Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner with Central Bluff Body

Abstract Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bi-stable. This bi-stable behaviour, which can be triggered via a small change in some of the controlling parameters, for example the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. This has impact on combustion dynamics, emissions and pressure losses. While several experimental investigations exist on this topic, numerical analysis is limited. The present work is therefore also of numerical nature, with a two-fold scope: a) simulation and validation with experiments of the bi-stable flame behaviour via Computational Fluid Dynamics (CFD) in the form of Large Eddy Simulation (LES) and b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counter-intuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. The counter-intuitive presence of a lifted flame is explained here in terms of the phase averaged data which show that the flame apex is not placed at the centre of the spinning reverse flow region. It is instead slightly shifted radially outward where the axial velocity recovers to low positive values of the order of the turbulent burning rate. A simple one-dimensional flame stabilization model is applied to explain this peculiar flame behaviour. This model provides first an estimation of the flame radius of curvature in terms of axial velocity and turbulence quantities. This radius is therefore used to determine the total flux of reactants into the flame, given by an axial convection and a radial diffusion contributions. Subsequently the possibility of the flame positioned at the centre of the vortex is excluded based on the balance between this flux and the turbulent burning rate. A clear explanation of the mechanism leading to the sudden flame jump has instead not been identified and only some hypotheses are provided.

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Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner With Central Bluff Body

10.1115/1.0002508v ◽

2021 ◽

Author(s):

Fernando Biagioli ◽

Alessandro Innocenti ◽

teresa marchione ◽

Steffan Terhaar

Keyword(s):

Numerical Analysis ◽

Bluff Body ◽

Turbulent Flames ◽

Swirl Burner

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Numerical Modeling of Stationary But Developing Premixed Turbulent Flames

Volume 1: Combustion and Fuels, Education ◽

10.1115/gt2006-90916 ◽

2006 ◽

Author(s):

Pratap Sathiah ◽

Andrei N. Lipatnikov

Keyword(s):

Bluff Body ◽

Burning Velocity ◽

Rectangular Channel ◽

Turbulent Flame ◽

Flame Stabilization ◽

Turbulent Flames ◽

Turbulent Diffusivity ◽

Flame Thickness ◽

Premixed Turbulent Flames ◽

Premixed Turbulent Flame

A typical stationary premixed turbulent flame is the developing flame, as indicated by the growth of mean flame thickness with distance from flame-stabilization point. The goal of this work is to assess the importance of modeling flame development for RANS simulations of confined stationary premixed turbulent flames. For this purpose, submodels for developing turbulent diffusivity and developing turbulent burning velocity, which were early suggested by our group (FSC model) and validated for expanding spherical flames [4], have been incorporated into the so-called Zimont model of premixed turbulent combustion and have been implemented into the CFD package Fluent 6.2. The code has been run to simulate a stationary premixed turbulent flame stabilized behind a triangular bluff body in a rectangular channel using both the original and extended models. Results of these simulations show that the mean temperature and velocity fields in the flame are markedly affected by the development of turbulent diffusivity and burning velocity.

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Partially Premixed Flame Stabilization in the Presence of a Combined Swirl and Bluff Body Influenced Flowfield: An Experimental Investigation

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4046965 ◽

2020 ◽

Vol 142 (7) ◽

Author(s):

Rajesh Sadanandan ◽

Aritra Chakraborty ◽

Vinoth Kumar Arumugam ◽

Satyanarayanan R. Chakravarthy

Keyword(s):

Flow Field ◽

Bluff Body ◽

Reverse Flow ◽

Fluid Dynamic ◽

Thermal Power ◽

Swirl Flow ◽

Flame Stabilization ◽

Dynamic Strain ◽

Low Velocity ◽

Divergent Flow

Abstract Optical and laser diagnostic measurements in a nonpremixed model gas turbine (GT) burner have been performed to investigate the effect of an increase in thermal power on the flame stabilization. The model GT burner has a large bluff body base with an annular swirl region, leading to a convergent-divergent flow field at the burner exit. Under the investigated conditions, the flame stabilizes predominantly in the diverging section characterized by the swirl flow with a central recirculation zone. With increasing thermal power, the reverse flow of hot burned gases is strengthened, with the hydroxyl radical (OH) planar laser induced fluorescence (PLIF) images indicating an increase in the temperature of the burned gases. The preferred flame stabilization location coincides with the inner shear layer between the reactant inflow and the reverse flow of hot burned gases. At high thermal power, the flame seems to stabilize in regions of high fluid dynamic strain rate, highlighting the influence of the reverse flowing burned gases in the evolution of the flammable mixture upstream. However, simultaneous and time-resolved measurements of the flow-field and scalar field are needed for direct quantification of this. The results are in agreement with the flame stabilization theories based on partial fuel-air mixing and streamline divergence. The flow is seen to decelerate upstream of the flame front and the flame stabilizes in a region of low velocity, created as a result of heat release diverging the streamlines ahead of it.

