DYNAMIC MODE DECOMPOSITION OF UNSTABLE MICRO-FLOWS
We present an experimental investigation of spatio-temporal
coherent structures that describe the dynamics of electrokinetic instability with orthogonal conductivity gradient and electric field. Electrokinetic instability was visualized in a cross-shaped microchannel using time-resolved snapshots of a passive fluorescent tracer in the flow. Thereafter the experimental data were post-processed with dynamic mode decomposition (DMD) technique to identify the coherent structures in the flow. Our analysis yields spatial variation of instability modes along with their corresponding
temporal frequencies. By sequentially increasing the electric field in the experiments, we have obtained the coherent
structures for the onset of instability, appearance of higher harmonics, period-doubling bifurcations. At the onset of instability, the electrokinetic flow is characterized by a transverse mode of instability. Higher harmonics appears in the flow at higher electric field. Further increase in electric field leads to perioddoubling bifurcations and eventually chaotic flow. The coherent structures of different flow regimes provide valuable insight into the dynamics, spatio-temporal scales, and the physical mechanism of electrokinetic instability.