FOR AERONAUTICS

The stability of systems contafning a beat source is examined from the energy pdnt of view. Rayleigh's criterion is derived. Inthecase of a flame, it is found that Rayleigh's criterion must be modified sl5gh-Q if the specific-heat ratios 7 of the burnedandunburnedgases sre different.. IMFR0DuCT10N It haa long beenknownthatoscillatory phenomena sre of comn occurrence in systems containing an energy source, whether it is distrib-uted in space or concentrated Fn a Umited region (e.g., in a plane or a surface). Somety-picalexamples are the scresmlng and chugging of afterburners and combustion chambers, as well as the more classical exsnples, such as the Rijke tone, the singing flame, and the oscillatory flame propagation in a tube. Generally speak-, the phenomena possess two chsracteristics. First, an oscillation is built up without any appre-ciable external excitation. Secondly, after the oscillation has increase