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Laser Raman scattering measurements of differential molecular diffusion in nonreacting turbulent jets of H2/CO2 mixing with air (1995)

Smith, L. L. ; Dibble, R. W. ; Talbot, L. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 7 (1995), S. 1455-1466

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: In this paper we report measurements of differential diffusion in nonreacting jet flows. Pulsed laser Raman scattering spectroscopy is used to measure species concentrations in nonreacting jets of H2/CO2 into air over a range of Reynolds numbers from 1000 to 64 000. Measurements are also made in strained laminar opposed flows of H2/CO2 against air, where differential diffusion effects on relative species concentrations are observed to be independent of strain rate. In laminar opposed flows and in a laminar jet (Re=1000), measurements of average species concentrations show significant differential diffusion effects. In jet flows of higher Reynolds numbers, only instantaneous species concentrations are affected by differential diffusion; measured species concentrations are the same, on average, as the species concentrations that would have been observed if all species diffusivities were equal. Instantaneous differential diffusion effects in turbulent jets are quantified by the variance of a differential diffusion variable z, where z is the difference between the normalized mole fractions of H2 and CO2 (and normalization refers to dividing each species mole fraction by the mole fraction of that species in pure jet fluid). Measurements show that zRMS diminishes with increasing Reynolds number. Histograms of z show negative skewness in the low Reynolds number jet. At higher Reynolds numbers the histograms become more symmetric, although asymmetries do remain at higher Reynolds numbers in the data obtained near the jet edge, where there is an interface between jet fluid and coflowing air. © 1995 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.868532

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2

Electronic Resource

Experimental criteria for the determination of fractal parameters of premixed turbulent flames (1992)

Shepherd, I. G. ; Cheng, Robert K. ; Talbot, L.

Springer

Experiments in fluids 13 (1992), S. 386-392

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ISSN: 1432-1114

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The influence of spatial resolution, digitization noise, the number of records used for averaging, and the method of analysis on the determination of the fractal parameters of a high Damköhler number, methane/air, premixed, turbulent stagnation-point flame are investigated in this paper. The flow exit velocity was 5 m/s and the turbulent Reynolds number was 70 based on a integral scale of 3 mm and a turbulent intensity of 7%. The light source was a copper vapor laser which delivered 20 nsecs, 5 mJ pulses at 4 kHz and the tomographic cross-sections of the flame were recorded by a high speed movie camera. The spatial resolution of the images is 155 × 121 μm/pixel with a field of view of 50 × 65 mm. The stepping caliper technique for obtaining the fractal parameters is found to give the clearest indication of the cutoffs and the effects of noise. It is necessary to ensemble average the results from more than 25 statistically independent images to reduce sufficiently the scatter in the fractal parameters. The effects of reduced spatial resolution on fractal plots are estimated by artificial degradation of the resolution of the digitized flame boundaries. The effect of pixel resolution, an apparent increase in flame length below the inner scale rolloff, appears in the fractal plots when the measurent scale is less than approximately twice the pixel resolution. Although a clearer determination of fractal parameters is obtained by local averaging of the flame boundaries which removes digitization noise, at low spatial resolution this technique can reduce the fractal dimension. The degree of fractal isotropy of the flame surface can have a significant effect on the estimation of the flame surface area and hence burning rate from two-dimensional images. To estimate this isotropy a determination of the outer cutoff is required and three-dimensional measurements are probably also necessary.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00223246

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3

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Geotechnical and acoustic characteristics of Plio-Pleistocene sediments from the Hebrides Slope (1994)

Talbot, L. A. ; Paul, M. A. ; Stoker, M. S.

Springer

Geo-marine letters 14 (1994), S. 244-251

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ISSN: 1432-1157

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Geotechnical data from Plio-Pleistocene sediments on the Hebrides Slope provide the basis for an analysis of potential factors controlling their acoustic character as observed on high-resolution seismic reflection profiles. Differences in acoustic signature within the sedimentary succession are related to the void index and thus to soil structure and, in turn, to the depositional history of the sediments. In this example, a correlation can be demonstrated between the seismic and geotechnical stratigraphies.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01274060

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4

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Direct measurement of mixture fraction in reacting flow using Rayleigh scattering (1993)

Goix, P. J. ; Leonard, K. R. ; Talbot, L. ; [et al.]

Springer

Experiments in fluids 15 (1993), S. 247-254

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ISSN: 1432-1114

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The mixture fraction variable, ξ, is very useful in describing reaction zone structure in nonpremixed flames. Extinction limits and turbulent mixing are often described as a function of this variable. Experimental evaluation of ξ is critical for improving our understanding of the influence of turbulent mixing on the chemistry process. Heretofore, the evaluation of mixture fraction in combusting flow required multiple simultaneous concentration measurements. In this paper we present a fuel designed to permit measurements of mixture fraction by Rayleigh scattering technique only. A Rayleigh intensity/mixture fraction correspondence has been obtained experimentally in a laminar coflow flame. The influence of strain rate and differential diffusion effects have been investigated using laminar counterflow diffusion flame and shifting equilibrium chemistry models. The results obtained from comparisons between experiments and these models are very encouraging and suggest that the Rayleigh/mixture fraction correspondence established is valid under both the turbulent mixing and laminar strained flamelet combustion regimes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00223402

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Large-scale control of the retroflection of the Labrador Current (2023)

Jutras, M. ; Dufour, C. ; Planat, N. ; [et al.]

In: XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)

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Publication Date: 2023-07-03

Description: The Labrador Current transports cold, relatively fresh, and well-oxygenated waters within the subpolar North Atlantic and along the western American continental shelf. The contribution to both regions is determined by the strength of the eastward retroflection of the Labrador Current at the Grand Banks. A good understanding of the pathways of the Labrador Current and of their underlying drivers is thus crucial to improve our ability to predict physical and biological changes in the northwestern Atlantic. Here, we investigate the pathways of the Labrador Current using a Machine Learning unsupervised k-means++ clustering method applied to a large set of Lagrangian trajectories. The trajectories are that of virtual particles advected by the velocity field of the GLORYS12V1 ocean reanalysis model. The Labrador Current mainly follows a westward-flowing and an eastward retroflecting pathway (20% and 50% of the flow, respectively) that compensate each other through time in a see-saw behaviour. We develop a retroflection index to investigate the drivers of the retroflection of the Labrador Current. Our analyses reveal that strong retroflection generally occurs when a large-scale circulation adjustment, related to the subpolar gyre, accelerates the Labrador Current and shifts the Gulf Stream northward, partly driven by a northward shift of the zero-wind-stress-curl line in the western North Atlantic. Starting in 2008, a particularly strong northward shift of the Gulf Stream dominates the other drivers. Monitoring winds and circulation around the Grand Banks could thus help predict consequences on marine life in the northwestern Atlantic and to set fishing quotas.

Language: English

Type: info:eu-repo/semantics/conferenceObject

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