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Thierry Schuller - One of the best experts on this subject based on the ideXlab platform.
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analysis of chemiluminescence density and Heat Release Rate fluctuations in acoustically perturbed laminar premixed flames
Combustion and Flame, 2015Co-Authors: Daniel Durox, Franck Richecoeur, Thierry SchullerAbstract:Abstract Laser interferometric vibrometry (LIV) has recently been proposed as an alternative mean to obtain time-resolved density and Heat Release Rate measurements at relatively low cost and experimental effort. This technique is sensitive to fluctuations of the refractive index of gases resulting from density and composition changes along the laser beam intersecting the reacting flow. It yields a line-of-sight integRated signal of the probed flow from which density and Heat Release Rate disturbances may be inferred. The link between these signals with chemiluminescence is examined in the present study by first considering a theoretical analysis to determine the relationships between the LIV, density and Heat Release Rate perturbation signals in a multi-species reactive mixture of gases. For air combustion systems interacting with sound waves, low frequency density perturbations in the flame zone, result mainly from Heat Release Rate fluctuations below a certain frequency threshold. An experimental analysis is then conducted with confined conical laminar premixed flames submitted to harmonic flow modulations. Measurements are presented for methane–air mixtures at different equivalence ratios 0.8 ≤ ϕ ≤ 1.2 and thermal powers. It is shown that fluctuations of the chemiluminescence signal examined in different wavelength bands, including the OH * , CH * or the entire visible emission bands, always capture the same dynamics. This indicates that Heat Release Rate fluctuations can be deduced without specific filters for the laminar premixed methane–air flames investigated. It is then shown that Heat Release Rate measurements deduced from LIV and chemiluminescence data match well. A proportional relation is found that does not depend on the measurement position, modulation frequency and modulation level for fixed injection conditions. This linear relation slightly depends on the mean flow operating conditions partly due to the difficulty to interpret chemiluminescence emission for rich flames.
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Reconstruction of Heat Release Rate disturbances based on transmission of ultrasounds: Experiments and modeling for perturbed flames
Combustion and Flame, 2013Co-Authors: Franck Richecoeur, Thierry SchullerAbstract:Heat Release Rate fluctuations cause recurrent problems in many steady operating combustors. Direct measurements are difficult and these fluctuations are generally inferred from optical diagnostics. An alternative acoustic method was recently developed and is validated here in the case of unconfined laminar premixed flames submitted to harmonic flow modulations. The technique relies on determining the transmission time of frequency-modulated ultrasounds propagating through the perturbed flow. The transmission of ultrasounds is altered by the perturbed interface between the burned gases and ambient air and by the perturbed flame front. A theoretical link between the dynamics of these two interfaces is derived for small low frequency perturbations. The predicted shapes taken by these interfaces are compared with two-color Schlieren images. This model is then used to determine the resulting Heat Release Rate fluctuations and corresponding disturbances in the transmission time of ultrasounds. An analytical expression is derived for the transfer function between Heat Release Rate and sound transmission time disturbances as a function of frequency when these conical flames are submitted to harmonic flow disturbances. Measurements made with this acoustic technique are compared to analytical predictions and to optical measurements exploiting the chemiluminescence emission from the flame. Effects of the forcing frequency and modulation level are examined. Results indicate a good match between predictions and measurements for the gain and phase of the transfer functions of the lean and stoichiometric unconfined flames investigated when the input level is not too large. Issues and perspectives are then briefly discussed to extend this Heat Release Rate measurement technique to practical configurations.
