1.0) and phase lags (Δϕu=0 –2π)

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Fig. 7

Mesh around the swirler, PZ and MPZ. Details of the swirler and injection system have been blanked.

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Fig. 8

Instantaneous flame nature (premixed or nonpremixed), for the case α = 10%, identified using the fuel mass fraction field and isocontours of heat release (thin lines) and the stoichiometric lines (φ=1, large lines)

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Fig. 9

Isocontours of heat release colored by temperature (top), isocontour of fuel mass fraction (rich, middle), and (lean + reach, bottom) to visualize the flame shape as well as the pilot (middle) and multipoint (bottom) flames versus the fuel split parameter: 5% (left), 10% (middle), and 20% (right)

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Fig. 10

Q-criterion (left) and gaseous fuel oscillations (RMS values, right) in the longitudinal cut plane. Both the multipoint and pilot mean flames (isocontour of the mean heat release) are superimposed in solid black lines.

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Fig. 11

Normalized relative pressure P′̃=p′/p′max and fuel mass fraction Ykero′̃=Ykero′/p′max oscillations in the PZ for the case at α = 10% and forcing frequencies f = 1.0 (left) and f = 1.84 (right). A filter at the forcing frequency is applied to remove hydrodynamic and turbulent oscillations.

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Fig. 12

Normalized relative pressure P′̃ and fuel mass fractions Ykero′̃ oscillations for the case at f = 1.84 and fuel splits α = 5% (left), α = 10% (middle), and α = 20% (right). Normalized phase-lags Δϕ/2π between fuel and pressure oscillations are extracted.

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Fig. 13

Phase lags associated with the pilot gaseous fuel oscillations (Δϕ, left), and the global flame dynamics (pilot + multipoint, ΔϕQ, right) for cases forced at f = 1.0 and 1.84 and fuel split α = 5%, 10%, and 20%

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