Investigations of vortex formation in microbifurcations

The paper is dedicated to experimental studies and numerical simulations of viscous and viscoelastic flows in microchannels. The present work investigates separation phenomena and the formation of vortical structures in two microbifurcations with one closed branch: (1) Y-bifurcation with a square cross section and (2) T-bifurcation with trapezoidal sections and small aspect ratios depth/width. The main goal of the study is to characterize the dynamics of the vortex from the vicinity of Y-bifurcation and to emphasize the changes induced by the presence of elasticity on the local path lines. Velocity measurements and flow pattern visualizations of Newtonian fluid (deionized water) and weakly elastic polymer solution (low concentration of polyacrylamide in water) are obtained using a mu PIV system. Numerical computations are performed in 2D and 3D flow configurations with the commercial FLUENT code. The Newtonian simulations offer very precise descriptions of the vortical structures for all flow regimes. In the case of polymer solution, the comparison between experimental data and numerical solutions for generalized Newtonian models prove the dominant role of elasticity in modifications induced on the vortical patterns in the analyzed microgeometries. The present topic is of great interest in developing novel microfluidic applications which require precise control of the hydrodynamics of viscoelastic fluids in the vicinity of complex geometries and patterned surfaces.