Dynamics of Premixed H2/CH4 Flames Under Near Blowoff Conditions

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Qingguo Zhang ◽  
Santosh J. Shanbhogue ◽  
Tim Lieuwen
Keyword(s):  
Strain Rate ◽  
Temporal Dynamics ◽  
Complex Dynamics ◽  
Vortex Breakdown ◽  
Local Strain ◽  
Mie Scattering ◽  
Flame Stabilization ◽  
Local Extinction ◽  
Extinction Events ◽  
Extinction Strain Rate

Swirling flows are widely used in industrial burners and gas turbine combustors for flame stabilization. Several prior studies have shown that these flames exhibit complex dynamics under near blowoff conditions, associated with local flamelet extinction and alteration in the vortex breakdown flow structure. These extinction events are apparently due to the local strain rate irregularly oscillating above and below the extinction strain rate values near the attachment point. In this work, global temporally resolved and detailed spatial measurements were obtained of hydrogen/methane flames. Supporting calculations of extinction strain rates were also performed using detailed kinetics. It is shown that flames become unsteady (or local extinctions happen) at a nearly constant extinction strain rate for different hydrogen/methane mixtures. Based upon analysis of these results, it is suggested that classic Damköhler number correlations of blowoff are, in fact, correlations for the onset of local extinction events, not blowoff itself. Corresponding Mie scattering imaging of near blowoff flames also was used to characterize the spatio-temporal dynamics of holes along the flame that are associated with local extinction.

Dynamics of Premixed H2/CH4 Flames Under Near-Blowoff Conditions

2009 ◽  
Author(s):  
Qingguo Zhang ◽  
Santosh J. Shanbhogue ◽  
Tim Lieuwen
Keyword(s):  
Strain Rate ◽  
Temporal Dynamics ◽  
Complex Dynamics ◽  
Vortex Breakdown ◽  
Local Strain ◽  
Mie Scattering ◽  
Flame Stabilization ◽  
Local Extinction ◽  
Extinction Events ◽  
Extinction Strain Rate

Swirling flows are widely used in industrial burners and gas turbine combustors for flame stabilization. Several prior studies have shown that these flames exhibit complex dynamics under near-blowoff conditions, associated with local flamelet extinction and alteration in the vortex breakdown flow structure. These extinction events are apparently due to the local strain rate irregularly oscillating above and below the extinction strain rate values near the attachment point. In this work, global, temporally resolved and detailed spatial measurements were obtained of hydrogen/methane flames. Supporting calculations of extinction strain rates were also performed using detailed kinetics. It is shown that flames become unsteady (or local extinctions happen) at a nearly constant extinction strain rate for different hydrogen/methane mixtures. Based upon analysis of these results, it is suggested that classic Damkohler number correlations of blowoff are, in fact, correlations for the onset of local-extinction events, not blowoff itself. Corresponding Mie scattering imaging of near-blowoff flames also was used to characterize the spatio-temporal dynamics of holes along the flame that are associated with local extinction.

Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

2015 ◽  
Author(s):  
Hirotatsu Watanabe ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Strain Rate ◽  
Shear Layer ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Flame Stabilization ◽  
Sudden Expansion ◽  
Strain Rates ◽  
Cross Point ◽  
Extinction Strain Rate

Premixed CH4/O2/CO2 flames (oxy-flames) and CH4/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.

Quantitative analysis of in situ straining experiments in the case of strong frictional forces

1978 ◽  
Vol 36 (1) ◽  
pp. 570-571
Author(s):  
F. Louchet ◽  
L.P. Kubin
Keyword(s):  
Strain Rate ◽  
Radiation Effects ◽  
Dislocation Line ◽  
Critical Length ◽  
Local Strain ◽  
Local Flow ◽  
Double Kink ◽  
Dislocation Densities ◽  
Frictional Forces ◽  
Local Strain Rate

Investigation of frictional forces -Experimental techniques and working conditions in the high voltage electron microscope have already been described (1). Care has been taken in order to minimize both surface and radiation effects under deformation conditions.Dislocation densities and velocities are measured on the records of the deformation. It can be noticed that mobile dislocation densities can be far below the total dislocation density in the operative system. The local strain-rate can be deduced from these measurements. The local flow stresses are deduced from the curvature radii of the dislocations when the local strain-rate reaches the values of ∿ 10-4 s-1.For a straight screw segment of length L moving by double-kink nucleation between two pinning points, the velocity is :where ΔG(τ) is the activation energy and lc the critical length for double-kink nucleation. The term L/lc takes into account the number of simultaneous attempts for double-kink nucleation on the dislocation line.

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.

