A study of linear wavepacket models for subsonic turbulent jets using local eigenmode decomposition of PIV data

摘要: Locally-parallel linear stability theory (LST) of jet velocity profiles is revisited to study the evolution wavepackets and manner in which parabolized equations (PSE) approach models them. An adjoint-based eigenmode decomposition technique used project cross-sectional measured using time-resolved particle image velocimetry (PIV) on different families eigenmodes present LST eigenspectrum. Attention focused Kelvin–Helmholtz (K–H) projection experimental fluctuations it, since subsonic jets inflectional K–H instability only possible mechanism for amplification large-scale fluctuations, governs wavepacket evolution. Comparisons extracted by onto with PSE solutions PIV measurements are made. We show that can be divided into three main regions, classified respect Near exit, there significant mode; solution shown comprise almost exclusively mode, agreement experiments shows this mode dominates near-nozzle fluctuations. For downstream positions, becomes stable eventually merges other branches The comparison between PSE, experiment positions suggests saturation decay related a combination several marginally modes, reasonably well modeled but cannot obtained usual application locally-parallel dealing mode. In addition, empirical data at cross-section well-founded method determination amplitudes models.