Unsteady Planar Base Flow Investigation Using Particle Image Velocimetry and Proper Orthogonal Decomposition

Abstract

*† ‡ Particle Image Velocimetry is applied to unsteady planar compressible base flows in the transonic and supersonic regime to obtain mean and instantaneous velocity fields. The instantaneous fields are analysed by Proper Orthogonal Decomposition to investigate the unsteady flow organisation, as revealed by the associated eigenmodes. The results indicate that two dominant eigenmodes exist in the transonic case, characterised by streamwisealigned regions of alternating upward and downward velocity fluctuations, corresponding to sinuous wake motion. A single dominant eigenmode exists in the supersonic case, characterised by large axisymmetric streamwise velocity fluctuations, corresponding to a wake pulsating motion. The out-of-plane vorticity spatial distributions associated to each eigenmode further highlight coherent flow features. Structural coherence degeneration in the supersonic case is thought to be associated with the increasing role of three-dimensional effects with compressibility.