Spatial Correlations in a Transonic Jet

Abstract

properties. The data are presented from two separate experiments; one with the light sheet orientated in the streamwise direction (r–x plane) and one with the light sheet perpendicular to the flow direction (r–� plane). The instrument’s characteristics allow for the calculation and subsequent analysis of the two-point spatial correlations which are known to be relevant to the source terms in acoustics analogies where sound production is concerned. An examination of the spatial correlations demonstrates the averaged spatial evolution of the jet’s large-scale turbulent structures throughout the noise producing region. In particular, the (r–x) spatial dependence of the axial and azimuthal normal stresses manifest a oblique structure in the mixing layer regions of the flow, whereas the radial normalstressesevolvemoreuniformlytowardtheendofthepotentialcore.Quadrupolesourcetermsrelevanttothe soundproduction mechanismsare alsocalculated from which their spatial distributions areanalyzed with zerotime delay.Theanalysisofthesesourcetermsatx=D � 4showhowthepeakenergyfortheshear-noisecomponentresides on the high-speed side of the shear layer around r=D � 0:33, whereas the self-noise terms peak along the lip-line at r=D � 0:5,andaremostenergeticforthestreamwiseandazimuthalcomponentsofthevelocity.Tofullyevaluatethe quadrupole sources of noise, the space-time correlations of the full three-dimensional turbulent flowfield are required which are currently not available from experiments.