This study investigates the electroosmotic flow of viscoelastic fluids past single and double microcylinders confined in a microchannel using numerical simulations based on the Oldroyd-B constitutive model coupled with the Poisson–Boltzmann equation. The governing equations were solved in OpenFOAM over a broad range of conditions: Weissenberg number, \(1< Wi < 20\) ; electrical field strength, \(33333< E_{x} < 66{,}666\) V/m; wall zeta potential, \(-5<\zeta < 30\) mV, blockage ratio, \(0.4<BR<0.45\) ; and intercylinder gap, \(1.5<S<2.5\) . For a single cylinder, flow remains steady at low Weissenberg numbers but becomes unstable beyond a critical value, exhibiting electroelastic instabilities that intensify with increasing blockage ratio, electric field strength, and wall zeta potential. In the double cylinder configuration, the flow is steady and symmetric at low elasticity but transitions to unsteady and aperiodic motion at high Weissenberg numbers, with the degree of instability decreasing as the intercylinder gap widens. The results provide a mechanistic understanding of how geometric confinement, electrokinetic forcing, and fluid elasticity collectively govern flow transition and vortex dynamics in electroosmotic microflows. These findings offer guidance for designing microfluidic systems that either exploit or suppress electroelastic instabilities for efficient mixing and controlled transport of complex fluids.
