Large Eddy Simulation and Dynamic Mode Decomposition of Turbulent Mixing Layers

Turbulent mixing layers are canonical flow in nature and engineering, and deserve comprehensive studies under various conditions using different methods. In this paper, turbulent mixing layers are investigated using large eddy simulation and dynamic mode decomposition. The accuracy of the computations is verified and validated. Standard dynamic mode decomposition is utilized to flow decomposition, reconstruction and prediction. It was found that the dominant-mode selection criterion based on mode amplitude is more suitable for turbulent mixing layer flow compared with the other three criteria based on singular value, modal energy and integral modal amplitude, respectively. For the mixing layer with random disturbance, the standard dynamic mode decomposition method could accurately reconstruct and predict the region before instability happens, but is not qualified in the regions after that, which implies that improved dynamic mode decomposition methods need to be utilized or developed for the future dynamic mode decomposition of turbulent mixing layers.

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Mixed Acoustic-Entropy Combustion Instabilities in a Model Aeronautical Combustor: Large Eddy Simulation and Reduced Order Modeling

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4037960 ◽

2017 ◽

Vol 140 (3) ◽

Cited By ~ 6

Author(s):

Florent Lacombe ◽

Yoann Méry

Keyword(s):

Large Eddy Simulation ◽

Diffusion Flame ◽

Combustion Process ◽

Premixed Flame ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Combustion Instabilities ◽

Eddy Simulation ◽

Mode Decomposition ◽

Large Eddy

This article focuses on combustion instabilities (CI) driven by entropy fluctuations which is of great importance in practical devices. A simplified geometry is introduced. It keeps the essential features of an aeronautical combustion chamber (swirler, dilution holes, and outlet nozzle), while it is simplified sufficiently to ease the analysis (rectangular vane, one row of holes of the same diameter, no diffuser at the inlet of the chamber, and circular nozzle at the outlet). A large eddy simulation (LES) is carried out on this geometry and the limit cycle of a strong CI involving the convection of an entropy spot is obtained. The behavior of the instability is analyzed using phenomenological description and classical signal analysis. One shows that the system can be better described by considering two reacting zones: a rich mainly premixed flame is located downstream of the swirler and an overall lean diffusion flame is stabilized next to the dilution holes. In a second step, dynamic mode decomposition (DMD) is used to visualize, analyze, and model the complex phasing between different processes affecting the reacting zones. Using these data, a zero-dimensional (0D) modeling of the premixed flame and of the diffusion flame is proposed. These models provide an extended understanding of the combustion process in an aeronautical combustor and could be used or adapted to address mixed acoustic-entropy CI in an acoustic code.

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Mixed Acoustic-Entropy Combustion Instabilities in a Model Aeronautical Combustor: Large Eddy Simulation and Reduced Order Modeling

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2017-64191 ◽

2017 ◽

Author(s):

Florent Lacombe ◽

Yoann Mery

Keyword(s):

Large Eddy Simulation ◽

Diffusion Flame ◽

Combustion Process ◽

Premixed Flame ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Combustion Instabilities ◽

Eddy Simulation ◽

Mode Decomposition ◽

Large Eddy

This article focuses on Combustion Instabilities (CI) driven by entropy fluctuations which is of great importance in practical devices. A simplified geometry is introduced. It keeps the essential features of an aeronautical combustion chamber (swirler, dilution holes, outlet nozzle) while it is simplified sufficiently to ease the analysis (rectangular vane, one row of holes of the same diameter, no diffuser at the inlet of the chamber, circular nozzle at the outlet). A Large Eddy Simulation (LES) is carried out on this geometry and the limit cycle of a strong CI involving the convection of an entropy spot is obtained. The behavior of the instability is analyzed using phenomenological description and classical signal analysis. One shows that the system can be better described by considering two reacting zones: a rich mainly premixed flame is located downstream of the swirler and an overall lean diffusion flame is stabilized next to the dilution holes. In a second step, Dynamic Mode Decomposition (DMD) is used to visualize, analyze and model the complex phasing between the different processes affecting the reacting zones. Using these data, a 0D modeling of the premixed flame and of the diffusion flame is proposed. These models provides an extended understanding of the combustion process in an aeronautical combustor and could be used or adapted to address mixed acoustic-entropy CI in an acoustic code.

