Combustion noise radiation by open turbulent flames

Numerical analysis of the acoustic field of reacting flows via acoustic perturbation equations

“…6a, b, c). This result corresponds with theoretical analyses [35,7,36] and experimental observations [37,2], in which low speed turbulent flames are characterized as low frequency acoustic radiators. As discussed before, the total time derivative of the density includes the effects of unsteady heat release, species and heat diffusion as well as viscous effects.…”

Further experimental results on the structure and acoustics of turbulent jet flames

“…The visible flame region (high luminosity flame surface) is seen in fig. 8 to expand with increases in the mean flow rate, consistent with previous observations (Hurle, et al 1968;Strahle and Shivashankara 1973;Shivashankara, et al 1973). All of the above observations conform to the general idea that noise generation in premixed flames is due to In non-premixed combustion, the highly distorted waveforms (sharp gradients) suggest some form of abrupt volume expansion, in the source region, randomly distributed in space and time.…”

“…Kotake and Hatta (1965) and Smith and Kilham (1963) have found the Strouhal number at the center frequency to be reasonably constant, indicating a simple "geometrical" mechanism for noise production in flames. On the other hand, Shivashankara, et al (1973) do not find this simple picture to be valid and state " ... it appears quite improper to try to use Strouhal Number to nondimensionalize combustion noise peak frequencies ... ". They also find that the acoustic spectra are, in general, broad and the mild peak always occurs in the 250-700 Hz frequency range for hydrocarbon-air flames.…”

“…Smith and Kilham (1963) made a systematic investigation of the noise output from the main flame as affected by the pilot flame mass output and found regions where the pilot flame apparently does not affect the acoustic power of the main flame. Shivashankara, et al (1973) Many associated experiments are also possible. There appears to be a general agreement that the local volumetric reaction rate in the combusting field is directly related to the noise production.…”

Experimental study of the thermal–acoustic efficiency in a long turbulent diffusion-flame burner

“…with the measured value of the acoustic pressure P, with a value } tT'his value was slightly adjusted in several cases to improve the agreement between the measured and calculated waveforms, thus avoiding according too much importance to a single member of a ^2 4 of the particle velocity V given by equation (12), and with a value of the acoustic temperature T given by equation (13).…”