Mixed LSE and EPOD based technique for multi-plane PIV measurements synchronization in separated flow condition

A combination of the Linear Stochastic Estimation (LSE) and a modified version of the Extended Proper Orthogonal Decomposition (EPOD) is proposed to link multi-plane particle image velocimetry (PIV) data describing transitional separated boundary layers. Measurements have been obtained in two orthogonal planes, which share a common line providing the spatial consistency between the data sets. A wall-normal plane, capturing the Kelvin–Helmholtz (K-H) rolls shed downstream of the bubble maximum displacement and a wall-parallel plane, capturing the main cross-flow fluctuations occurring during the break-up process, were considered. Data on the wall-normal plane were acquired at high sampling rate to track the formation and propagation of the K-H rolls. On the other hand, the structures observed in the wall-parallel plane are characterized by longer wavelength in the spanwise direction, implying that the PIV frame has to be enlarged reducing the sampling rate due to the actual PIV system constrains. Combining LSE and EPOD allows the estimation of the time-resolved dynamical features of the separated boundary layer in both planes, increasing the temporal resolution of the wall-parallel plane data. Results will clearly show that the reconstructed pseudo 3D time-resolved field preserves the statistical properties of the original (and independent) acquired datasets in the two planes.