| Research on the mixing noise generated by turbojet, afterburning turbojet, and rocket exhausts was completed. Changes in the sound source characteristics from subsonic to supersonic to highly supersonic exhausts were examined. Dimensional analysis showed M0, Me, Te/T0, and rho ece/(rho0c0) to be four exhaust parameters relevant to exhaust noise that change significantly from turbojets to rockets. If the exhaust of the target systems is approximated as an ideal gas of fixed composition, M0 and Te/T0 can be taken as the two independent parameters.; Published literature was examined to clarify the effect of the increase in M0 and Te/ T0 on mixing noise characteristics. It was found that the sound source region in the plume is longer and centered further downstream in rocket exhausts than in supersonic jet exhausts. Furthermore, there is a larger portion of this source region in which turbulence convection velocities remain supersonic with respect to the atmospheric speed of sound. The peak directivity angle in the overall SPL, as determined from estimates based on SAE-ARP876D, increased almost linearly from 250 to 40° as M 0 increased from 1 to 2.5. Peak directivity angles for afterburning turbojets and rockets were shown to be significantly larger. The peak frequency in the sound power spectrum increased with Ve (or, equivalently, M0), but decreased with increasing Te/T0 over the range of M0 and Te/T 0 encompassed by SAE-ARP876D.; Detailed examination of trends in radiation characteristics with M0 and Te/T 0 was possible only over the range spanned by SAE-ARP876D ( M0 = 0.4 to 2.5 and Te/ T0 up to 3.5). To explore the potential of numerical simulations to examine the variations at higher Mach numbers and temperatures, a highly simplified large eddy simulation of the flow field was used. The procedure showed promise, but the results were not entirely consistent with published trends at low Mach numbers.; Finally, easily implemented noise estimation codes were introduced. Rocket noise estimates were compared to data measured during launches of three different space launch vehicles, with favorable results. Estimated and measured normalized sound power spectral distributions for turbojets also compared well. |
