Direct numerical simulation of spray flame/acoustic interactions

Pera, Cécile; Réveillon, Julien

doi:10.1016/j.proci.2006.07.153

Cited by 15 publications

(7 citation statements)

References 10 publications

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“…In the case of a stationary flame, at a distance of 10 cm from the nozzle, Equation 4is observed to give a value of 0.8. This value is slightly higher than the one estimated in [14]; this discrepancy is probably due to the different definitions of Equation (4). Based on the Stokes number calculation, the dispersed phase is expected to follow the fluid.…”

Section: Characterisation Of Unsteady Spray Flamesmentioning

confidence: 62%

“…where l indicates the liquid phase. Equation 5defines the acoustic Stokes number (σ ac ) according to Pera and Reveillon [4]. At 200 Hz, σ l = 0.2 and the liquid is responsive to the acoustic perturbation and its dispersion is affected by the forcing frequency.…”

Section: Characterisation Of Unsteady Spray Flamesmentioning

confidence: 99%

“…They found the flame spectra to be similar to those in gaseous combustion, and this can be attributed to the small inertia of the droplets and to the consequently fast mixing. On the other hand, a stronger impact of the spray on the reaction rate, and so on the gain of the FTF, is observed in the case of laminar spray flames [4]. The important role played by turbulence was shown by Sujith [5], who presented an experimental investigation of the impact of acoustic waves on an air-atomised evaporating ethanol spray.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ethanol turbulent spray flame response to gas velocity modulation

Fratalocchi

Kok

2017

Combustion Theory and Modelling

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A numerical investigation of the interaction between a spray flame and an acoustic forcing of the velocity field is presented in this paper. In combustion systems, a thermoacoustic instability is the result of a process of coupling between oscillations in heat released and acoustic waves. When liquid fuels are used, the atomisation and the evaporation process also undergo the effects of such instabilities, and the computational fluid dynamics of these complex phenomena becomes a challenging task. In this paper, an acoustic perturbation is applied to the mass flow of the gas phase at the inlet and its effect on the evaporating fuel spray and on the flame front is investigated with unsteady Reynolds averaged Navier-Stokes numerical simulations. Two flames are simulated: a partially premixed ethanol/air spray flame and a premixed pre-vaporised ethanol/air flame, with and without acoustic forcing. The frequencies used to perturb the flames are 200 and 2500 Hz, which are representative for two different regimes. Those regimes are classified based on the Strouhal number St = (D/U)f f : at 200 Hz, St = 0.07, and at 2500 Hz, St = 0.8. The exposure of the flame to a 200 Hz signal results in a stretching of the flame which causes gas field fluctuations, a delay of the evaporation and an increase of the reaction rate. The coupling between the flame and the flow excitation is such that the flame breaks up periodically. At 2500 Hz, the evaporation rate increases but the response of the gas field is weak and the flame is more stable. The presence of droplets does not play a crucial role at 2500 Hz, as shown by a comparison of the discrete flame function in the case of spray and pre-vaporised flame. At low Strouhal number, the forced response of the pre-vaporised flame is much higher compared to that of the spray flame.

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Section: Characterisation Of Unsteady Spray Flamesmentioning

confidence: 62%

Section: Characterisation Of Unsteady Spray Flamesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ethanol turbulent spray flame response to gas velocity modulation

Fratalocchi

Kok

2017

Combustion Theory and Modelling

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“…More details may be found in [59,60,61]. A simple way to analyze flame interactions with a modulated acoustic field is to define a reduced frequency [60,62] which main characteristics may be compared with the stationary (no acoustic modulations) conical flame properties: …”

Section: Acoustic Modulation and Spray Flamesmentioning

confidence: 99%

Examples of the Potential of DNS for the Understanding of Reactive Multiphase Flows

Réveillon

Pera

Bouali

2011

International Journal of Spray and Combustion Dynamics

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The objective of this article is to point out the ability of the multiphase flow DNS (Direct Numerical Simulation) to help to understand basic physics and to interpret some experimental observations. To illustrate the DNS' potential to give access to key phenomena involved in reactive multiphase flows, several recent results obtained by the authors are summed up with a bridge to experimental results. It includes droplet dispersion, laminar spray flame instability, spray combustion regimes or acoustic modulation effect on a two-phase flow Bunsen burner. As a perspective, two-phase flow DNS auto-ignition is considered thanks to a skeletal mechanism for the n-heptane chemistry involving 29 species and 52 reactions. Results highlight evaporating droplet effects on the auto-ignition process that is generally dramatically modified by spray distribution resulting from the turbulent fluid motion. This paper shows that DNS is a powerful tool to understand the intricate coupling between the evaporating spray, the turbulent fluid motion and the detailed chemistry, inseparable in the experimental context.

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“…Esta función de transferencia de llama en sí misma constituye una característica del sistema de combustión, y se usa para evitar descripciones complejas de las geometrías, los modelos de turbulencia, los métodos de solución, entre otros elementos, y en vez de ello establecer una relación directa entre la excitación del sistema y su respuesta en términos de la fluctuación de la tasa de calor entregada por la combustión (Figura 2). Una segunda línea de investigación se enfoca en hacer un tratamiento numérico directo del flujo a través de las ecuaciones de Navier-Stokes [2,11,12], en general basado en potentes, pero matemáticamente costosas, herramientas de aproximación, las cuales acoplan al modelo ecuaciones de combustión. Un ejemplo de este tipo de herramientas usadas en aproximaciones de la combustión inestable, por mencionar uno relevante, es el método LES (Large-Eddy Simulations) [2,10,[13][14][15][16].…”

Section: Introductionunclassified

Simulación Bidimensional De Un Sistema De Combustión Inestable

Varila

Duque-Daza

Urueña

2010

Ingeniare. Rev. chil. ing.

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RESUMENLa inestabilidad en la combustión es una condición indeseada en algunos sistemas de combustión como en turbinas de gas por ejemplo. Se refiere a la presencia autogenerada de oscilaciones en la presión que pueden afectar a la cámara de combustión y de paso llegar a generar ruido. Una reciente tendencia generalizada en los procesos de combustión apunta al uso de mezclas pobres para la reducción de contaminantes, no obstante que este tipo de mezclas son más susceptibles a la inestabilidad en la combustión. Las complicadas relaciones que gobiernan el fenómeno se pueden resumir como el acoplamiento entre la llama y la acústica del sistema. En el presente trabajo se presenta un planteamiento numérico que permite aproximarse al fenómeno a través de la solución de un modelo de combustión básico implementado computacionalmente. En este modelo se simula una autoexcitación del sistema a través de oscilaciones en la entrada de flujos de reactantes. Finalmente, se comparan los resultados de la simulación numérica con otras simulaciones y datos experimentales.Palabras clave: Inestabilidad en combustión, función de transferencia de llama, simulación numérica directa. ABSTRACT The Combustion instability is an undesirable condition reached in some combustionDonde T es el periodo de la oscilación y R e es precisamente el índice de Rayleigh. Esta relación revela la importancia de la fase existente entre las ondas q y p en la amplificación o atenuación del fenómeno (índice de Rayleigh positivo o negativo).

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Direct numerical simulation of spray flame/acoustic interactions

Cited by 15 publications

References 10 publications

Ethanol turbulent spray flame response to gas velocity modulation

Ethanol turbulent spray flame response to gas velocity modulation

Examples of the Potential of DNS for the Understanding of Reactive Multiphase Flows

Simulación Bidimensional De Un Sistema De Combustión Inestable

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