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interferometric determination of Heat Release Rate in a pulsated flame
Combustion and Flame, 2013Co-Authors: Thomas Leitgeb, Daniel Durox, Thierry Schuller, Fabrice Giuliani, Stefan Koberl, Jakob WoisetschlagerAbstract:Abstract Introducing a new measurand, namely the Rate of change of density in line-of-sight, can be of great interest for people working on thermoacoustics and combustion noise. In this work the relationship between the radiated acoustic pressure, the time Rate of change of unsteady Heat Release and of density fluctuations in a laminar pulsated premixed flame is presented. The burner produced a ‘M’-shaped flame which is excited by harmonic modulations of the flow at two forcing frequencies f = 51 and 101 Hz. Measurements were performed by a microphone to record the sound pressure radiated by the flame in the far field, a photomultiplier to collect the light emission from which the Heat Release Rate was estimated, and a laser vibrometer to detect the Rate of change of density fluctuations within the reaction region. As the latter technique is a novel approach in combustion analysis a detailed description of the fundamentals of laser interferometric vibrometry is presented. Laser vibrometry offers the advantage to be low-demanding in terms of instrumentation and settings and to be relatively straightforward to process for a broad frequency range. The different signals recorded are correlated. An interpretation of the measurement data is given and the potential of laser vibrometry to obtain time resolved data on density and Heat Release Rate fluctuations in the flame region is demonstRated.
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Determination of Heat Release Rate Disturbances in Unconfined Flames Based on Fluctuations in the Travel Time of Ultrasonic Waves
Combustion Science and Technology, 2012Co-Authors: Franck Richecoeur, Thierry SchullerAbstract:The article presents a new method to measure Heat Release Rate disturbances from flames when optical access is limited. The technique is based on the determination of the travel time of ultrasonic waves propagating through the flow. The link between Heat Release Rate and sound travel time disturbances depends on the configuration considered. An expression is established here for the case of unconfined premixed flames driven by buoyancy forces associated with the Kelvin-Helmholtz instability formed by the interaction between accelerating hot burned gases and cold ambient air at rest. The system and the principle used for the determination of the sound travel time are then presented and validated under nonreacting conditions. Effects of the main parameters on the precision of this detection technique are examined experimentally. Measurements in reacting conditions are compared to Heat Release Rate data obtained with another technique based on the chemiluminescence emission. A good agreement is obtained between both signals for the different cases explored demonstrating the sensitivity of the proposed technique.
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Development of an acoustic diagnostic for determination of Heat Release Rate perturbations in pulsated flames
Mécanique & Industries, 2011Co-Authors: Franck Richecoeur, Thierry SchullerAbstract:Heat Release Rate fluctuations are the source of combustion instabilities that cause recurrent problems in many combustors. These quantities are difficult to measure and optical techniques are generally implemented. The initial validation of an alternative method is presented in the case of pulsated laminar premixed flames. The technique relies on determining the travel time of ultrasonic waves propagating through the flow. The link between Heat Release Rate fluctuations and perturbations in the travel time of ultrasonic waves is established. Measurements made with this method are compared with optical measurements and an analytical model. A good agreement is obtained for the gain and phase of the transfer function between perturbations in the sound travel time and Heat Release Rate disturbances when the flame is submitted to harmonic modulations of the flow. This work validates the principle of the proposed technique and lays the foundations for future developments.
Nedunchezhian Swaminathan - One of the best experts on this subject based on the ideXlab platform.
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Heat Release Rate estimation in laminar premixed flames using laser induced fluorescence of ch2o and h atom
Combustion and Flame, 2016Co-Authors: Irfan A Mulla, Nedunchezhian Swaminathan, A Dowlut, Taaha Hussain, Zacharias M Nikolaou, S R Chakravarthy, R. BalachandranAbstract:The present work demonstRates the feasibility of Heat Release Rate imaging using the laser-induced fluorescence (LIF) of atomic hydrogen (H-atom) and formaldehyde (CH2O) in laminar premixed flames. The product of H-atom LIF and CH2O LIF signals is evaluated on a pixel-by-pixel basis and is compared with that of the OH × CH2O technique. These results for equivalence ratio ranging from 0.8 to 1.1 are compared with computations of one-dimensional freely-propagating flames. The performance of these markers is studied based on the following two aspects: the spatial accuracy of the local Heat Release Rate and the trend in the total Heat Release Rate with equivalence ratio. The measured trend in the spatial distribution of radicals and the deduced Heat Release Rate agree well with the computational values. The variation in the spatially integRated Heat Release Rate as a function of equivalence ratio is also investigated. The results suggest that the trend in the variation of the integRated Heat Release Rate and the spatial location of Heat Release Rate can be evaluated by either of these markers. The OH-based marker showed certain sensitivity to the chemical mechanism as compared to the H-atom based marker. Both the OH-based and H-atom based techniques provide close estimates of Heat Release Rate. The OH based technique has practical advantage when compared to the H-atom based method, primarily due to the fact that the H-atom LIF is a two-photon process.
