The evolution of the large-scale structures in the impinging round jet were studied by measuring the fluctuating pressure on the impingement surface for nozzle-to-plate distances of 2.0, 3.0 and 4.0 nozzle diameters. It is found that the large-scale vortex ring structures played a much more dominant role when the nozzle-to-plate spacing was 2.0 diameters than for either 3.0 or 4.0 diameters. The results for a nozzle-to-plate spacing of 3.0 nozzle diameters more closely resembles the spacing of 4.0 diameters. The convection velocity of the different azimuthal modes were deduced from radial cross-spectra measurements. It was found that the convection velocity of all the azimuthal modes were similar and the convection speed for the structures measured with the fluctuating pressure were independent of nozzle-to-plate distance.

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