Noise generated by turbulent non-premixed flames

Knott, P. R.

doi:10.2514/6.1971-732

Cited by 16 publications

(10 citation statements)

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“…Compared to the wealth of theoretical and experimental data on optical radiation, acoustic radiation remains to be characterized with rigor and precision when the details are concerned. Several theoretical and experimental studies supporting these general thoughts have been reported by many investigators, e.g., Strahle and coworkers (1973Strahle and coworkers ( , 1971Strahle and coworkers ( , 1976; Knott (1971); Kotake and Hatta (1965); Smith and Kilham (1963);and Plett et al (1976). Bragg (1963) presented the view that the turbulent combustion zone may be regarded as a random collection of monopole sources, the fluctuations in volume expansion (due to heat release at constant pressure), leading to acoustic pressure radiation.…”

Section: Introductionmentioning

confidence: 67%

Some Fundamental Acoustic Observations in Combusting Turbulent Jets

Ramohalli

1981

Combustion in Reactive Systems

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An experimental study has been made of the acoustic emissions from turbulent combustion zones with the specific intention of inferring the combustion details from the acoustic field. Included are data from a laboratory burner, a commercial burner tested in the laboratory, and a seven-head system of burners installed commercially on a rotary kiln. The fuels used include methane, ethane, propane, and natural gas. Based on an order-of-magnitude analysis of the turbulent combustion zone, specific frequency bands of the acoustic emissions are examined. It is found that any change in the combustion zone (air/fuel ratio) is invariably reflected in the acoustic amplitudes in three bands. Product gas analyses show that the nonefficient combustion correlates with these perceptible changes in the acoustic signatures. The theoretical reasoning and the experimental results show the feasibility of acoustically monitoring the combustion zones to infer such details as efficiency and pollutant production. The acoustic spectrum of a combustion zone reveals many details which can be deduced to be geometry dependent, flow dependent, turbulence dependent, or combustion dependent. The close interplay of these influences makes it difficult, in general, to isolate the individual effects. The simplified analysis here attempts to deduce the geometry and turbulence effects. It is consistent with the observed behavior for both premixed and nonpremixed flames. Also, this simplified analysis identifies the high-frequency zone as a possible region of acoustic emission directly influenced by combustion.Nomenclature a = sonic velocity in the ambient atmosphere, m/s 3* = distance from burner exit to microphone, m D = burner exit diameter, m

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Section: Introductionmentioning

confidence: 67%

Some Fundamental Acoustic Observations in Combusting Turbulent Jets

Ramohalli

1981

Combustion in Reactive Systems

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“…The premixed flame has indeed been observed to yield the cubic law in previous investigations also (Strahle and Shivashankara 1973). The caSe of the less explored non-premixed flame is not so certain, and many different indices have been reported in the literature (Kotake and Hatta 1965, Giammar and Putnam 1970, Knott 1971). …”

Section: The Acoustic Powermentioning

confidence: 99%

“…Here, we restrict ourselves to the noise problem, where many aspects of the problem have been clarified in recent times (Strahle and coworkers 1971,,;, Smith and Kilham 1963, Kotake and Hatta 1965, Knott 1971, Hurle, et al 1968, Giammar and Putnam 1970. An examination of the literature indicates that the following points are fairly clear.…”

Section: Introductionmentioning

confidence: 99%

“…In general, they found the acoustic pre s sure to be proportional to the sq uare of the mass flow rate, although the exponent tended to be less than two when miD (essentially the Reynolds number) was increased, and greater than two when the ill/ D was decreased. Knott (1971), in his experiments on premixed jet flames, found the acoustic power to be proportional to U 4 , and in his experiments on non-premixed flame s to be proportional to U fuel ' Although his work represents about the single most comprehensive one on the differences between the premixed and non-premixed flaITles, SOITle of this experiITlental techniques leave a few questions unanswered. His reITloval of a short length of the inner tube, in the co -flow geometry, may not be sufficient to attain premixing of the reactants.…”

Section: Introductionmentioning

confidence: 99%

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Further Experimental Results on the Structure and Acoustics of Turbulent Jet Flames

1976

Aeroacoustics: Jet Noise, Combustion and Core Engine Noise

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The structure of open turbulent jet flames is experimentally studied in the context of their noise emission characteristics. The differences between premixed and (co-flow) non-premixed flames are explored. Recent experiments repeated in an anechoic chamber complement earlier results obtained in a hard-walled bay. The reactants (methane and enriched air) are burned in the premixed, or non-premixed, mode after a length of pipe flow (t/D> 150). The thick-walled tubes anchor the flames to the tip at all of the velocities employed (maximum velocity, well over 300 ft/sec), thus eliminating uncertainties associated with external flameholders. The time-averaged appearance of the flames is obtained with still photographs (1160 sec). The detailed structures are revealed through high-speed ("" 2500 frames/sec) motion pictures. The acoustic outputs of the flames are mapped with a condenser microphone. The recorded data are played back to obtain the amplitude, waveshapes, directionalities, and frequency spectra of the noise. Profound differences are found between the premixed and non-premixed flames in their structures and noise characteristics.

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“…Three additional equations can be written in terms of the measured acoustic impedance at either end of the burner, z I = P I/V= and zII P II/VII _ (12) and the isentropic condition at thè burner inlet,…”

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confidence: 99%

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

Mahan¹

1984

The Journal of the Acoustical Society of America

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Noise generated by turbulent non-premixed flames

Cited by 16 publications

References 0 publications

Some Fundamental Acoustic Observations in Combusting Turbulent Jets

Some Fundamental Acoustic Observations in Combusting Turbulent Jets

Further Experimental Results on the Structure and Acoustics of Turbulent Jet Flames

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

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