Eddy Convection in Developing Heated Supersonic Jets

An experimental study of the spatial distribution of integral eddy speeds in heated, supersonic free jets is presented. The physics of such jets are of immediate interest to noise-reduction approaches for tactical aircraft jet noise. In these flows, the noise produced has a strong influence from eddy speeds, particularly for radiation in peak noise directions, due to Mach wave contributions. The measurements obtained using a time-resolved Doppler global velocimetry instrument experimentally indicate a key mechanism of the role of heating in jet noise reduction relative to the classical Lighthill U8 scaling. Measurements are presented in jets issuing from an axisymmetric biconic nozzle at two conditions: total temperatures of 1.6 and 2.0 times that of the ambient and both at approximately 106 diameter Reynolds number and pressure-matched exit conditions. For the higher total temperature case, the scaled streamwise eddy convective velocities within the shear layer were measurably reduced compared to the low...