scholarly journals A Comparison of the Characteristics of Planar and Axisymmetric Bluff-Body Combustors Operated under Stratified Inlet Mixture Conditions

2013 ◽  
Vol 2013 ◽  
pp. 1-15
Author(s):  
G. Paterakis ◽  
K. Souflas ◽  
E. Dogkas ◽  
P. Koutmos
Keyword(s):  
Large Scale ◽  
Cross Correlation ◽  
Bluff Body ◽  
Fuel Injection ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Control Measures ◽  
Effective Control ◽  
Large Eddy ◽  
Flame Region

The work presents comparisons of the flame stabilization characteristics of axisymmetric disk and 2D slender bluff-body burner configurations, operating with inlet mixture stratification, under ultralean conditions. A double cavity propane air premixer formed along three concentric disks, supplied with a radial equivalence ratio gradient the afterbody disk recirculation, where the first flame configuration is stabilized. Planar fuel injection along the center plane of theleading faceof a slender square cylinder against the approach cross-flow results in a stratified flame configuration stabilized alongside the wake formation region in the second setup. Measurements of velocities, temperatures,OH∗andCH∗chemiluminescence, local extinction criteria, and large-eddy simulations are employed to examine a range of ultralean and close to extinction flame conditions. The variations of the reacting front disposition within these diverse reacting wake topologies, the effect of the successive suppression of heat release on the near flame region characteristics, and the reemergence of large-scale vortical activity on approach to lean blowoff (LBO) are investigated. The cross-correlation of the performance of these two popular flame holders that are at the opposite ends of current applications might offer helpful insights into more effective control measures for expanding the operational margin of a wider range of stabilization configurations.

scholarly journals Control of a Nosocomial Outbreak of COVID-19 in a University Hospital

2020 ◽  
Vol 7 (12) ◽  
Author(s):  
Sei Harada ◽  
Shunsuke Uno ◽  
Takayuki Ando ◽  
Miho Iida ◽  
Yaoko Takano ◽  
...  
Keyword(s):  
High Risk ◽  
Large Scale ◽  
Secondary Infection ◽  
Control Measures ◽  
University Hospital ◽  
Contact Tracing ◽  
Effective Control ◽  
Primary Case ◽  
Pcr Screening ◽  
Social Distancing

Abstract Background Nosocomial spread of coronavirus disease 2019 (COVID-19) causes clusters of infection among high-risk individuals. Controlling this spread is critical to reducing COVID-19 morbidity and mortality. We describe an outbreak of COVID-19 in Keio University Hospital, Japan, and its control and propose effective control measures. Methods When an outbreak was suspected, immediate isolation and thorough polymerase chain reaction (PCR) testing of patients and health care workers (HCWs) using an in-house system, together with extensive contact tracing and social distancing measures, were conducted. Nosocomial infections (NIs) were defined as having an onset or positive test after the fifth day of admission for patients and having high-risk contacts in our hospital for HCWs. We performed descriptive analyses for this outbreak. Results Between March 24 and April 24, 2020, 27 of 562 tested patients were confirmed positive, of whom 5 (18.5%) were suspected as NIs. For HCWs, 52 of 697 tested positive, and 40 (76.9%) were considered NIs. Among transmissions, 95.5% were suspected of having occurred during the asymptomatic period. Large-scale isolation and testing at the first sign of outbreak terminated NIs. The number of secondary cases directly generated by a single primary case found before March 31 was 1.74, compared with 0 after April 1. Only 4 of 28 primary cases generated definite secondary infection; these were all asymptomatic. Conclusions Viral shedding from asymptomatic cases played a major role in NIs. PCR screening of asymptomatic individuals helped clarify the pattern of spread. Immediate large-scale isolation, contact tracing, and social distancing measures were essential to containing outbreaks.

Large Eddy Simulation and Experimental Analysis of Combustion Dynamics in a Gas Turbine Burner

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Daniel Moëll ◽  
Andreas Lantz ◽  
Karl Bengtson ◽  
Daniel Lörstad ◽  
Annika Lindholm ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Flame Temperature ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Large Eddy Simulations ◽  
Combustion Dynamics ◽  
Flamelet Generated Manifold ◽  
Large Eddy ◽  
Gas Turbine Burner

Large eddy simulations (LES) and experiments (planar laser-induced fluorescence of the hydroxyl radical (OH-PLIF) and pressure transducer) have been carried out on a gas turbine burner fitted to an atmospheric combustion rig. This burner, from the Siemens SGT-800 gas turbine, is a low NOx, partially premixed burner, where preheat air temperature, flame temperature, and pressure drop across the burner are kept similar to engine full load conditions. The large eddy simulations are based on a flamelet-generated manifold (FGM) approach for representing the chemistry and the Smagorinsky model for subgrid turbulence. The experimental data and simulation data are in good agreement, both in terms of time averaged and time-resolved quantities. From the experiments and LES, three bands of frequencies of pressure fluctuations with high power spectral density are found in the combustion chamber. The first two bands are found to be axial pressure modes, triggered by coherent flow motions from the burner, such as the flame stabilization location and the precessing vortex core (PVC). The third band is found to be a cross flow directional mode interacting with two of the four combustion chamber walls in the square section of the combustion chamber, triggered from general flow motions. This study shows that LES of real gas turbine components is feasible and that the results give important insight into the flow, flame, and acoustic interactions in a specific combustion system.

