Mahan and Karchmer [15] in their review on combustion noise mentioned that direct combustion noise from open
flames has a spectrum very much similar to that of a turbulent jet. Tametal. [16] in their investigation of direct combustion
noise from auxiliary power units (APU) found that the noise spectrum was identical to that of the large turbulence
structures noise of high - speed jets (see Fig. 2). This being the case,it seems unlikely that the new noise component is direct combustion noise because we have already found in the previous section that the spectrum shape of the new noise
component is unlike that of the similarity spectrum of the large turbulence structures noise.This leads us to believe that the
new noise component of high - performance aircrafts at afterburner is most likely indirect combustion noise