OCR Text |
Show - 10 - The dependency of the sound pressure P on the burning velocity S and mean _ 0 u fl ow ve I 0 ity U also agree well with experimentaI rcsu It, I· .e., P o ex S tL 1.65;;J.U .4. This result must be basic knowledge to suppress combustion noise. However, only this rclation seem insufficien t for practical purpose. We need more knowlcdge on basic charactcristics of com bustion noise. CONCLUDING REMARKS In recent studies, the sound emitted from a turbulent premixed flame has been examined by analyizing the spectra of sound fr quencies[9,10] and the movement of local flame fronts. The major differcnce betwecn the spectra of sound with turbulent flames and one without flame can be found at the low Jr quency component below 2 kHz. The intensity of the sound pressure at frequencies below 2 kHz increases to a maximum near the equivalence ratio ¢= 1.1) while that above 2kHz is independent of cp, i.e., the sound pressure to which energy is supplied by combustion is in the range of frequencies below 2 kHz. The variation of sound pressure at frequencies below 2 kHz is proportional to the 1.65th power of the laminar burning velocity Su and the l.4th power of the mean mixture stream velocity U. Using a model proposed on the basis of the experimentally revealed facts, the sound pressure can be predicted. The sound pressure is proportional to the 0.5th power of the kinetic energy conversion rate (, the square of StL and the 1.5th power of U. These results of prediction agree well with experimental result. A good correlation has been found between the measured sound and flame front movements. However, for the application of this correlation to the suppression of combustion noise, further studies arc needed on basic haracteristics of com bustion noise. |