Flow, mixing, and flame stabilization in bluff-body burner with decreased central jet velocity

2021 ◽  
Vol 33 (6) ◽  
pp. 067122
Author(s):  
Jieli Wei ◽  
Qing Xie ◽  
Jian Zhang ◽  
Zhuyin Ren
Keyword(s):  
Bluff Body ◽  
Flame Stabilization ◽  
Flow Mixing ◽  
Jet Velocity

Review and Analysis of Bluff Body Flame Stabilization Data

2008 ◽  
Author(s):  
Sajjad A. Husain ◽  
Ganesh Nair ◽  
Santosh Shanbhogue ◽  
Tim C. Lieuwen
Keyword(s):  
Activation Energy ◽  
Kinetic Modeling ◽  
First Principles ◽  
Bluff Body ◽  
Large Range ◽  
Flame Stabilization ◽  
Local Extinction ◽  
Data Set ◽  
Flame Sheet ◽  
Semi Empirical

This paper compiles and analyzes bluff body stabilized flame blowoff data from the literature. Many of these studies contain semi-empirical blowoff correlations that are, in essence, Damko¨hler number correlations of their data. This paper re-analyzes these data, utilizing various Damko¨hler number correlations based upon detailed kinetic modeling for determining chemical time scales. While the results from this compilation are similar to that deduced from many earlier studies, it demonstrates that a rather comprehensive data set taken over a large range of conditions can be correlated from “first-principles” based calculations that do not rely on empirical fits or adjustable constants (e.g., global activation energy or pressure exponents). The paper then discusses the implications of these results on understanding of blowoff. Near blowoff flames experience local extinction of the flame sheet, manifested as “holes” that form and convect downstream. However, local extinction is distinct from blowoff — in fact, under certain conditions the flame can apparently persist indefinitely with certain levels of local extinction. We hypothesize that simple Damko¨hler number correlations contain the essential physics describing this first stage of blowoff; i.e., they are correlations for the conditions where local extinction on the flame begins, but do not fundamentally describe the ultimate blowoff condition itself. However, such correlations are reasonably successful in correlating blowoff limits because the ultimate blowoff event appears to be correlated to some extent to the onset of this first stage.

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

1994 ◽  
Author(s):  
Z. Gu ◽  
M. A. R. Sharif
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Flame Stabilization ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Combustion Chambers ◽  
Recirculating Flow ◽  
Conservative Form ◽  
Curvilinear Grid ◽  
Predictor Corrector

Abstract The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

scholarly journals Dynamics of lean premixed flames stabilized on a meso-scale bluff-body in an unconfined flow field

2018 ◽  
Vol 13 (6) ◽  
pp. 48 ◽  
Author(s):  
Yu Jeong Kim ◽  
Bok Jik Lee ◽  
Hong G. Im
Keyword(s):  
Bluff Body ◽  
Proper Time ◽  
Premixed Flames ◽  
Narrow Channel ◽  
Flame Stabilization ◽  
Inflow Velocity ◽  
Lean Premixed Flames ◽  
Lean Premixed ◽  
The Mean ◽  
Meso Scale

Two-dimensional direct numerical simulations were conducted to investigate the dynamics of lean premixed flames stabilized on a meso-scale bluff-body in hydrogen-air and syngas-air mixtures. To eliminate the flow confinement effect due to the narrow channel, a larger domain size at twenty times the bluff-body dimension was used in the new simulations. Flame/flow dynamics were examined as the mean inflow velocity is incrementally raised until blow-off occurs. As the mean inflow velocity is increased, several distinct modes in the flame shape and fluctuation patterns were observed. In contrast to our previous study with a narrow channel, the onset of local extinction was observed during the asymmetric vortex shedding mode. Consequently, the flame stabilization and blow-off behavior was found to be dictated by the combined effects of the hot product gas pocket entrained into the extinction zone and the ability to auto-ignite the mixture within the given residence time corresponding to the lateral flame fluctuations. A proper time scale analysis is attempted to characterize the flame blow-off mechanism, which turns out to be consistent with the classic theory of Zukoski and Marble.

scholarly journals A Model for Bluff Body Flame Stabilization

1986 ◽  
Author(s):  
J. A. De Champlain ◽  
M. F. Bardon
Keyword(s):  
Experimental Data ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Laminar Flame ◽  
Flame Stabilization ◽  
Effect Of Temperature ◽  
Laminar Flame Speed ◽  
Tabular Form ◽  
Chemical Effects ◽  
Stirred Reactor

Previous work on bluff body stabilization mechanisms is reviewed, and existing models are categorized in tabular form, showing the underlying assumptions and resulting equations. Lacunae in existing models are discussed, particularly their reliance on characteristics such as laminar flame speed which is difficult to predict for the conditions encountered in turbojet afterburners. A model for bluff body flame stabilization is proposed based on the stirred reactor approach. In addition to the effect of temperature, pressure and geometry, it includes chemical effects such as vitiation and fuel-air equivalence ratio. Blow off velocities predicted by the model are compared to experimental data for various conditions.

Numerical Modeling of Stationary But Developing Premixed Turbulent Flames

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.

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

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.

The Role of Mean Flame Anchoring on the Stability Characteristics of Syngas, Synthesis Natural Gas, and Hydrogen Fuels in a Turbulent Non-Premixed Bluff-Body Combustor

2019 ◽  
Author(s):  
Nikhil Ashokbhai Baraiya ◽  
Satynarayanan R. Chakravarthy
Keyword(s):  
Natural Gas ◽  
Flow Rate ◽  
Momentum Flux ◽  
Bluff Body ◽  
Flame Stabilization ◽  
Inlet Flow ◽  
Combustion Dynamics ◽  
Flow Rates ◽  
Inlet Flow Rate ◽  
The Difference

Abstract A lab-scale bluff body combustor is mapped for its stability and flame dynamics of non-premixed flames. The characteristics are observed across variations in the fuel composition, as well as in the inlet flow rate. The combustor is seen to exhibit markedly different dynamics for each of the varied fuel compositions. This behavior is explained on the basis of mean flame stabilization behavior and on the combined effects of the fuel-jet momentum flux and global equivalence ratio. It is seen that the H2 flames primarily act as a pilot source for secondary combustion of either CO or CH4. Further, it is seen that, the high momentum flux associated with H2-CO mixtures result in combustion near the wall and outside the bluff-body shear layers at low inlet flow rates. Whereas, at high inlet flow rates, the mean heat release rate is seen to stabilize closer to the injection holes as well as extend to near the bluff-body shear layer. This marked difference in flame stabilization is seen to have a drastic effect on the nature of oscillations inside the chamber. This is contrasted to H2-CH4 (synthesis natural gas) flames that exhibit stabilization inside the bluff-body wake at high inlet flow rate. The difference between H2-CH4 and H2-CO flames with regards to combustion dynamics is then explained as a result of the flame stabilization behavior, which is seen to be different across the varied fuel compositions. While H2-CH4 flame exhibits the well-known large wake structures responsible for combustion instability, H2-CO flame exhibits no such structures, owing to their stabilization point. Further analysis using pressure fixed phase instants reveal the difference in nature of combustion dynamics across the tested fuel compositions and are justified using the spatial Rayleigh index map.

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