It is known and was pointed out in the previous section that the most important component of turbulent mixing noise is
the noise of the large turbulence structures of the jet flow.This noise component radiates primarily in the downstream
direction .For a jet at afterburner, combustion takes place, not only inside the afterburner and the nozzle,but also well
beyond the jet core(see Fig. 1). For this reason, it is plausible that the large turbulence structures of these jets are some what different from those of heated supersonic laboratory jets . The jet fluid is not completely gaseous but is mixed with fuel droplets. This leads to the belief that the noise spectrum may also be different, as indicated in Fig. 13. To identify the
spectrum of the large turbulence structures noise,it appears that it would be more fruitful to investigate the noise spectra
radiated to large inlet angles,as is the case for laboratory jets. Fig. 19 is a superposition of the noise spectra at the 1301 and 1401 directions. The main contributions to these two spectra should come primarily from the large turbulence structures of the jet flow. This being the case ,it appears that a good representation of the large turbulence structures noise spectrum is to take the part of the spectrum common to both the 1301 and 1401 spectra .This identification leads to a spectrum shape as shown in Fig. 20. This spectrum will be referred to as the large turbulence structures noise spectrum of the F-22A jet at afterburner.