Effects of Outlet Boundary Conditions on the Reacting Flow Field in a Swirl-Stabilized Burner at Dry and Humid Conditions

2012 ◽  
Author(s):  
Steffen Terhaar ◽  
Bernhard C. Bobusch ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Measurement Techniques ◽  
Theoretical Explanation ◽  
Clear Correlation ◽  
Reacting Flow ◽  
Flow State ◽  
Swirl Number ◽  
Emission Analysis ◽  
Exit Boundary

During the design and testing process of swirl-stabilized combustors, it is often impractical to maintain identical outlet boundary conditions. Furthermore, it is a common practice to intentionally change the acoustic boundary conditions of the outlet in order to suppress thermoacoustic instabilities. In the presented work the susceptibility of the reacting flow field to down-stream perturbations is assessed by the application of an area contraction at the outlet. Since combustion and fuel composition are shown to be important parameters for the influence of the boundary conditions on the flow field, highly steam diluted flames are investigated in addition to dry flames, at different equivalence ratios and degrees of swirl. The applied measurement techniques include Particle Image Velocimetry, Laser Doppler Velocimetry, and emission analysis. The results reveal a clear correlation of the susceptibility of the flow field to downstream perturbations to both, the inlet swirl number and the amount of dilatation caused by the flame. The concept of an effective swirl number down-stream of the flame is applied to the results and is proven to be the dominating parameter. A theoretical explanation for the influence of this parameter is provided by the usage of the well known theory of subcritical and supercritical swirling flows, where perturbations can propagate upstream solely in subcritical flows via standing waves. Knowledge of the flow state is of particular importance for the evaluation of combustion tests with differing exit boundary conditions and the results emphasize the need for realistic exit boundary conditions for numerical simulations.

Effects of Outlet Boundary Conditions on the Reacting Flow Field in a Swirl-Stabilized Burner at Dry and Humid Conditions

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Steffen Terhaar ◽  
Bernhard C. Bobusch ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Measurement Techniques ◽  
Theoretical Explanation ◽  
Clear Correlation ◽  
Reacting Flow ◽  
Flow State ◽  
Swirl Number ◽  
Emission Analysis ◽  
Exit Boundary

During the design and testing process of swirl-stabilized combustors, it is often impractical to maintain identical outlet boundary conditions. Furthermore, it is a common practice to intentionally change the acoustic boundary conditions of the outlet in order to suppress thermoacoustic instabilities. In the presented work the susceptibility of the reacting flow field to downstream perturbations is assessed by the application of an area contraction at the outlet. Since combustion and fuel composition are shown to be important parameters for the influence of the boundary conditions on the flow field, highly steam diluted flames are investigated in addition to dry flames at different equivalence ratios and degrees of swirl. The applied measurement techniques include particle image velocimetry, laser doppler velocimetry, and emission analysis. The results reveal a clear correlation of the susceptibility of the flow field to downstream perturbations to both the inlet swirl number and the amount of dilatation caused by the flame. The concept of an effective swirl number downstream of the flame is applied to the results and is proven to be the dominating parameter. A theoretical explanation for the influence of this parameter is provided by the usage of the well known theory of subcritical and supercritical swirling flows, where perturbations can propagate upstream solely in subcritical flows via standing waves. Knowledge of the flow state is of particular importance for the evaluation of combustion tests with differing exit boundary conditions and the results emphasize the need for realistic exit boundary conditions for numerical simulations.

Multiple Flow Patterns and Heat Transfer in Confined Jet Impingement

2002 ◽  
Author(s):  
X. Li ◽  
J. L. Gaddis ◽  
T. Wang
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Boundary Conditions ◽  
Jet Impingement ◽  
Flow Patterns ◽  
Computational Results ◽  
Initial Flow ◽  
Flow Parameters ◽  
Visualization Experiment ◽  
Exit Boundary

The flow field of a 2-D laminar confined impinging slot jet is investigated. Numerical results indicate that there exist two different solutions in some range of geometric and flow parameters. The two steady flow patterns are obtained under identical boundary conditions but only with different initial flow fields. Three different exit boundary conditions are investigated to eliminate artificial effects. The different flow patterns are observed to significantly affect the heat transfer. A flow visualization experiment is carried out to verify the computational results and both flow patterns are observed. The bifurcation mechanism is interpreted and discussed.

