Clavin P.

After a brief historical review starting with the singing flames observed soon after the discovery of hydrogen, and lasting to the Rayleigh analysis developed about a century later for the thermo acoustic instabilities in combustion chambers, we will present theoretical advances and recent basic experimental results obtained during the two last decades. The first topic will concern the sound generation by freely propagating turbulent flames. The two extreme cases of a strong and a weak turbulent flow of premixed gases interacting with the flame front will be considered. The influence of the intrinsic instabilities of the flame upon the noise will be pointed out. A spectacular noise reduction that has been obtained recently for oxyacetylene torches following these basic works will be presented. The second part of this lecture will be devoted to vibratory flames propagating in tubes. In order to point out the role of the internal structure of the flame, the cases of spray and premixed gas combustion will be compared. We will also show how some of these results have been used recently to carry out new experiments on the hydrodynamic instabilities of premixed flames. The last topic will covered theoretical results obtained for the interaction of sound waves and combustion of solid propellant involved in the instabilities of rocket engines. The unsteady effects of the internal structure of the flames will be pointed out.