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In the present study, two-dimensional spatial correlations are calculated in the flow and the near pressure fields of two isothermal round jets at a Mach number of 0.9, computed by highly-resolved simulations using cylindrical coordinates (r , θ, z). The two jets have diameter-based Reynolds numbers of 3, 125 and 100, 000, and they are initially weakly and strongly disturbed, respectively. For both jets, correlations are evaluated between signals at a given point, namely flow fluctuations on the jet axis at the end of the potential core and pressure fluctuations in the jet near field, and 2-D fields acquired in sections (z, r). The full signals but also the axisymmetric and first azimuthal modes are considered. Overall, despite the significant differences in Reynolds number and nozzle-exit conditions, the results for the two jets are very similar. Strong levels of correlations are obtained over large spatial regions and long time periods, providing information on noise generation mechanisms. In particular, the 2-D correlation fields reveal the presence of a wavepacket-like structure growing in the jet mixing layers, centered on a correlation spot in the potential core, and peaking in amplitude around the end of the jet core, which leads to the emission of sound waves in the downstream direction.

Two-dimensional features of correlations in the flow and near pressure fields of Mach number 0.9 jets