Two-point laser Doppler velocimetry measurements in a Mach 1.2 cold supersonic jet for statistical aeroacoustic source model

Single and multi-point laser Doppler velocimetry measurements performed in a cold Mach 1.2 jet flow are used to assess those properties of the aerodynamic field most relevant in the generation of turbulence mixing noise. Single point measurements yield mean velocity profiles, turbulence intensity profiles and power spectral densities of both the velocity and Reynolds stress fields at seven axial stations between the jet exit and the end of the potential core. The longitudinal components of the second-order and fourth-order two-point velocity correlation tensor are obtained from a series of multi-point LDV measurements, whence a cartography of integral space and time scales, convection velocities and acoustic compactness is effected. These results are used to examine differences between subsonic and supersonic jet aerodynamics in terms of their sound generating potential. Finally analytical expressions are proposed for the spatial and temporal parts of the longitudinal correlation coefficient function. These are scaled using the integral space and time scales of the velocity and Reynolds stress fields, and excellent agreement is found with experimentally determined functions.