Synthesis of Convection Velocity and Turbulence Measurements in Three-Stream Jets for Investigation of Noise Sources

Effect of non-parallel mean flow on the acoustic spectrum of heated supersonic jets: Explanation of “jet quietening”

“…In a sense, our results are consistent with the measurements of Ecker et al 16 and Stuber et al 16 whose experiments indicate that jet heating results in a reduction in convective amplification of noise sources contained within the turbulence. This can only come about through a reduction in the magnitude of the momentum flux term using our acoustic analogy model, (41).…”

“…The Harper-Bourne 11,12 and NASA experiments 2,8,9 have both found similar generic behavior as Tanna 1 and Tanna et al 14 measurements quantify the reduction in core length with an appropriate reduction in turbulence convection velocity (see Bridges & Wernet 2 also), which might indicate the weakness of the sound source in heated supersonic flows. Although the Ma and T R of these studies are somewhat beyond our concerns (involving supersonic source convection effects), Liu et al ( 17 , p.6) indicate that sound radiated by Mach waves is expected to enter at high frequencies at these speeds, hence the Shea/Stuber results 15,16 will be qualitatively applicable to the mild supersonic conditions under our consideration in which sound amplification due to turbulence/mean flow interaction (i.e. jet quietening effects) remain a low frequency phenomenon.…”

“…Owing to the fact that the square brackets in (16) vanish when using 17for c 2 , we can integrate by parts in (16) to show that the combined Green's function variable,ν(y 1 ,U), is determined by the following PDE:…”