scholarly journals Sound generation by turbulent premixed flames

2018 ◽  
Vol 843 ◽  
pp. 29-52 ◽  
Author(s):  
Ali Haghiri ◽  
Mohsen Talei ◽  
Michael J. Brear ◽  
Evatt R. Hawkes
Keyword(s):  
Numerical Study ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Computational Cost ◽  
Turbulent Flames ◽  
Far Field ◽  
Turbulent Premixed Flames ◽  
Acoustic Sources ◽  
Field Sound ◽  
Turbulent Premixed

This paper presents a numerical study of the sound generated by turbulent, premixed flames. Direct numerical simulations (DNS) of two round jet flames with equivalence ratios of 0.7 and 1.0 are first carried out. Single-step chemistry is employed to reduce the computational cost, and care is taken to resolve both the near and far fields and to avoid noise reflections at the outflow boundaries. Several significant features of these two flames are noted. These include the monopolar nature of the sound from both flames, the stoichiometric flame being significantly louder than the lean flame, the observed frequency of peak acoustic spectral amplitude being consistent with prior experimental studies and the importance of so-called ‘flame annihilation’ events as acoustic sources. A simple model that relates these observed annihilation events to the far-field sound is then proposed, demonstrating a surprisingly high degree of correlation with the far-field sound from the DNS. This model is consistent with earlier works that view a premixed turbulent flame as a distribution of acoustic sources, and provides a physical explanation for the well-known monopolar content of the sound radiated by premixed turbulent flames.

Structure and propagation speeds of turbulent premixed flames—A numerical study

1991 ◽  
Vol 83 (1-2) ◽  
pp. 155-173 ◽  
Author(s):  
Sherif H. El Tahry ◽  
Christopher Rutland ◽  
Joel Ferziger
Keyword(s):  
Numerical Study ◽  
Premixed Flames ◽  
Turbulent Premixed Flames ◽  
Turbulent Premixed

Sound emission from open turbulent premixed flames

1968 ◽  
Vol 303 (1475) ◽  
pp. 409-427 ◽  
Keyword(s):  
Premixed Flames ◽  
Turbulent Flames ◽  
Rate Of Change ◽  
Gas Mixture ◽  
Turbulent Premixed Flames ◽  
Combustible Gas ◽  
Rate Of Increase ◽  
Radiated Sound ◽  
Combustible Gas Mixture ◽  
Turbulent Premixed

A study of the noise produced by turbulent premixed flames stabilized on open burners is described. It is shown that such flames may be represented acoustically as a collection of monopole sound sources in the combustion zone. The radiated sound pressure is dependent on the rate of change of the rate of increase of volume of the gas during combustion, which varies owing to the turbulence in the flow. The rate of volume increase is proportional to the rate of consumption of combustible gas mixture in the flame. To measure this quantity, an optical technique has been developed which relies on observations of changes in the intensity of emission from the free radicals C 2 or CH generated in the reaction zone. Good quantitative agreement is obtained between the radiated sound pressures calculated from these intensity measurements and the values recorded simultaneously with a microphone. A correlation observed between the mean emission intensities of C 2 and CH radicals and the total flow rate of combustible gas mixture both in the laminar and turbulent flames, and in their transition region, supports the wrinkled laminar flame concept of turbulent flame propagation.

An Analysis of Local Quantities of Turbulent Premixed Flames Using DNS Databases

2007 ◽  
Author(s):  
Kazuya Tsuboi ◽  
Shinnosuke Nishiki ◽  
Tatsuya Hasegawa
Keyword(s):  
Reaction Rate ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Three Dimensional ◽  
Flame Surface ◽  
Turbulent Premixed Flames ◽  
Density Ratios ◽  
Turbulent Burning Velocity ◽  
Turbulent Premixed

An analysis of local flame area was performed using DNS (Direct Numerical Simulation) databases of turbulent premixed flames with different density ratios and with different Lewis numbers. Firstly, a local flame surface at a prescribed progress variable was identified as a local three-dimensional polygon. And then the polygon was divided into some triangles and local flame area was evaluated. The turbulent burning velocity was evaluated using the ratio of the area of turbulent flame to that of planar flame and compared with the turbulent burning velocity obtained by the reaction rate.

scholarly journals Effects of pressure gradients on turbulent premixed flames

1997 ◽  
Vol 353 ◽  
pp. 83-114 ◽  
Author(s):  
DENIS VEYNANTE ◽  
THIERRY POINSOT
Keyword(s):  
Pressure Gradient ◽  
Turbulent Transport ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Flame Speed ◽  
Pressure Gradients ◽  
Turbulent Premixed Flames ◽  
Turbulent Flame Speed ◽  
Flame Brush ◽  
Turbulent Premixed

In most practical situations, turbulent premixed flames are ducted and, accordingly, subjected to externally imposed pressure gradients. These pressure gradients may induce strong modifications of the turbulent flame structure because of buoyancy effects between heavy cold fresh and light hot burnt gases. In the present work, the influence of a constant acceleration, inducing large pressure gradients, on a premixed turbulent flame is studied using direct numerical simulations.A favourable pressure gradient, i.e. a pressure decrease from unburnt to burnt gases, is found to decrease the flame wrinkling, the flame brush thickness, and the turbulent flame speed. It also promotes counter-gradient turbulent transport. On the other hand, adverse pressure gradients tend to increase the flame brush thickness and turbulent flame speed, and promote classical gradient turbulent transport. As proposed by Libby (1989), the turbulent flame speed is modified by a buoyancy term linearly dependent on both the imposed pressure gradient and the integral length scale lt.A simple model for the turbulent flux u″c″ is also proposed, validated from simulation data and compared to existing models. It is shown that turbulent premixed flames can exhibit both gradient and counter-gradient transport and a criterion integrating the effects of pressure gradients is derived to differentiate between these regimes. In fact, counter-gradient diffusion may occur in most practical ducted flames.

scholarly journals Modelling of Conditional Scalar Dissipation Rate in Turbulent Premixed Combustion

Computation ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 26 ◽  
Author(s):  
Shokri Amzin ◽  
Mariusz Domagała
Keyword(s):  
Dissipation Rate ◽  
Premixed Flames ◽  
Moment Closure ◽  
Navier Stokes ◽  
Scalar Dissipation ◽  
Flame Surface ◽  
Scalar Dissipation Rate ◽  
Turbulent Premixed Flames ◽  
Conditional Moment ◽  
Turbulent Premixed

In turbulent premixed flames, for the mixing at a molecular level of reactants and products on the flame surface, it is crucial to sustain the combustion. This mixing phenomenon is featured by the scalar dissipation rate, which may be broadly defined as the rate of micro-mixing at small scales. This term, which appears in many turbulent combustion methods, includes the Conditional Moment Closure (CMC) and the Probability Density Function (PDF), requires an accurate model. In this study, a mathematical closure for the conditional mean scalar dissipation rate, <Nc|ζ>, in Reynolds, Averaged Navier–Stokes (RANS) context is proposed and tested against two different Direct Numerical Simulation (DNS) databases having different thermochemical and turbulence conditions. These databases consist of lean turbulent premixed V-flames of the CH4-air mixture and stoichiometric turbulent premixed flames of H2-air. The mathematical model has successfully predicted the peak and the typical profile of <Nc|ζ> with the sample space ζ and its prediction was consistent with an earlier study.

Sign in / Sign up

Export Citation Format

Share Document