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Heat Release Rate markers for premixed combustion
Combustion and Flame, 2014Co-Authors: Zacharias M Nikolaou, Nedunchezhian SwaminathanAbstract:Abstract The validity of the commonly used flame marker for Heat Release Rate (HRR) visualization, namely the Rate of the reaction OH + CH 2 O ⇔ HCO + H 2 O is re-examined. This is done both for methane–air and multi-component fuel–air mixtures for lean and stoichiometric conditions. Two different methods are used to identify HRR correlations, and it is found that HRR correlations vary strongly with stoichiometry. For the methane mixture there exist alternative HRR markers, while for the multi-component fuel flame the above correlation is found to be inadequate. Alternative markers for the HRR visualization are thus proposed and their performance under turbulent conditions is evaluated using DNS data.
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Heat Release Rate correlation and combustion noise in premixed flames
Journal of Fluid Mechanics, 2011Co-Authors: Nedunchezhian Swaminathan, Ann P. Dowling, R. BalachandranAbstract:The sound emission from open turbulent flames is dictated by the two-point spatial correlation of the Rate of change of the fluctuating Heat Release Rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating Heat Release Rate is deduced to be about tau(c)/34 on an average, where tau(c) is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction Rate obtained from Reynolds-averaged Navier-Stokes (RANS) calculations of open turbulent premixed flames employing the standard (k) over tilde-(epsilon) over tilde model and an algebraic reaction Rate closure, involving a recently developed scalar dissipation Rate model, are used to obtain the far-field sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and Heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of Heat Release Rate is low.
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On the correlation of Heat Release Rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2011Co-Authors: Nedunchezhian Swaminathan, R. Balachandran, Ann P. DowlingAbstract:Abstract Two-point spatial correlation of Rate of change of fluctuating Heat Release Rate dictates the sound emission from open turbulent flames and this correlation is not directly addressed in past studies. The results from Direct Numerical Simulation and laser diagnostics of turbulent premixed flames are analyzed to study this correlation function and the two-point spatial correlation of the fluctuating Heat Release Rate. The analyses showed that these correlation functions can be represented very well using Gaussian functions. The integral length scale, l , for the fluctuating Heat Release Rate is about one to two planar laminar flame thermal thickness, δ L o , and this is not influenced by turbulence Reynolds number and swirl. The length scale for the Rate of change of fluctuating Heat Release Rate is about δ L o / 4 . The far field sound pressure levels of open turbulent premixed flames calculated by post processing RANS simulation results along with the above length scales compare very well with measured values.
Wan Ki Chow - One of the best experts on this subject based on the ideXlab platform.
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improved model for estimating sidewall effect on the fire Heat Release Rate of horizontal cable tray
Process Safety and Environmental Protection, 2021Co-Authors: Xianjia Huang, He Zhu, Lan Peng, Chihonn Cheng, Wan Ki ChowAbstract:Abstract The occurrence Rate of fire events involved with cables is high and a fire hazard analysis is needed. A cable tray may be commonly placed on a wall. The fire hazards of multiple cable trays are affected by the supporting wall to give a higher maximum Heat Release Rate. Taking the wall constraint effect on cable burning into account, a new model for the fire Heat Release Rate of a cable tray fire against a sidewall is developed based on small scale (cone calorimeter) measurements. The newly developed model introduces a constant m to reflect the acceleration in cable burning due to the sidewall. With a properly chosen value of m, the results obtained using the newly developed model agree well with the experimental data. The error in the peak fire Heat Release Rate value is considerably smaller than those of other models. This work improves the understanding of the fire risk of a cable tray with a sidewall.
