scholarly journals CFD predictions of Swirl burner aerodynamics with variable outlet configurations

2019 ◽  
pp. 31-43 ◽  
Author(s):  
Hesham Baej
Keyword(s):  
Recirculation Zone ◽  
Chemical Species ◽  
Swirl Burner ◽  
Low Velocity ◽  
Lean Premixed Combustion ◽  
Active Chemical ◽  
Lean Premixed ◽  
Swirling Flame ◽  
Recirculation Zones ◽  
Reduction Of Nox

Swirl stabilised combustion is one of the most widely used techniques for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of swirl, burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. Therefore, in this paper swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic swirl burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using several gaseous blends at a constant power output. The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by the blend and infer that it is governed by both the shear layer surrounding the Central Recirculation Zones (CRZ) and the gas composition.

Investigation on Non-Premixed Swirling Flame in a Multi-Hole Burner

2011 ◽  
Vol 347-353 ◽  
pp. 2428-2431
Author(s):  
Bing Ge ◽  
Shu Sheng Zang ◽  
Pei Qing Guo
Keyword(s):  
Recirculation Zone ◽  
Reverse Flow ◽  
Swirl Burner ◽  
Mean Velocity ◽  
Swirling Jet ◽  
Swirl Combustion ◽  
Fuel Jet ◽  
Expansion Angle ◽  
Swirling Flame ◽  
Development And Validation

This paper focuses on investigating the flow structures in a multi-hole swirl burner. Using the Particle Image Velocimetry(PIV) technique, the experiment measured the velocity distributions of the swirling flame in a muti-hole burner. The experiments show that there is a central recirculation zone (CRZ) in the middle of the flow field, and two counter-rotating vortices exist along the centerline symmetrically. With fuel jet increase: the width of recirculating zone and axial mean velocity peaks changes little; length of recirculation zone and the biggest reverse flow velocity increases; the expansion angle of swirling jet increase at first, and then changes little; axial non-uniform coefficient of outlet reduces at first, and then increases. With airflow velocity increase: axial mean velocity peaks increase; the dimension of recirculating zone and the expansion angle of swirling jet are unchanged; axial non-uniform coefficient of outlet increases.The data from this experiment is helpful for optimization of the swirl burner design, and can be established as benchmarks for the development and validation of swirl combustion numerical simulations.

Flow recirculation zone length and shear rate are differentially affected by stenosis severity in human coronary arteries

2013 ◽  
Vol 304 (4) ◽  
pp. H559-H566 ◽  
Author(s):  
Ashkan Javadzadegan ◽  
Andy S. C. Yong ◽  
Michael Chang ◽  
Austin C. C. Ng ◽  
John Yiannikas ◽  
...  
Keyword(s):  
Shear Rate ◽  
Coronary Arteries ◽  
Recirculation Zone ◽  
Fluid Dynamic ◽  
Zone Length ◽  
Flow Recirculation ◽  
Stenosis Severity ◽  
Recirculation Zones ◽  
The Relationship

Flow recirculation zones and shear rate are associated with distinct pathogenic biological pathways relevant to thrombosis and atherogenesis. The interaction between stenosis severity and lesion eccentricity in determining the length of flow recirculation zones and peak shear rate in human coronary arteries in vivo is unclear. Computational fluid dynamic simulations were performed under resting and hyperemic conditions on computer-generated models and three-dimensional (3-D) reconstructions of coronary arteriograms of 25 patients. Boundary conditions for 3-D reconstructions simulations were obtained by direct measurements using a pressure-temperature sensor guidewire. In the computer-generated models, stenosis severity and lesion eccentricity were strongly associated with recirculation zone length and maximum shear rate. In the 3-D reconstructions, eccentricity increased recirculation zone length and shear rate when lesions of the same stenosis severity were compared. However, across the whole population of coronary lesions, eccentricity did not correlate with recirculation zone length or shear rate ( P = not signficant for both), whereas stenosis severity correlated strongly with both parameters ( r = 0.97, P < 0.001, and r = 0.96, P < 0.001, respectively). Nonlinear regression analyses demonstrated that the relationship between stenosis severity and peak shear was exponential, whereas the relationship between stenosis severity and recirculation zone length was sigmoidal, with an apparent threshold effect, demonstrating a steep increase in recirculation zone length between 40% and 60% diameter stenosis. Increasing stenosis severity and lesion eccentricity can both increase flow recirculation and shear rate in human coronary arteries. Flow recirculation is much more sensitive to mild changes in the severity of intermediate stenoses than is peak shear.

Simplified Models for NOx Production Rates in Lean-Premixed Combustion

1994 ◽  
Author(s):  
David G. Nicol ◽  
Philip C. Malte ◽  
Robert C. Steele
Keyword(s):  
Laboratory Data ◽  
Chemical Reactor ◽  
Premixed Combustion ◽  
Empirical Correlations ◽  
Simplified Models ◽  
Reactor Modeling ◽  
Lean Premixed Combustion ◽  
Co Concentration ◽  
Lean Premixed ◽  
Recent Laboratory

Simplified models for predicting the rate of production of NOx in lean-premixed combustion are presented. These models are based on chemical reactor modeling, and are influenced strongly by the nitrous oxide mechanism, which is an important source of NOx in lean-premixed combustion. They include 1) the minimum set of reactions required for predicting the NOx production, and 2) empirical correlations of the NOx production rate as a function of the CO concentration. The later have been developed for use in an NOx post-processor for CFD codes. Also presented are recent laboratory data, which support the chemical rates used in this study.

