Heating effects on the structure of noise sources of high-speed jets

The noise from hot, high-speed jets is not yet fully understood. Predictive models, such as JeNo from NASA Glenn, face difficulties in constructing an effective closure strategy that correctly accounts for changes in the sound sources with heating. By utilizing two databases from a large-eddy simulation of an acoustic Mach number 1.47 jet the Lighthill sound sources are analyzed in detail with respect to changes with heating. It is shown that the individual components of the Lighthill stress tensor are tightly coupled, implying they are difficult to model separately. An alternative form of Lighthill's stress tensor which attempts to more usefully isolate the various effects is presented, but is shown to be only partially successful. A form of the acoustic analogy developed by Ffowcs Williams is also applied and it is found that the noise radiated to the 30 degree aft angle is dominated by the term [δu _r̄/δy_r]δρ/δt, which is linear in the density.