Numerical investigation of shear layer effect on sound generation in jet diffusion flame

Abstract

Shear layer effect was pointed out to be associated with the vortex-flame interaction and leads to the difference in combustion noise. In this work, numerical simulation combining with an acoustic analogy equation was performed to investigate the shear layer effect on the sound generation by jet diffusion flames. To easily identify the cause and effect, the approach that varies the thickness of shear layer by changing the Prandtl number is adopted, which provides deeper physical insight into the characteristics of the acoustic near field. The formation and evolution mechanisms of sound sources in jet diffusion flames are interpreted. It is observed that the sound sources are concentrated in vortex centers and appear as either the sources or the drains for the sound waves. The spectral analysis shows that the low frequency sound is emitted from the flame base, while the high frequency sound is radiated from the downstream region. Moreover, the theoretical analysis based on vortical dynamics shows that the low frequency sound is primarily affected by the combustion-induced buoyancy effect, whereas the high frequency sound is determined by the baroclinic torque.

Early Detection of Coal Spontaneous Combustion by Complex Acoustic Waves in a Concealed Fire Source

“…In terms of the propagation characteristics of the sound waves to be measured that are emitted inside the area to be measured, the combustion sound is generated by the low frequency vibrations in the surrounding air medium excited upon molecular collisions from inside the heated object . Combustion sound has the characteristics of sound waves, follows the propagation of sound waves, and has a large penetration depth and propagation distance. , Acoustic receivers can be used to distinguish combustion sound from other infrasonic waves in the environment and identify the combustion sound produced by loose coal spontaneous combustion. Combining the principles of acoustics with the mechanism of spontaneous combustion, a robust theory can be elaborated to support the development of coal acoustic thermometry technologies.…”

“… 80 Combustion sound has the characteristics of sound waves, follows the propagation of sound waves, and has a large penetration depth and propagation distance. 81 , 82 Acoustic receivers can be used to distinguish combustion sound from other infrasonic waves in the environment and identify the combustion sound produced by loose coal spontaneous combustion. Combining the principles of acoustics with the mechanism of spontaneous combustion, a robust theory can be elaborated to support the development of coal acoustic thermometry technologies.…”

Large eddy simulation on combustion noise in a non-premixed turbulent free flame: Effect of oxygen enhancement

“…Xiong and Jiang carried out a numerical investigation about shear layer effect on sound generation in a non-premixed jet flame. They found that distortion of flame surface in the vicinity of the burner nozzle affects the peak and its frequency in the noise spectrum [15]. Shoji et al experimentally studied relation between flame structure and mean velocity/vorticity fields and its effect on heat release fluctuation and the resulting direct combustion noise radiated from a lean-premixed H2/air turbulent jet flame.…”