On vertical turbulent buoyant jets

So, R. M. C.; Aksoy, Hakan

doi:10.1016/0017-9310(93)90003-o

Cited by 20 publications

(20 citation statements)

References 22 publications

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“…Possible buoyancy effects were omitted. This was justified by the prevailing high Froude numbers [45], indicated by the inlet conditions. Heat transfer due to radiation [46] was also omitted, assuming an adiabatic system.…”

Section: Outline Of the Mathematical And Numerical Modelingmentioning

confidence: 99%

Comparison of Combustion Models for Lifted Hydrogen Flames within RANS Framework

Benim

Pfeiffelmann

2019

Energies

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Within the framework of a Reynolds averaged numerical simulation (RANS) methodology for modeling turbulence, a comparative numerical study of turbulent lifted H 2 /N 2 flames is presented. Three different turbulent combustion models, namely, the eddy dissipation model (EDM), the eddy dissipation concept (EDC), and the composition probability density function (PDF) transport model, are considered in the analysis. A wide range of global and detailed combustion reaction mechanisms are investigated. As turbulence model, the Standard k-ε model is used, which delivered a comparatively good accuracy within an initial validation study, performed for a non-reacting H 2 /N 2 jet. The predictions for the lifted H 2 /N 2 flame are compared with the published measurements of other authors, and the relative performance of the turbulent combustion models and combustion reaction mechanisms are assessed. The flame lift-off height is taken as the measure of prediction quality. The results show that the latter depends remarkably on the reaction mechanism and the turbulent combustion model applied. It is observed that a substantially better prediction quality for the whole range of experimentally observed lift-off heights is provided by the PDF model, when applied in combination with a detailed reaction mechanism dedicated for hydrogen combustion.

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Section: Outline Of the Mathematical And Numerical Modelingmentioning

confidence: 99%

Comparison of Combustion Models for Lifted Hydrogen Flames within RANS Framework

Benim

Pfeiffelmann

2019

Energies

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“…4, corresponding to 0.50, 1.00 and 2.00 m/s slot average velocities, respectively. The existence of intermediate region of the buoyant jet defined by So and Aksoy [8] indicates this situation as the initial momentum flux and the buoyancy flux are of comparable importance.…”

Section: The Buoyant Jet Regionsmentioning

confidence: 99%

“…The earlier study showed that the non-buoyancy region refers to the same region as a jet 'starting length' [7]. Basically, the jets in a quiescent ambient can be classified according to the relative importance of the initial momentum flux and the initial specific buoyancy flux [8]. In addition, it has been found that relative influence of inertia and buoyancy forces resolves the stratified flow characteristics in a room [9].…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation and modelling of a buoyant attached plane jet in a room

Cao¹,

Kurnitski²,

Ruponen³

et al. 2009

Applied Thermal Engineering

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Buoyant attached jets are widely used in various types of supply air devices especially in office buildings. This study focuses on a two-dimensional cooled attached jet characteristic, including mean flow field structure, specification of the jet regions and maximum velocity decay. A new superimposing model is derived to predict the maximum velocity decay and validated by measurement results. The measurement results demonstrate that the intermediate region of a buoyant jet does exist when an inner layer extends downstream of the jet slot. In addition, by assuming that the buoyant force is the main extra force on the jet flow in the acceleration process, the superimposing model predicted the maximum velocity decay with precise accuracy in a Reynolds number range of 667-4000, based on slot heights of 20 and 30 mm and slot velocities of 0.50, 1.00 and 2.00 m/s. At a distance of 1000 mm from the slot, the velocity profile displays a self similarity character like an isothermal turbulent jet. In the final region, where the buoyancy flux completely dominates the jet, the jet behaved like a plume with an unstable flow field.

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“…It should be noted that projecting the flammability factor downstream to low values (e.g., 0.01) will likely assume the dominance of momentum mixing beyond the momentum length scale, z b (~600 mm in this case) where buoyancy becomes nontrivial. Studies of buoyant axisymmetric jets show mixing is greatly enhanced for both the mean and secondorder moments (Papanicolaou and List 1988;So and Aksoy 1993). Therefore, assuming momentum dominance in the far downstream will result in a conservative, overprediction of flammability.…”

Section: Predicting Ignitabilitymentioning

confidence: 96%

Statistically advanced, self-similar, radial probability density functions of atmospheric and under-expanded hydrogen jets

Ruggles

2015

Exp Fluids

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used to separate the turbulent and pure air data, and thusly estimate intermittency. Beta-distributions (four parameters) are used to accurately represent the turbulent distribution moments. This combination of measured intermittency and four-parameter beta-distributions constitutes a new, simple approach to model scalar mixing. Comparisons between global moments from the data and moments calculated using the proposed model show excellent agreement. This was attributed to the high quality of the measurements which reduced the width of the correctly identified, noiseaffected pure air distribution, with respect to the turbulent mixing distribution. The ignitability of the atmospheric jet is determined using the flammability factor calculated from both kernel density estimated (KDE) PDFs and PDFs generated using the newly proposed model. Agreement between contours from both approaches is excellent. Ignitability of the under-expanded jet is also calculated using KDE PDFs. Contours are compared with those calculated by applying the atmospheric model to the under-expanded jet. Once again, agreement is excellent. This work demonstrates that self-similar scalar mixing statistics and ignitability of atmospheric jets can be accurately described by the proposed model. This description can be applied with confidence to under-expanded jets, which are more realistic of leak and fuel injection scenarios.Abstract This paper presents improved statistical insight regarding the self-similar scalar mixing process of atmospheric hydrogen jets and the downstream region of underexpanded hydrogen jets. Quantitative planar laser Rayleigh scattering imaging is used to probe both jets. The self-similarity of statistical moments up to the sixth order (beyond the literature established second order) is documented in both cases. This is achieved using a novel self-similar normalization method that facilitated a degree of statistical convergence that is typically limited to continuous, pointbased measurements. This demonstrates that image-based measurements of a limited number of samples can be used for self-similar scalar mixing studies. Both jets exhibit the same radial trends of these moments demonstrating that advanced atmospheric self-similarity can be applied in the analysis of under-expanded jets. Self-similar histograms away from the centerline are shown to be the combination of two distributions. The first is attributed to turbulent mixing. The second, a symmetric Poisson-type distribution centered on zero mass fraction, progressively becomes the dominant and eventually sole distribution at the edge of the jet. This distribution is attributed to shot noise-affected pure air measurements, rather than a diffusive superlayer at the jet boundary. This conclusion is reached after a rigorous measurement uncertainty analysis and inspection of pure air data collected with each hydrogen data set. A threshold based upon the measurement noise analysis is

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On vertical turbulent buoyant jets

Cited by 20 publications

References 22 publications

Comparison of Combustion Models for Lifted Hydrogen Flames within RANS Framework

Comparison of Combustion Models for Lifted Hydrogen Flames within RANS Framework

Experimental investigation and modelling of a buoyant attached plane jet in a room

Statistically advanced, self-similar, radial probability density functions of atmospheric and under-expanded hydrogen jets

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