scholarly journals Ecosystem services provision by gully control. A review

2019 ◽  
Vol 45 (1) ◽  
pp. 333 ◽  
Author(s):  
A. Romero-Díaz ◽  
E. Díaz-Pereira ◽  
J. De Vente
Keyword(s):  
Ecosystem Services ◽  
Water Conservation ◽  
Large Scale ◽  
Cost Benefit ◽  
Control Measures ◽  
Effective Control ◽  
Cost Benefit Ratio ◽  
Cultural Ecological ◽  
The Cost ◽  
Gully Control

Gully erosion causes severe damage to crops and infrastructures and affects the provision of ecosystem services worldwide. To assess the potential of gully control measures to protect ecosystem services and assess the conditions required for their large-scale implementation, this paper critically evaluates a range of gully control measures documented in the World Overview of Conservation Approaches and Technologies (WOCAT). Environmental and socio-economic impacts of technologies are assessed, as well as the implications for ecosystem services, costs and benefits of implementation, and stakeholder’s perception. It is demonstrated how gully control measures provide notable on-site and off-site benefits for socio-economic, cultural, ecological, and production goals, and to protect crucial ecosystem services. Control measures particularly contribute to soil and water conservation and to regulating ecosystem services by controlling soil erosion, water cycling, and natural hazards. Most effective control measures consist of combined vegetative and structural measures and of catchment wide interventions. While implementation of gully control can initially be expensive, on the long term, the cost-benefit ratio is usually positive. Moreover, the results emphasize the importance of evaluating control measures considering monetary aspects and all ecosystem services they provide. Nevertheless, individual farmers can often not afford the implementation and maintenance costs due to barriers for implementation and therefore require sustained institutional support. 

scholarly journals Large Eddy Simulation of a Bluff Body Stabilized Lean Premixed Flame

2014 ◽  
Vol 2014 ◽  
pp. 1-18 ◽  
Author(s):  
A. Andreini ◽  
C. Bianchini ◽  
A. Innocenti
Keyword(s):  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Turbulent Combustion ◽  
Bluff Body ◽  
Sensitivity Study ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Lean Premixed

The present study is devoted to verify current capabilities of Large Eddy Simulation (LES) methodology in the modeling of lean premixed flames in the typical turbulent combustion regime of Dry LowNOxgas turbine combustors. A relatively simple reactive test case, presenting all main aspects of turbulent combustion interaction and flame stabilization of gas turbine lean premixed combustors, was chosen as an affordable test to evaluate the feasibility of the technique also in more complex test cases. A comparison between LES and RANS modeling approach is performed in order to discuss modeling requirements, possible gains, and computational overloads associated with the former. Such comparison comprehends a sensitivity study to mesh refinement and combustion model characteristic constants, computational costs, and robustness of the approach. In order to expand the overview on different methods simulations were performed with both commercial and open-source codes switching from quasi-2D to fully 3D computations.

Chemical Herbicides and Forestation

1970 ◽  
Vol 46 (6) ◽  
pp. 458-465 ◽  
Author(s):  
R. F. Sutton
Keyword(s):  
Weed Control ◽  
Large Scale ◽  
Control Measures ◽  
Effective Control ◽  
Plantation Establishment ◽  
Weed Growth ◽  
Weeds Control ◽  
Mammalian Toxicity

Weeds commonly impair the growth of forest crop trees. Control measures rely increasingly on herbicides, large-scale use of which dates from the development of chlorophenoxyacetic herbicides in the 1940's. Weed control is not to kill weeds but to divert growth resources into crop trees. The herbicide tool becomes increasingly powerful and versatile because of new herbicides and new ways of using them. Of the organic herbicides, only phenols have high mammalian toxicity. It is highly improbable that problems could arise from use of herbicides in normal forestry operations. Herbicides make available to crop trees nutrients that would otherwise be taken up by weeds and those that are released by killed weeds. Control measures are especially important during plantation establishment. Grasses and herbs, and woody weeds are the main types of weed growth. Effective control measures may be devised for almost any situation.

Large-Eddy Simulation of Shaped Hole Film Cooling with the Influence of Cross Flow

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Wang Qingsong ◽  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Large Scale ◽  
High Efficiency ◽  
Cross Flow ◽  
Vortex Pair ◽  
Hairpin Vortices ◽  
Eddy Simulation ◽  
Large Eddy ◽  
End Wall

AbstractIn the highly-loaded turbine blade passage, cross flow is driven by the lateral gradient. It strongly influences the cooling performances in the endwall region. In this research, the effect of cross flow on the shaped film cooling hole is studied by Large Eddy Simulation (LES); modal analysis is conducted with an incremental POD (iPOD) approach, which makes the analysis of the large data sets from LES feasible. It is shown that the symmetry of the counter rotating vortex pair (CRVP) is destroyed. The large-scale vortex induced by end-wall cross flow plays an important role in both shape and convection of hairpin vortices and horseshoe vortices, which influences the coolant distribution. This study suggests that the effects of cross flow should be considered for the design of end-wall film cooling. It also indicates the high efficiency of the iPOD approach, which can be used to analyze large amounts of high-dimensional data.

