HE study of Ref. 1 appears to be an advance in the use of computational e uid dynamics for the prediction of the properties of a turbulent jet. It yields details of the instantaneous e ow patterns and, in addition, two-point space-time correlations of velocity components. These components govern the sources of sound in Lighthill’ s 2 theory of jet noise (and in its extension 3 to dealwith waveconvection,hencerefraction);further,theircorrelationsarerequired in theintegralforthespectraand mean squareradiatedsound pressure.(Thisis amplie edfurtherinthefollowing.)Itappearsfrom the Abstract and presentation that the present work is motivated by these considerations in the context of Lighthill’ s theory. Although rms properties of a round jet must be axisymmetric, instantaneous values are not. These large-eddy simulation (LES) computations of the instantaneous velocity e eld show striking deviations from axisymmetry. The deviations are consistent with those found in the radiated sound e eld by Maestrello 4 in 1976. He measured electronically the correlations between the signals of a pair of microphones, say, A and B, at a e xed distance from the nozzle, separated in angle. For A and B in a plane at the nozzle normal to the axis, the correlation decayed with separation in azimuth angle to zero at 90 deg and then increased again to about 0.1 at 180 deg, that is, when A and B were on opposite sides of the jet. In other examples, correlations showed similar, but less extreme, decay as one microphone was moved away from the other along a circle of latitude. The low A:B correlations signify, of course, a marked departure from instantaneous sound e eld axisymmetry. The Lighthill theory can be extended to these two-microphone correlations as well: such an extension (involving approximation) showed general— in some cases striking— agreement with Maestrello’ s experimental curves: in broadband 5 and in narrow frequency bands. 6 The dominant feature governing all of the correlations is the difference in acoustic travel times to microphones A and B from a noncentral source eddy in the jet turbulence. In the e rst-discussed case of the last paragraph, the peculiar variation with azimuth angle is accounted for by the source directivity.