1. The region where the highest level of noise is produced in a jet is in the mixing layer around the core region.28This is where the shear is very high, and the associated velocities are also at their highest. Well downstream the flow evolves into a round jet flow, however the flow velocities are much lower than the exit condition and therefore do not radiate jet noise at comparable levels to the near exit region.28However, as with round jets there are many theories that have been proposed. In addition to studying round jets, Tam has investigated other nozzle shapes including rectangular jets. In his studies he has limited his research to low aspect-ratio nozzles. His results indicate that rectangular jets are actually similar to round jets.7,9-12References [7,9-12] show Tam's fits do indeed agree well with the experimental data. This indicates that round jet noise and rectangular jet noise are actually very similar since both can be fit to one setofgeneric spectralcurves.
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3. Recently, Tam et al. have suggested some reasoning behind the discrepancy.6-13They suggested that the reason high polar angles and low polar angles do not collapse is because they are associated with different types of noise.6-13Tamet al. broke down the jet noise into two components: one associated with the large-scale structures and from the other associated with the fine-scale turbulence.10-13He contends that the large-scale structures radiate predominately in the downstream direction, i.e., low polar angles, while the fine-scale turbulence noise dominates at the higher polar angles.10-13Tam et al argue that since there are two mechanisms generating the noise at the different angles, there is no reason why they should scale in the same manner, and hence there should be two distinct spectra associated withthe different mechanisms.