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A discussion on estimating the Heat Release Rate of design fires in Hong Kong
Journal of Applied Fire Science, 2012Co-Authors: Wan Ki ChowAbstract:Many big construction projects in Hong Kong have difficulties to comply with prescriptive fire codes. Fire safety provisions have to go through Fire Engineering Approach (FEA) or performance-based design (PBD). The Heat Release Rate of a design fire is the most important parameter in fire safety assessment. However, a very low design fire less than 5 MW is usually assumed, even in large crowded spaces, such as public transport terminals and shopping malls. Surveys indicated that local buildings usually store combustibles exceeding the upper limit imposed by the codes. A post-flashover fire due to whatever reason would give even higher Heat Release Rate. As data for local combustible products is not yet available, Heat Release Rate in most of the FEA/PBD projects were estimated by crude methods not supported by full-scale burning tests. Three methods commonly adopted to estimate the Heat Release Rate will be discussed in this article. Some calculations were even wrong in taking average Heat Release Rate as the peak Heat Release Rate. Correct calculation on Heat Release Rate by burning combustibles is necessary with support of full-scale burning tests.Department of Building Services Engineerin
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Heat Release Rate of accidental fire in a supertall building residential flat
Building and Environment, 2010Co-Authors: Cheuk Lun Chow, Wan Ki ChowAbstract:Abstract Residential highrise building fire of height above 200 m is now a concern in the Far East. Long-term survey study on fire load density indicated that high amount of combustibles over the local upper limit of 1135 M Jm −2 used to be stored in residential flats. Wind-induced air-flow Rates through openings at upper levels of those tall buildings can be very high. Stack effect in areas with large indoor and outdoor temperature differences (such as 14 °C indoor and − 30 °C outdoor at Harbin, Heilongjiang, China) will also give high ventilation Rate through leakage areas. Adequate oxygen is then supplied to burn up all stored combustibles to give a big fire. In applying performance-based design to determine the fire safety provisions, Heat Release Rate of the design fire is the first parameter to decide. In this paper, stack effect and wind action on possible increase in the Heat Release Rate for fires in supertall residential buildings will be explored. Air intake Rates through openings to rooms at high levels due to stack effect and wind action are estimated by simple empirical formula. The maximum Heat Release Rates for well-developed room fires in these tall buildings under different stack and wind conditions are determined by varying two parameters. Air flow Rate through openings in an 800 m tall building induced by wind gust can be over 20 times the value at ground level. Consequently, Heat Release Rate can be much higher, confirming experimental studies on building fires under wind action.
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Fuel Load and Peak Heat Release Rate Correlations in Post-Flashover Room Fires
Heat Transfer Engineering, 2010Co-Authors: Wan Ki ChowAbstract:Flashover might occur rapidly as a consequence of non-accidental building fires. Response of the stored combustible items (being ignited and burned) should be studied carefully in such developed fires, which are ventilation-controlled. Air supply Rate and Heat fluxes acting at the materials would affect burning of the combustibles. A wide range of peak Heat Release Rates with different fire durations results under different Heat fluxes. The amount of combustibles denoted by fire or fuel load commonly adopted to quantify fire risks is no longer the key point in generating the Heat Release Rate. A room with a large fire load may not give high Heat Release Rates if the air supply is inadequate, or if the radiant Heat flux is low. In this article, correlation of the peak Heat Release Rate in burning the material under flashover with the fire load of the combustibles with adequate ventilation will be investigated. Data compiled from full-scale burning tests on well-developed room fires with steady burning are ...
