Vortex Structure and Fluid Mixing in Pulsatile Flow through Periodically Grooved Channels at Low Reynolds Numbers.

Abstract

A study of vortex structure and fluid mixing in pulsatile flow through grroved channels by numerical simulation and experimental flow visualizations is presented. The simulations correspond to experiments for pulsatile flows with / without flow reversal in two grooved channels with different cavity lengths, with Reynolds and Womersley numbers in the ranges of 46.8<Re<117 and 75<α2<367, respectively. The agreement between simulations and experiments in terms of unsteady vortex motion is satisfactory. In most cases a primary vortex grows up during the deceleration phase whthin each cavity in the lower wall and an additional vortex is generated at the upper, flat wall. The primary vortex experiences the cavity filling and emptying process. The primary vortex strength depends on Reynolds and Womersley numbers and reaches its maximum value for a specific Womersley number. The effect of cavity length is negligible at high Womersley numbers. Fluid mixing is observed from a Lagrangian viewpoint as streaklines : fluid is exchanged between cavity and channel flows, depending on the primary vortex. At high Womersley number flows, streaklines indicate the formation of long, thin figers that enter and leave the cavity.