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Effect of Air Pressure and Gutter Angle on Flame Stability and DeZubay Number for Methane-Air Combustion

International Journal of Turbo and Jet Engines ◽

10.1515/tjj-2016-0018 ◽

2017 ◽

Vol 34 (1) ◽

Cited By ~ 1

Author(s):

S. Boopathi ◽

P. Maran

Keyword(s):

High Speed ◽

Pressure Range ◽

Bluff Body ◽

Apex Angle ◽

Flame Stabilization ◽

Air Pressure ◽

Flame Stability ◽

Stability Chart ◽

Stable Flame

AbstractThe combustion at high speed reactants requires a flame holding characteristics to sustain the flame in the afterburner. The flame holding characteristics of the combustor is carried out by the bluff-body stabilizers. The range of conditions of parameters influencing the flame stabilization is to be identified and the effects on the flame sustainability have to be investigated. DeZubay used the concept of DeZubay number and flame stability envelope to determine the stabilization and blowout range. In the present work, the effect of air pressure and the angle of apex of the V-gutter on flame stabilization and blowout mechanism have been experimentally investigated for six different apex angles and four different air pressure conditions. The value of DeZubay number at each condition has been calculated and verified with DeZubay stability chart for flame stabilization. The results show that stable flame is obtained for the entire pressure range when the apex angle of the V gutter is in 60° and 90°.

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Experimental Investigations on the Effect of Swirl and Bluff Body Wake in Circular Jets

Volume 2: Fora ◽

10.1115/fedsm2006-98008 ◽

2006 ◽

Author(s):

R. Senthil ◽

N. V. Mahalakshmi

Keyword(s):

Bluff Body ◽

Combustion Efficiency ◽

Flame Stabilization ◽

Recirculation Region ◽

Experimental Investigations ◽

Reynolds Stresses ◽

Circular Jets ◽

Air Mixing ◽

High Reynolds ◽

Bluff Body Wake

Swirl with bluff body wake in jets finds application in gas turbine engines, turbo machinery etc. to strengthen the recirculation region, improve combustion efficiency, enhance flame stabilization, improve fuel air mixing and blow off limits and lower pollutant formation. This paper discusses the combined effect of swirl and rotating bluff body wake in circular jets. The flow pattern of the swirl jet has been studied in the near vicinity of the jet exit for different inlet high Reynolds numbers (only for which the recirculation effect is beneficial), critical swirl angle (30 degree-similar to what is employed in industrial furnaces and burners), and a constant blockage ratio of the bluff body at eight different axial positions in the recirculation zone. Reynolds stresses, mean axial and tangential velocities, turbulent intensities, turbulent kinetic energy are measured and compared for the bluff body rotating and non-rotating cases. A DANTEC Dynamics make constant temperature anemometer with X-probe has been used to measure mean and turbulence parameters.

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Computational and Experimental Analysis of a Compact Combustor Integrated into a JetCat P90 RXi

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4051348 ◽

2021 ◽

Author(s):

Daniel Holobeny ◽

Brian T. Bohan ◽

Marc D. Polanka

Keyword(s):

Bluff Body ◽

Flame Stabilization ◽

Inlet Temperature ◽

Gas Temperature ◽

Turbine Engine ◽

Pressure Losses ◽

Primary Zone ◽

Sustained Operation ◽

Mass Flow Rates ◽

Stable Flame

Abstract Ultra Compact Combustors (UCC) look to reduce the overall combustor length and weight in modern gas turbine engines. Previously, a UCC achieved self-sustained operation at sub-idle speeds in a JetCat P90 RXi turbine engine with a length savings of 33% relative to the stock combustor. However, that combustor experienced flameout as reactions were pushed out of the primary zone before achieving mass flow rates at the engine's idle condition. A new combustor that utilized a bluff body flame stabilization with a larger combustor volume looked to keep reactions in the primary zone within the same axial dimensions. This design was investigated computationally for generalized flow patterns, pressure losses, exit temperature profiles, and reaction distributions at three engine power conditions. The computational results showed the validity of this new Ultra Compact Combustor, with a turbine inlet temperature of 1080 K and a pattern factor of 0.67 at the cruise condition. The combustor was then built and tested in the JetCat P90 RXi with rotating turbomachinery and gaseous propane fuel. The combustor maintained a stable flame from ignition through the 36,000 RPM idle condition. The engine ran self-sustained from 25,000 to 36,000 RPM with an average exit gas temperature of 980 K, which is comparable to the stock engine.

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