Stokes flow paths separation and recirculation cells in X-junctions of varying angle

CACHILE M.; TALON L.; GOMBA J. M.; HULIN J. P.; AURADOU H.

PHYSICS OF FLUIDS

AMER INST PHYSICS

Año: 2012 vol. 24 p. 217041 - 217047

1070-6631

Fluid and solute transfer in X-junctions between straight channels is shown to depend critically onthe junction angle in the Stokes flow regime. Experimentally, water and a water-dye solution areinjected at equal flow rates in two facing channels of the junction: Planar Laser Induced Fluorescence (PLIF) measurements show that the largest part of each injected fluid ?bounces back? preferentially into the outlet channel at the lowest angle to the injection; this is opposite to the inertial case and requires a high curvature of the corresponding streamlines. The proportion of this fluid in the other channel decreases from 50% at = 90◦ to zero at a threshold angle. These counterintuitive features reflect the minimization of energy dissipation for Stokes flows. Finite elements numerical simulations of a 2D Stokes flow of equivalent geometry confirm these results and show that, below the threshold angle c = 33.8◦, recirculation cells are present in the center part of the junction and separate the two injected flows of the two solutions. Reducing further leads to the appearance of new recirculation cells with lower flow velocities