Coherent structures in a compressible turbulent plane jet

Coherent structures represented by proper orthogonal decomposition (POD) modes from large-eddy simulation of a compressible plane jet are analyzed. The leading POD modes of the fluctuating velocity components u′, v′, and w′, and the pressure fluctuation p′ are considered. Spatial and temporal features of these modes are analyzed by the modes and the spectra of the temporal coefficients, respectively. Interactions between leading modes of u′, v′, and w′ and the relationship between the modes of u′, v′, and w′ and of the p′ are discussed. The results show that the leading mode of u′ is in the shape of longitudinal stripes, and the mode is dominated by the jet column frequency Stc. For spanwise fluctuation w′, the leading modes are a pair of modes in the shape of a train of ridges along streamwise, and they are dominated by the fundamental frequency St0. The leading modes for v′ are a pair of modes in a row of ribs. For the dominant frequencies of the v′ modes, suppression of subharmonic frequency at St0/2 and formation of sideband frequencies around (St0 ± Stc)/2 are observed. These spatiotemporal features suggest the mode of v′ is modulated by the modes of u′ and w′. Both the leading modes of p′ and of v′ are in the shape of puffs outside the averaged shear layer. These puff modes are related as an oscillation system, which is confirmed by the spectral-POD modes.