scholarly journals Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

1998 ◽  
Author(s):  
Rajiv Mongia ◽  
Robert Dibble ◽  
Jeff Lovett
Keyword(s):  
Power Spectrum ◽  
Mole Fraction ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

Development and Application of an Eight-Step Global Mechanism for CFD and CRN Simulations of Lean-Premixed Combustors

2007 ◽  
Author(s):  
Igor V. Novosselov ◽  
Philip C. Malte
Keyword(s):  
Chemical Reactor ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Lean Premixed Combustion ◽  
Chemical Reactor Network ◽  
Elevated Pressures ◽  
Nitric Oxide Formation ◽  
No Formation ◽  
Lean Premixed ◽  
Reactor Network

In this paper, the development of an eight-step global chemical kinetic mechanism for methane oxidation with nitric oxide formation in lean-premixed combustion at elevated pressures is described and applied. In particular, the mechanism has been developed for use in computational fluid dynamics (CFD) and chemical reactor network (CRN) simulations of combustion in lean-premixed gas turbine engines. Special attention is focused on the ability of the mechanism to predict NOx and CO exhaust emissions. Applications of the eight-step mechanism are reported in the paper, all for high-pressure, lean-premixed, methane-air (or natural gas-air) combustion. The eight steps of the mechanism are as follows: 1. Oxidation of the methane fuel to CO and H2O. 2. Oxidation of the CO to CO2. 3. Dissociation of the CO2 to CO. 4. Flame NO formation by the Zeldovich and nitrous oxide mechanisms. 5. Flame NO formation by the prompt and NNH mechanisms. 6. Post-flame NO formation by equilibrium H-atom attack on equilibrium N2O. 7. Post-flame NO formation by equilibrium O-atom attack on equilibrium N2O. 8. Post-flame Zeldovich NO formation by equilibrium O-atom attack on N2.

Numerical Simulation of Turbulent Combustion Flows for Coaxial Jet Cluster Burner

2013 ◽  
Author(s):  
Keita Yunoki ◽  
Tomoya Murota ◽  
Keisuke Miura ◽  
Teruyuki Okazaki
Keyword(s):  
Turbulent Combustion ◽  
High Efficiency ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Gas Temperature ◽  
Lean Premixed Combustion ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Lean Premixed ◽  
Multiple Holes

We have developed a burner for the gas turbine combustor, which was high efficiency and low environmental load. This burner is named the “coaxial jet cluster burner” and, as the name indicates, it has multiple fuel nozzles and holes in a coaxial arrangement. To form lean premixed combustion, this burner mixes fuel and air in the multiple holes rapidly. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing. However, the combustion field coexisting with premixed and non-premixed combustion is complicated. The phenomena that occur in the combustion field should be understood in detail. Therefore, we have developed the hybrid turbulent combustion (HTC) model to calculate the form in which non-premixed flame coexists with premixed flame. Turbulent flow has been simulated using a large eddy simulation (LES) with a dynamic sub grid scale (SGS) model coupled with the HTC model. These models were programmed to a simulation tool based on the OpenFOAM library. However, there were unclear points about their applicability to an actual machine evaluation and the predictive precision of CO concentration which affects burner performance. In this study, we validate the HTC model by comparing its results with measured gas temperature and gas concentration distributions obtained with a coaxial jet cluster burner test rig under atmospheric pressure. In addition, we analyze the CO generation mechanism for the lean premixed combustion in the burner.

Direct Numerical Simulation of Partial Fuel Stratification Assisted Lean Premixed Combustion for Assessment of Hybrid G-Equation/Well-Stirred Reactor Model

2021 ◽  
Author(s):  
Chao Xu ◽  
Muhsin Ameen ◽  
Pinaki Pal ◽  
Sibendu Som
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Initial Conditions ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Lean Premixed Combustion ◽  
Fuel Stratification ◽  
Stirred Reactor ◽  
Lean Premixed ◽  
Flame Structures

Abstract Partial fuel stratification (PFS) is a promising fuel injection strategy to stabilize lean premixed combustion in spark-ignition (SI) engines. PFS creates a locally stratified mixture by injecting a fraction of the fuel, just before spark timing, into the engine cylinder containing homogeneous lean fuel/air mixture. This locally stratified mixture, when ignited, results in complex flame structure and propagation modes similar to partially premixed flames, and allows for faster and more stable flame propagation than a homogeneous lean mixture. This study focuses on understanding the detailed flame structures associated with PFS-assisted lean premixed combustion. First, a two-dimensional direct numerical simulation (DNS) is performed using detailed fuel chemistry, experimental pressure trace, and realistic initial conditions mapped from a prior engine large-eddy simulation (LES), replicating practical lean SI operating conditions. DNS results suggest that conventional triple flame structures are prevalent during the initial stage of flame kernel growth. Both premixed and non-premixed combustion modes are present with the premixed mode contributing dominantly to the total heat release. Detailed analysis reveals the effects of flame stretch and fuel pyrolysis on the flame displacement speed. Based on the DNS findings, the accuracy of a hybrid G-equation/well-stirred reactor (WSR) combustion model is assessed for PFS-assisted lean operation in the LES context. The G-equation model qualitatively captures the premixed branches of the triple flame, while the WSR model predicts the non-premixed branch of the triple flame. Finally, potential needs for improvements to the hybrid G-equation/WSR modeling approach are discussed.

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