Quantitative Detection of Hydrogen Gas Release during Slow Strain Rate Testing in Aluminum Alloys

2021 ◽  
Vol 1016 ◽  
pp. 568-573
Author(s):  
Keitaro Horikawa ◽  
Michiko Arayama ◽  
Hidetoshi Kobayashi
Keyword(s):  
Aluminum Alloys ◽  
Strain Rate ◽  
Local Strain ◽  
Hydrogen Sensor ◽  
Hydrogen Gas ◽  
Slow Strain Rate ◽  
Image Correlation ◽  
Quantitative Detection ◽  
Gas Release ◽  
Closed Chamber

We have developed a new testing device which is capable of detecting hydrogen gas release during slow strain rate tensile testing (SSRT) under ordinary pressure. The device is composed of an SSRT machine equipped with a closed chamber with an inspection window that is connected to gas chromatography with a semiconductor hydrogen sensor. Local strain distribution in the specimen during the SSRT is monitored dynamically with a digital image correlation (DIC) method. Hydrogen was pre-charged to aluminum alloys by means of friction in water process. Using the device, it was shown that hydrogen was released particularly in the stage of plastic deformation and fracture. In addition, the hydrogen gas release at the moment of fracture was clearly increased when the alloys were hydrogen-charged and tested at a slow strain rate. When we calculated hydrogen gas release from the fracture surface in Al-Zn-Mg base alloys tested at 3.3×10-6 s-1, the hydrogen amount was estimated to be 6.24×10-10 mol /mm2 in a hydrogen-uncharged alloy, and 1.30×10-9 mol / mm2 in a hydrogen-charged alloy.

scholarly journals Temporal dynamics of stomatal conductance of plants under water deficit: can homeostasis be improved by more complex dynamics?

2004 ◽  
Vol 47 (3) ◽  
pp. 423-431 ◽  
Author(s):  
Gustavo Maia Souza ◽  
Ricardo Ferraz de Oliveira ◽  
Victor José Mendes Cardoso
Keyword(s):  
Stomatal Conductance ◽  
Sugar Beet ◽  
Water Deficit ◽  
Time Series Data ◽  
Temporal Dynamics ◽  
Complex Dynamics ◽  
Fractal Dimensions ◽  
Series Data ◽  
Complex Behaviour ◽  
Lz Complexity

In this study we hypothesized that chaotic or complex behavior of stomatal conductance could improve plant homeostasis after water deficit. Stomatal conductance of sunflower and sugar beet leaves was measured in plants grown either daily irrigation or under water deficit using an infrared gas analyzer. All measurements were performed under controlled environmental conditions. In order to measure a consistent time series, data were scored with time intervals of 20s during 6h. Lyapunov exponents, fractal dimensions, KS entropy and relative LZ complexity were calculated. Stomatal conductance in both irrigated and non-irrigated plants was chaotic-like. Plants under water deficit showed a trend to a more complex behaviour, mainly in sunflower that showed better homeostasis than in sugar beet. Some biological implications are discussed.

Mechanical basis for lingual deformation during the propulsive phase of swallowing as determined by phase-contrast magnetic resonance imaging

2007 ◽  
Vol 103 (1) ◽  
pp. 255-265 ◽  
Author(s):  
Samuel M. Felton ◽  
Terry A. Gaige ◽  
Timothy G. Reese ◽  
Van J. Wedeen ◽  
Richard J. Gilbert
Keyword(s):  
Strain Rate ◽  
Phase Contrast ◽  
Compressive Strain ◽  
Local Strain ◽  
Styloid Process ◽  
Tongue Pressure ◽  
Orthogonal Expansion ◽  
Physiological Strain ◽  
Phase Contrast Mri ◽  
Contrast Magnetic Resonance

The tongue is an intricately configured muscular organ that undergoes a series of rapid shape changes intended to first configure and then transport the bolus from the oral cavity to the pharynx during swallowing. To assess the complex array of mechanical events occurring during the propulsive phase of swallowing, we employed tongue pressure-gated phase-contrast MRI to represent the tissue's local strain rate vectors. Validation of the capacity of phase-contrast MRI to represent local compressive and expansive strain rate was obtained by assessing deformation patterns induced by a synchronized mechanical plunger apparatus in a gelatinous material phantom. Physiological strain rate data were acquired in the sagittal and coronal orientations at 0, 200, 400, and 600 ms relative to the gating pulse during 2.5-ml water bolus swallows. This method demonstrated that the propulsive phase of swallowing is associated with a precisely organized series of compressive and expansive strain rate events. At the initiation of propulsion, bolus position resulted from obliquely aligned compressive and expansive strain, vertically aligned compressive strain and orthogonal expansion, and compressive strain aligned obliquely to the styloid process. Bolus reconfiguration and translocation resulted from a combination of compressive strain occurring in the middle and posterior tongue aligned obliquely between the anterior-inferior and the posterior-superior regions with commensurate orthogonal expansion, along with bidirectional contraction in the distribution of the transversus and verticalis muscle fibers. These data support the concept that propulsive lingual deformation is due to complex muscular interactions involving both extrinsic and intrinsic muscles.

A Microscopic Study on Local Strain Rate Sensitivity of Polypropylene Syntactic Foam with Microballoons

2010 ◽  
Vol 160-162 ◽  
pp. 1280-1284
Author(s):  
En Yang Wang ◽  
Masaki Omiya
Keyword(s):  
Strain Rate ◽  
Microscopic Study ◽  
Strain Rate Sensitivity ◽  
Syntactic Foam ◽  
Rate Sensitivity ◽  
Local Strain ◽  
Local Strain Rate

A Microscopic Study on Local Strain Rate Sensitivity of Polypropylene Syntactic Foam with Microballoons

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