University of Guilan Computational Sciences and Engineering 2783-2503 Articles in Press 2026 04 26 Numerical Investigation of an Active Micromixer with Oscillating Elastic Wall and Mixing Chamber: Parametric Study and Optimization 9568 10.22124/cse.2026.33130.1166 EN Tohid Adibi University of Bonab Seyed Esmail Razavi University of Tabriz Journal Article 2026 02 25 This study numerically investigates mixing performance in an active micromixer combining geometric modification and oscillating wall excitation. The proposed design features two variable-angle inlets (45°, 60°, 90°, and 180°), a circular mixing chamber (R = 10 and 12.5 mm), and a flexible oscillating outlet section (2-8 Hz, 1-3.5 mm amplitude). A two-way fluid-structure interaction (FSI) approach in COMSOL Multiphysics captures the mutual effects between fluid flow and the elastic wall. Water enters at 20°C and 80°C with Reynolds numbers of 100-825 in laminar flow regime, with average outlet temperature serving as the mixing indicator.<br /> Results show that increasing oscillation frequency and amplitude enhances mixing, with 8 Hz and 3 mm identified as optimal. The 60° Y-configuration outperforms the conventional T-mixer (90°) and parallel inlet (180°). While the mixing chamber generally improves performance, its effect is less pronounced at the optimal 60° angle. Unequal inlet velocities generate Kelvin-Helmholtz instability, creating shear-induced vortices that further enhance mixing.<br /> The optimal configuration—60° inlet angle, 10 mm chamber radius, and 8 Hz, 3 mm wall oscillation—achieves a 92% mixing index at Re = 825, a 58% improvement over the base T-mixer. Estimated Nusselt numbers range from 9.2 to 13.8, with friction coefficients of 0.42-0.52. All configurations reach steady mixing within 6 seconds. These findings provide valuable insights for designing high-efficiency active micromixers for microfluidic applications requiring rapid homogenization of non-isothermal fluids.