Evolution of turbulence through a broadened preheat zone in a premixed piloted Bunsen flame from conditionally-averaged velocity measurements

Wabel, Timothy M.; Skiba, A.; Driscoll, James F.

doi:10.1016/j.combustflame.2017.09.013

Cited by 52 publications

(15 citation statements)

References 47 publications

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“…By contrast, in cases E and F, ̃ decays monotonically from the unburned gas side of the flame brush due to the reduction of forcing and viscous dissipation. Thus, the disappearance of small-scale eddies due to the decay of turbulence and higher kinematic viscosity 70 in the burned gases is responsible for the weakened role of 11, ( ) components conditioned on products. and B, which is followed by the magnitudes of the , and components.…”

Section: Please Cite This Article Asmentioning

confidence: 99%

Statistical behaviors of conditioned two-point second-order structure functions in turbulent premixed flames in different combustion regimes

et al. 2019

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The second-order structure functions and their components conditioned upon various events have been analysed for un-weighted and density-weighted velocities using a Direct Numerical Simulation (DNS) database. The heat release due to combustion has been shown to have significant influences on the structure functions and their components conditioned on different mixture states. The use of densityweighted velocities changes the relative magnitudes of differently conditioned structure functions but does not reduce the scatter of these magnitudes. The structure functions conditioned to constant-density unburned reactants at both points and normalized using the root-mean-square velocity conditioned to the reactants are larger at higher values of mean reaction progress variables ̅ (deeper within the flame brush), with this trend being not weakened with increasing turbulence intensity ′⁄. These results indicate that, contrary to a common belief, combustion-induced thermal expansion can significantly affect the incoming constant-density turbulent flow of unburned reactants even at ′⁄ and Karlovitz number as large as 10 and 18, respectively. The statistical behaviours of the structure functions reveal that the magnitude of the flame normal gradient of the velocity component tangential to the local flames can be significant and it increases with increasing turbulence intensity. Moreover, the structure functions conditioned on both points in the heat release zone bear the signature of the anisotropic effects induced by baroclinic torque for the flames belonging to the wrinkled flamelets and corrugated flamelets regimes. These anisotropic effects weaken with increasing turbulence intensity in the thin reaction zones regime.

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Section: Please Cite This Article Asmentioning

confidence: 99%

Statistical behaviors of conditioned two-point second-order structure functions in turbulent premixed flames in different combustion regimes

et al. 2019

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“…Since an increase in burning rate due to flame-generated turbulence was hypothesized by Karlovitz et al [1] and Scurlock and Grover [2], the influence of combustion-induced density variations on turbulent flow within a premixed flame brush was studied in a number of papers reviewed elsewhere [3][4][5][6], see also recent Refs. [7][8][9][10][11]. The majority of such studies addressed the first and second moments of velocity field within mean flame brush, with the moments being averaged in the conventional way by allowing for contributions from unburned reactants, intermediate mixture states, and combustion products simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Application of conditioned structure functions to exploring influence of premixed combustion on two-point turbulence statistics

Sabelnikov

Lipatnikov

Nishiki

et al. 2019

Proceedings of the Combustion Institute

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Colloquium: Turbulent flames Total length: 6181 words  Main text: 3918 words  Equations: (8 lines + 8 blank lines) (7.6 words/line) = 122 words  References: (53+2) (2.3 lines/reference) (7.6 words/line) = 961 words  Figure 1: (154 mm + 10 mm) (2.2 words/mm) + 109 words = 470 words  Figure 2: (47 mm + 10 mm) (2.2 words/mm) + 14 words = 139 words  Figure 3: (101 mm + 10 mm) (2.2 words/mm) + 55 words = 297 words  Figure 4: (101 mm + 10 mm) (2.2 words/mm) + 28 words = 272 wordsWe agree to pay charges for color publications if color printing is deemed necessary. AbstractIn order to investigate the influence of combustion-induced thermal expansion on turbulent flow within a premixed flame brush, a new method is introduced. The method consists in analyzing structure functions of the velocity field, which characterize velocity difference in two points A and B, with the structure functions being conditioned to various events; (i) unburned reactants in both points, (ii) combustion products in both points, (iii) intermediate states of the mixture in both points, (iv) the reactants in one point and the products in another point, (v) the reactants in one point and an intermediate state in another point, and (vi) the products in one point and an intermediate state in another point. Such structure functions and relevant probabilities are defined in the paper. Subsequently, the structure functions and the probabilities are extracted from Direct Numerical Simulation (DNS) data obtained from two statistically planar, 1D, fully-developed, weakly turbulent, premixed flames characterized by two significantly different (7.52 and 2.50) density ratios, with all other things being approximately equal. Obtained results indicate that (i) the conditioned structure functions differ significantly from the mean structure functions and (ii) the newly introduced approach could convey information important for understanding fundamentals of flame-turbulence interaction and finding issues that require further research. In particular, application of the approach to the aforementioned DNS data shows that the combustion-induced thermal expansion substantially affects smallscale two-point velocity statistics in the incoming constant-density turbulent flow of unburned reactants within a premixed flame brush.

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“…Since a direct comparison with experimental data has not been possible due to the lack of public consistent measurements, radial profiles of and related fluctuations at different distances from the nozzle exit are qualitatively compared to the previous experimental results [13] of a similar configuration. Figure 2a shows the radial profiles of .…”

Section: Resultsmentioning

confidence: 99%

“…The influence of the co-flow is left to future work, but there is the hypothesis that it could be entrained by large eddies at the nozzle outlet, modifying the composition of the mixture. This question has been addressed in [13]. The radial jets account for the 6% of the total mass flow rate.…”

Section: Configuration and Test Case Descriptionmentioning

confidence: 99%

Study on coherent structures for high turbulence burner

Ceschin

Angelilli

Pérez

et al. 2021

AIAA Scitech 2021 Forum

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A numerical study on the coherent structure generation and analysis by means of and 2 criteria is conducted. The case under study is represented by the HiPilot burner, experimentally investigated at the University of Michigan for the classification of turbulent premixed flames based on Karlovitz number. Large eddy simulations of a cold jet are performed to gain insights into the dynamics and characteristics of the high Reynolds number turbulent flow, especially in the section that is optically inaccessible for measurements.

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Evolution of turbulence through a broadened preheat zone in a premixed piloted Bunsen flame from conditionally-averaged velocity measurements

Cited by 52 publications

References 47 publications

Statistical behaviors of conditioned two-point second-order structure functions in turbulent premixed flames in different combustion regimes

Statistical behaviors of conditioned two-point second-order structure functions in turbulent premixed flames in different combustion regimes

Application of conditioned structure functions to exploring influence of premixed combustion on two-point turbulence statistics

Study on coherent structures for high turbulence burner

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