An unusual phenomenon occurs to low density material, and in particular air bubbles, entrained in a fluid when flowing through a T-junction. For a range of Reynolds numbers, the flow develops two symmetric vortices. Air bubbles are forced to the center of the vortex due to the centrifugal force and are then ?trapped?, i.e. they accumulate inside the vortex. Bubbles eventually oscillate in the vortex when the flow becomes unsteady. Experiments were conducted by generating air bubbles in a variety of T-junction devices. In addition, our 3D numerical simulations have revealed a gradient of pressure, similar to vortex breakdown, that drives the flow towards the center of the T-junction creating two recirculating zones, which trap air bubbles.

Publications:

D. Vigolo, S. Radl, and H.A. Stone. Unexpected Trapping of Particles at a T-junction. PNAS, 2014; doi:10.1073/pnas.1321585111.