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Scale modeling on the effect of air velocity on Heat Release Rate in tunnel fire
Journal of Applied Fire Science, 2008Co-Authors: C. Chen, Y. X. Yang, G. Q. Kang, Wan Ki ChowAbstract:There are concerns that the air supply Rate would increase in a tunnel with a moving train. Higher relative air velocity between the train wall and air caused by piston effect would then give higher burning Rates in a tunnel fire. In this article, the effect of air velocity on Heat Release Rate in a subway fire was studied in a scale model tunnel. Heptane was used as the fuel. Results showed that increasing the air velocity to fire would increase the Heat Release Rate. This point should be considered in designing fire safety management schemes in subways when the train is moving in tunnels.Department of Building Services Engineerin
R. Balachandran - One of the best experts on this subject based on the ideXlab platform.
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Heat Release Rate estimation in laminar premixed flames using laser induced fluorescence of ch2o and h atom
Combustion and Flame, 2016Co-Authors: Irfan A Mulla, Nedunchezhian Swaminathan, A Dowlut, Taaha Hussain, Zacharias M Nikolaou, S R Chakravarthy, R. BalachandranAbstract:The present work demonstRates the feasibility of Heat Release Rate imaging using the laser-induced fluorescence (LIF) of atomic hydrogen (H-atom) and formaldehyde (CH2O) in laminar premixed flames. The product of H-atom LIF and CH2O LIF signals is evaluated on a pixel-by-pixel basis and is compared with that of the OH × CH2O technique. These results for equivalence ratio ranging from 0.8 to 1.1 are compared with computations of one-dimensional freely-propagating flames. The performance of these markers is studied based on the following two aspects: the spatial accuracy of the local Heat Release Rate and the trend in the total Heat Release Rate with equivalence ratio. The measured trend in the spatial distribution of radicals and the deduced Heat Release Rate agree well with the computational values. The variation in the spatially integRated Heat Release Rate as a function of equivalence ratio is also investigated. The results suggest that the trend in the variation of the integRated Heat Release Rate and the spatial location of Heat Release Rate can be evaluated by either of these markers. The OH-based marker showed certain sensitivity to the chemical mechanism as compared to the H-atom based marker. Both the OH-based and H-atom based techniques provide close estimates of Heat Release Rate. The OH based technique has practical advantage when compared to the H-atom based method, primarily due to the fact that the H-atom LIF is a two-photon process.
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Heat Release Rate correlation and combustion noise in premixed flames
Journal of Fluid Mechanics, 2011Co-Authors: Nedunchezhian Swaminathan, Ann P. Dowling, R. BalachandranAbstract:The sound emission from open turbulent flames is dictated by the two-point spatial correlation of the Rate of change of the fluctuating Heat Release Rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating Heat Release Rate is deduced to be about tau(c)/34 on an average, where tau(c) is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction Rate obtained from Reynolds-averaged Navier-Stokes (RANS) calculations of open turbulent premixed flames employing the standard (k) over tilde-(epsilon) over tilde model and an algebraic reaction Rate closure, involving a recently developed scalar dissipation Rate model, are used to obtain the far-field sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and Heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of Heat Release Rate is low.
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On the correlation of Heat Release Rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2011Co-Authors: Nedunchezhian Swaminathan, R. Balachandran, Ann P. DowlingAbstract:Abstract Two-point spatial correlation of Rate of change of fluctuating Heat Release Rate dictates the sound emission from open turbulent flames and this correlation is not directly addressed in past studies. The results from Direct Numerical Simulation and laser diagnostics of turbulent premixed flames are analyzed to study this correlation function and the two-point spatial correlation of the fluctuating Heat Release Rate. The analyses showed that these correlation functions can be represented very well using Gaussian functions. The integral length scale, l , for the fluctuating Heat Release Rate is about one to two planar laminar flame thermal thickness, δ L o , and this is not influenced by turbulence Reynolds number and swirl. The length scale for the Rate of change of fluctuating Heat Release Rate is about δ L o / 4 . The far field sound pressure levels of open turbulent premixed flames calculated by post processing RANS simulation results along with the above length scales compare very well with measured values.
