Flow Transition Analysis of Multiple Jets in Narrow Parallel Walls using POD and DMD

Abstract

We experimentally and numerically study the cavity oscillation of a compound jet in narrow parallel plates. Particle Image Velocimetry (PIV) obtains the time series velocity distribution with four jets. To perform the mode decomposition of the flow field, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are applied to the PIV data. The POD analysis reveals that the cavity oscillation involves two hierarchical structures: one corresponds to the cavity-scale oscillating of the jet, and the other to the advecting multiple smaller vortices. The DMD analysis classifies the oscillation modes into three categories: (i) oscillation mode on the container scale, (ii) pulsating mode on the container scale, and (iii) oscillation modes of individual jets. The results suggest that the superposition of these oscillation modes at the high flow rate is observed as cavity oscillation.