scholarly journals Scalar Measurements in Bluff Body Stabilized Flames Using Cars Diagnostics

1991 ◽  
Author(s):  
J. C. Pan ◽  
M. D. Vangsness ◽  
S. P. Heneghan ◽  
D. R. Ballal
Keyword(s):  
Turbulence Intensity ◽  
Large Scale ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Gradient Diffusion ◽  
Stirred Reactor ◽  
Flame Region ◽  
Layer Region

Measurements of mean and rms temperature fluctuations were performed in confined turbulent premixed methane-air flames, stabilized on a conical flameholder. A CARS system was used for these measurements. These tests employed flameholders of different blockage ratios (13% and 25%), and mixtures with different equivalence ratios (0.56, 0.65, 0.8, and 0.9) and approach turbulence intensity (2%, 17%, and 22%). It was found that the recirculation zone closely resembles a perfectly well-stirred reactor. Blockage ratio, equivalence ratio, or approach turbulence intensity did not alter the scalar field. The turbulent flame structure enveloping the recirculation zone comprises: (i) an ignition/thin flame region in the vicinity of the flameholder base, (ii) a reacting shear layer region of large-scale coherent structures, and (iii) a thick flame region where entrainment is the dominant mechanism. Finally, analysis suggests that the scalar gradient-diffusion relationship is valid and areas of non-gradient diffusion, if any, are probably small.

A Review of Mechanisms Controlling Bluff-Body Stabilized Flames With Closely-Coupled Fuel Injection

2011 ◽  
Author(s):  
Jeffery A. Lovett ◽  
Caleb Cross ◽  
Eugene Lubarsky ◽  
Ben T. Zinn
Keyword(s):  
Liquid Fuel ◽  
Bluff Body ◽  
Fuel Injection ◽  
Flame Structure ◽  
Flame Stabilization ◽  
Current Understanding ◽  
Two Phase ◽  
Combustion Region ◽  
Combustion Systems ◽  
And Performance

The processes controlling bluff-body stabilized combustion have been extensively studied over the years because such stabilization approaches are commonly used in many practical systems. Much of the current understanding of this problem was attained in experimental and analytical studies of premixed combustion systems where the complexities introduced by fuel atomization, vaporization and mixing could be neglected. Yet, practical considerations often require fuel injection just upstream of the bluff-body stabilized combustion region. Consequently, it’s necessary to develop understanding of the fundamental processes in such non-premixed systems. Supplying fuel via the injection of discrete liquid fuel jets requires understanding of the complex physics of two-phase sprays and the transport to various regions within the combustor. This paper describes current understanding of the manner in which these processes affect flame stabilization in bluff-body combustion systems that employ close-coupled, liquid fuel injection. Specifically, the paper compares findings of premixed bluff-body flames with recent results obtained in studies using close-coupled fueling at Georgia Tech to support postulates of the processes controlling flame stabilization and flame structure. These findings are also used to propose a set of parameters that can be used to describe the combustion behavior and performance of such combustion systems.

Ignition and Flame Stabilization of a Premixed Jet in Hot Cross Flow

2013 ◽  
Author(s):  
Denise Schmitt ◽  
Michael Kolb ◽  
Johannes Weinzierl ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Equivalence Ratio ◽  
Large Scale ◽  
Large Diameter ◽  
Flame Temperature ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Wide Range ◽  
Cold Case

At the Institute of Thermodynamics, Technical University of Munich a large scale atmospheric combustion test rig has been designed and set up. The experimental setup is comprised of two burning zones: A first zone consists of 16 burners providing vitiated air at 1776K, into which a secondary fuel-air mixture jet is injected and ignited by the hot cross flow. The phenomenon is known in the literature as a reacting jet in hot cross flow. The hot data is compared to the cold case in order to show differences in the flow field due to flame propagation. For evaluating the flow field several experimental analyses have been applied so far (OH*, High-Speed PIV, Mixture Analysis). The focus of this paper is on the momentum ratios J = 4–10 with Jet Reynolds Numbers between 20,000 and 80,000. For the cold case the flow field is measured and compared with the reacting jet. In the injector the air and the natural gas are perfectly premixed. The equivalence ratio of the jet is varied over a wide range of mixtures (ϕ = 0.05–0.77) resulting in an adiabatic flame temperature of the jet between 800 and 2200K. As the pictures of the chemiluminescence analysis show the jet gas ignites immediately upon entering the hot cross flow. The distinct influence of the equivalence ratio on the flame length and shape can be seen in the data. The trajectory of the flame penetrates further into the channel compared to the trajectory of the cold case caused by the reaction in the flame and its resulting gas expansion. Due to the large diameter of the jet in the experiment the origins of the dominant flow patterns are obtained with high spatial resolution. Following this, flame anchoring mechanisms at different operation points are derived.

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