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Large Eddy Simulation and Extended Dynamic Mode Decomposition of Flow-Flame Interaction in a Lean Premixed Low Swirl Stabilized Flame

Flow Turbulence and Combustion ◽

10.1007/s10494-014-9560-6 ◽

2014 ◽

Vol 93 (3) ◽

pp. 505-519 ◽

Cited By ~ 8

Author(s):

H. Carlsson ◽

C. Carlsson ◽

L. Fuchs ◽

X. S. Bai

Keyword(s):

Large Eddy Simulation ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Eddy Simulation ◽

Mode Decomposition ◽

Large Eddy ◽

Lean Premixed ◽

Extended Dynamic

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Identification of Noise Sources in a Realistic Turbofan Rotor Using Large Eddy Simulation

Acoustics ◽

10.3390/acoustics2030037 ◽

2020 ◽

Vol 2 (3) ◽

pp. 691-706

Author(s):

Pavel Kholodov ◽

Stéphane Moreau

Keyword(s):

Large Eddy Simulation ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Noise Sources ◽

Trailing Edge ◽

Trailing Edge Noise ◽

Eddy Simulation ◽

Mode Decomposition ◽

Edge Radiation ◽

Large Eddy

Large Eddy Simulation is performed using the NASA Source Diagnostic Test turbofan at approach conditions (62% of the design speed). The simulation is performed in a periodic domain containing one fan blade (rotor-alone configuration). The aerodynamic and acoustic results are compared with experimental data. The dilatation field and the dynamic mode decomposition (DMD) are employed to reveal the noise sources around the rotor. The trailing-edge radiation is effective starting from 50% of span. The strongest DMD modes come from the tip region. Two major noise contributors are shown, the first being the tip noise and the second being the trailing-edge noise. The Ffowcs Williams and Hawkings’ (FWH) analogy is used to compute the far-field noise from the solid surface of the blade. The analogy is computed for the full blade, for its tip region (outer 20% of span) and for lower 80% of span to see the contribution of the latter. The acoustics spectrum below 6 kHz is dominated by the tip part (tip noise), whereas the rest of the blade (trailing-edge noise) contributes more beyond that frequency.

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Analysis and Modelling of Entropy Modes in a Realistic Aeronautical Gas Turbine

Volume 1A: Combustion, Fuels and Emissions ◽

10.1115/gt2013-94224 ◽

2013 ◽

Author(s):

Emmanuel Motheau ◽

Franck Nicoud ◽

Yoann Mery ◽

Thierry Poinsot

Keyword(s):

Transfer Functions ◽

Acoustic Mode ◽

Dynamic Mode Decomposition ◽

Dynamic Mode ◽

Acoustic Coupling ◽

Eddy Simulation ◽

Mode Decomposition ◽

Exit Nozzle ◽

Large Eddy ◽

Aero Engines

A combustion instability in a combustor typical of aero-engines is analyzed and modeled thanks to a low order Helmholtz solver. A Dynamic Mode Decomposition (DMD) is first applied to the Large Eddy Simulation (LES) database. The mode with the highest amplitude shares the same frequency of oscillation as the experiment (approx. 350 Hz) and it shows the presence of large entropy spots generated within the combustion chamber and convected down to the exit nozzle. The lowest purely acoustic mode being in the range 650–700 Hz, it is postulated that the instability observed around 350 Hz stems from a mixed entropy/acoustic mode where the acoustic generation associated with the entropy spots being convected throughout the choked nozzle plays a key role. A Delayed Entropy Coupled Boundary Condition is then derived in order to account for this interaction in the framework of a Helmholtz solver where the baseline flow is assumed at rest. When fed with appropriate transfer functions to model the entropy generation and convection from the flame to the exit, the Helmholtz solver proves able to predict the presence of an unstable mode around 350 Hz, in agreement with both the LES and the experiments. This finding supports the idea that the instability observed in the combustor is indeed driven by the entropy/acoustic coupling.

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