Unstable jet–edge interaction Part 2: Multiple frequency pressure fields

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Abstract
In Part 1 of this investigation we addressed the instantaneous pressure field at a leading-edge due to single frequency jet-edge interactions; here we consider edge pressure fields and associated vortex interaction patterns at the edge having a number of (at least six) well-defined spectral components. Each of the spectral components is present along the entire extent of the approach shear layer upstream of the edge; the relative amplitudes of these components are preserved in the conversion process from the free (approach) shear layer to the surface pressure field, the key link being complex, but ordered patterns of vortex interaction at the edge. Moreover, the predominant spectral components can be reasoned on the basis of these visualized vortex interactions by considering the vortex array in the incident shear layer.The spectral character of the surface pressure field changes dramatically with edge location in the incident shear layer, or vortex array. If the edge is symmetrically located within the vortex array of the incident jet, a low-frequency component prevails due to large-scale vortex formation; however, with an asymmetrically disposed edge, the most unstable frequency of the jet dominates due to direct vortex impingement upon the edge, and the mean-square pressure amplitude (encompassing all spectral components) is double that of the symmetrical interaction.Irrespective of the type of interaction and the manner in which energy is partitioned between spectral components, the mean-square pressure due to the sum of all spectral components decays approximately as x−c immediately downstream of the tip of the edge. However, each spectral component tends either to a maximum or minimum amplitude as the tip of the edge is approached, depending upon the class of vortex array-edge interaction.

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