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Heat Release Rate measurement in turbulent flames
2005Co-Authors: B.o. Ayoola, R. Balachandran, Epaminondas Mastorakos, Clemens F. KaminskiAbstract:The dominant industrial approach for the reduction of NO x emissions in industrial gas turbines is the lean pre-mixed prevaporized concept. The main advantage of this concept is the lean operation of the combustion process; this decreases the Heat Release Rate from the flame and results in a reduction in operating temperature. The direct measurement of Heat Release Rates via simultaneous laser induced fluorescence of OH and CH 2O radicals using planar laser induced fluorescence. The product of the two images correlated with the forward production Rate of the HCO radical, which in turn has correlated well with Heat Release Rates from premixed hydrocarbon flames. The experimental methodology of the measurement of Heat Release Rate and applications in different turbulent premixed flames were presented. This is an abstract of a paper presented at the 7th World Congress of Chemical Engineering (Glasgow, Scotland 7/10-14/2005).
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Spatially resolved Heat Release Rate measurements in turbulent premixed flames
Combustion and Flame, 2005Co-Authors: B.o. Ayoola, R. Balachandran, Jonathan H. Frank, Epaminondas Mastorakos, Clemens F. KaminskiAbstract:Heat Release Rate is a fundamental property of great importance for the theoretical and experimental elucidation of unsteady flame behaviors such as combustion noise, combustion instabilities, and pulsed combustion. Investigations of such thermoacoustic interactions require a reliable indicator of Heat Release Rate capable of resolving spatial structures in turbulent flames. Traditionally, Heat Release Rate has been estimated via OH or CH radical chemiluminescence; however, chemiluminescence suffers from being a line-of-sight technique with limited capability for resolving small-scale structures. In this paper, we report spatially resolved two-dimensional measurements of a quantity closely related to Heat Release Rate. The diagnostic technique uses simultaneous OH and CH2O planar laser-induced fluorescence (PLIF), and the pixel-by-pixel product of the OH and CH2O PLIF signals has previously been shown to correlate well with local Heat Release Rates. Results from this diagnostic technique, which we refer to as Heat Release Rate imaging (HR imaging), are compared with traditional OH chemiluminescence measurements in several flames. Studies were performed in lean premixed ethylene flames stabilized between opposed jets and with a bluff body. Correlations between bulk strain Rates and local Heat Release Rates were obtained and the effects of curvature on Heat Release Rate were investigated. The results show that the Heat Release Rate tends to increase with increasing negative curvature for the flames investigated for which Lewis numbers are greater than unity. This correlation becomes more pronounced as the flame gets closer to global extinction.
Ann P. Dowling - One of the best experts on this subject based on the ideXlab platform.
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Heat Release Rate correlation and combustion noise in premixed flames
Journal of Fluid Mechanics, 2011Co-Authors: Nedunchezhian Swaminathan, Ann P. Dowling, R. BalachandranAbstract:The sound emission from open turbulent flames is dictated by the two-point spatial correlation of the Rate of change of the fluctuating Heat Release Rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating Heat Release Rate is deduced to be about tau(c)/34 on an average, where tau(c) is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction Rate obtained from Reynolds-averaged Navier-Stokes (RANS) calculations of open turbulent premixed flames employing the standard (k) over tilde-(epsilon) over tilde model and an algebraic reaction Rate closure, involving a recently developed scalar dissipation Rate model, are used to obtain the far-field sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and Heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of Heat Release Rate is low.
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On the correlation of Heat Release Rate in turbulent premixed flames
Proceedings of the Combustion Institute, 2011Co-Authors: Nedunchezhian Swaminathan, R. Balachandran, Ann P. DowlingAbstract:Abstract Two-point spatial correlation of Rate of change of fluctuating Heat Release Rate dictates the sound emission from open turbulent flames and this correlation is not directly addressed in past studies. The results from Direct Numerical Simulation and laser diagnostics of turbulent premixed flames are analyzed to study this correlation function and the two-point spatial correlation of the fluctuating Heat Release Rate. The analyses showed that these correlation functions can be represented very well using Gaussian functions. The integral length scale, l , for the fluctuating Heat Release Rate is about one to two planar laminar flame thermal thickness, δ L o , and this is not influenced by turbulence Reynolds number and swirl. The length scale for the Rate of change of fluctuating Heat Release Rate is about δ L o / 4 . The far field sound pressure levels of open turbulent premixed flames calculated by post processing RANS simulation results along with the above length scales compare very well with measured values.