Response Dynamics of Recirculation Structures in Coaxial Nonpremixed Swirl-Stabilized Flames Subjected to Acoustic Forcing

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Uyi Idahosa ◽  
R. Santhosh ◽  
Ankur Miglani ◽  
Saptarshi Basu
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Fluid Dynamic ◽  
High Energy ◽  
Reacting Flow ◽  
Flow State ◽  
Response Dynamics ◽  
Jet Flame ◽  
Flame Response ◽  
Acoustic Forcing

This paper reports the time-mean and phase-locked response of nonreacting as well as reacting flow field in a coaxial swirling jet/flame (nonpremixed). Two distinct swirl intensities plus two different central pipe flow rates at each swirl setting are investigated. The maximum response is observed at the 105 Hz mode in the range of excitation frequencies (0–315 Hz). The flow/flame exhibited minimal response beyond 300 Hz. It is seen that the aspect ratio change of inner recirculation zone (IRZ) under nonreacting conditions (at responsive modes) manifests as a corresponding increase in the time-mean flame aspect ratio. This is corroborated by ∼25% decrease in the IRZ transverse width in both flame and cold flow states. In addition, 105 Hz excited states are found to shed high energy regions (eddies) asymmetrically when compared to dormant 315 Hz pulsing frequency. The kinetic energy (KE) of the flow field is subsequently reduced due to acoustic excitation and a corresponding increase (∼O (1)) in fluctuation intensity is witnessed. The lower swirl intensity case is found to be more responsive than the high swirl case as in the former flow state the resistance offered by IRZ to incoming acoustic perturbations is lower due to inherently low inertia. Next, the phase-locked analysis of flow and flame structure is employed to further investigate the phase dependence of flow/flame response. It is found that the asymmetric shifting of IRZ mainly results at 270 deg acoustic forcing. The 90 deg phase angle forcing is observed to convect the IRZ farther downstream in both swirl cases as compared to other phase angles. The present work aims primarily at providing a fluid dynamic view point to the observed nonpremixed flame response without considering the confinement effects.

Experimental Investigation of a RQL Burner With Jet in Cross Flow Fuel Injection: Characterization of the Reacting Flow Field at Realistic Operating Conditions

2019 ◽  
Author(s):  
T. Soworka ◽  
T. Behrendt ◽  
C. Hassa ◽  
J. Heinze ◽  
E. Magens ◽  
...  
Keyword(s):  
Flow Field ◽  
Fuel Injection ◽  
Measurement Techniques ◽  
Cross Flow ◽  
Mie Scattering ◽  
Operating Conditions ◽  
Reacting Flow ◽  
Axial Location ◽  
Primary Zone ◽  
Jet In Cross Flow

Abstract Future rich-burn/quick-quench/lean-burn (RQL) burners for aero engines face the challenge to further reduce the emission of soot. Alternative ways of fuel injection are therefore in the focus of modern RQL combustion systems. This contribution aims to investigate experimentally the influence of fuel injection on the reacting flow field, with the emphasis on soot production in the primary zone. For the test, a Rolls-Royce prototype burner was used in two different configurations which differ only in the axial location of jet in cross flow fuel injection and thereby provoke different ways of fuel atomization. In the upstream configuration the burner features characteristics of a pre-filming airblast atomizer. Whereas with the fuel tip in downstream position solely Jet-in-Cross-Flow fuel atomisation is expected. The burner was tested at realistic aero engine combustor conditions (p30 = 9.28 bar, T30 = 603 K, AFR = 7.6). Several optical measurement techniques were used to characterise the reacting flow field. Their difficult application in a rich burn environment is described briefly. The structure of the reacting flow field is illustrated by Particle-Image-Velocimetry (PIV). Planar Mie scattering and Planar Laser-Induced Fluorescence (PLIF) are used to characterise the placement of liquid and gaseous fuel respectively. The location and structure of heat release zones are captured in terms of OH* and CO2* chemiluminescence. Finally Laser-Induced-Incandescence (LII) is used to obtain three dimensional soot distributions in the primary zone. On this basis 20% less soot was measured for the upstream configuration at the axial location of maximal soot concentration. This remarkable difference could be attributed to the different placement of liquid fuel and the resulting better mixing.

Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection

2014 ◽  
Author(s):  
Thoralf G. Reichel ◽  
Steffen Terhaar ◽  
Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
High Speed ◽  
Flame Temperature ◽  
Air Injection ◽  
Reacting Flow ◽  
Nox Emissions ◽  
Test Rig ◽  
Swirl Number ◽  
Lean Premixed

Since lean premixed combustion allows for fuel-efficiency and low emissions, it is nowadays state of the art in stationary gas turbines. In the long term, it is also a promising approach for aero engines, when safety issues like lean blowout (LBO) and flame flashback in the premixer can be overcome. While for the use of hydrogen the LBO limits are extended, the flashback propensity is increased. Thus, axial air injection is applied in order to eliminate flashback in a swirl-stabilized combustor burning premixed hydrogen. Axial injection constitutes a non-swirling jet on the central axis of the radial swirl generator which influences the vortex breakdown position. In the present work changes in the flow field and their impact on flashback limits of a model combustor are evaluated. First, a parametric study is conducted under isothermal test conditions in a water tunnel employing particle image velocimetry (PIV). The varied parameters are the amount of axially injected air and swirl number. Subsequently, flashback safety is evaluated in the presence of axial air injection in an atmospheric combustor test rig and a stability map is recorded. The flame structure is measured using high-speed OH* chemiluminescence imaging. Simultaneous high-speed PIV measurements of the reacting flow provide insight in the time-resolved reacting flow field and indicate the flame location by evaluating the Mie scattering of the raw PIV images by the means of the Qualitative Light Sheet (QLS) technique. The isothermal tests identify the potential of axial air injection to overcome the axial velocity deficits at the nozzle outlet, which is considered crucial in order to provide flashback safety. This effect of axial air injection is shown to prevail in the presence of a flame. Generally, flashback safety is shown to benefit from an elevated amount of axial air injection and a lower swirl number. Note, that the latter also leads to increased NOx emissions, while axial air injection does not. Additionally, fuel momentum is indicated to positively influence flashback resistance, although based on a different mechanism, an explanation of which is suggested. In summary, flashback-proof operation of the burner with a high amount of axial air injection is achieved on the whole operating range of the test rig at inlet temperatures of 620 K and up to stoichiometric conditions while maintaining single digit NOx emissions below a flame temperature of 2000 K.

scholarly journals Local Measurements in a Three Dimensional Jet-Stabilized Model Combustor

1995 ◽  
Author(s):  
H. J. Bauer ◽  
L. Eigenmann ◽  
B. Scherrer ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
Modular Design ◽  
Numerical Models ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Internal Heat ◽  
Flame Stabilization ◽  
Laser Doppler Velocimeter ◽  
Reacting Flow ◽  
Primary Zone

Measurements of velocity, temperature and species concentration in a three dimensional jet-stabilized combustor are presented. The modular design of the combustor permits the use of either gaseous or liquid fuels. For the investigations presented here, fuel oil has been chosen which is atomized by an air-blast atomizer. Access to the reacting flow field for probes as well as for non intrusive optical measurement techniques is provided by several windows along the combustor axis. Velocity measurements in the mixing zone and even in the primary zone of the combustor are performed by means of a two-component Laser Doppler Velocimeter (LDA). Platinum rhodium/platinum thermocouples (PtRh/Pt) specially designed for reduced internal heat losses are used for the investigation of the temperature field. A cranked, water cooled probe is employed in order to detect local species concentrations. The experimental results reveal detailed information about the characteristics of the reacting flow field. The interaction of fuel atomization and flame stabilization in the primary zone is illustrated by a direct comparison with experimental data of the gaseous fuel case investigated earlier [ 1 ]. The results gained here serve as an excellent database to verify numerical models for the description of liquid spray combustion.

Increasing Flashback Resistance in Lean Premixed Swirl-Stabilized Hydrogen Combustion by Axial Air Injection

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Thoralf G. Reichel ◽  
Steffen Terhaar ◽  
Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
High Speed ◽  
Flame Temperature ◽  
Air Injection ◽  
Reacting Flow ◽  
Nox Emissions ◽  
Test Rig ◽  
Swirl Number ◽  
Lean Premixed

Since lean premixed combustion allows for fuel-efficiency and low emissions, it is nowadays state of the art in stationary gas turbines. In the long term, it is also a promising approach for aero engines, when safety issues like lean blowout (LBO) and flame flashback in the premixer can be overcome. While for the use of hydrogen the LBO limits are extended, the flashback propensity is increased. Thus, axial air injection is applied in order to eliminate flashback in a swirl-stabilized combustor burning premixed hydrogen. Axial injection constitutes a nonswirling jet on the central axis of the radial swirl generator which influences the vortex breakdown (VB) position. In the present work, changes in the flow field and their impact on flashback limits of a model combustor are evaluated. First, a parametric study is conducted under isothermal test conditions in a water tunnel employing particle image velocimetry (PIV). The varied parameters are the amount of axially injected air and swirl number. Subsequently, flashback safety is evaluated in the presence of axial air injection in an atmospheric combustor test rig and a stability map is recorded. The flame structure is measured using high-speed OH* chemiluminescence imaging. Simultaneous high-speed PIV measurements of the reacting flow provide insight in the time-resolved reacting flow field and indicate the flame location by evaluating the Mie scattering of the raw PIV images by means of the qualitative light sheet (QLS) technique. The isothermal tests identify the potential of axial air injection to overcome the axial velocity deficits at the nozzle outlet, which is considered crucial in order to provide flashback safety. This effect of axial air injection is shown to prevail in the presence of a flame. Generally, flashback safety is shown to benefit from an elevated amount of axial air injection and a lower swirl number. Note that the latter also leads to increased NOx emissions, while axial air injection does not. Additionally, fuel momentum is indicated to positively influence flashback resistance, although based on a different mechanism, an explanation of which is suggested. In summary, flashback-proof operation of the burner with a high amount of axial air injection is achieved on the whole operating range of the test rig at inlet temperatures of 620 K and up to stoichiometric conditions while maintaining single digit NOx emissions below a flame temperature of 2000 K.

CFD prediction of the reacting flow field inside a subscale scramjetcombustor

1988 ◽  
Author(s):  
T. CHITSOMBOON ◽  
G. NORTHAM ◽  
R. ROGERS ◽  
G. DISKIN
Keyword(s):  
Flow Field ◽  
Reacting Flow
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