The developing flow field in a parallel plate microchannel, induced by wall motion, has been modeled numerically. The flow is driven in this scenario not by an applied pressure gradient, but by the movement of the walls in the axial direction at a constant speed. This type of flow simulates the physical driving mechanism that exists in electro-osmotically generated flow with large channel diameter-to-Debye length ratios. The results are general, however, for any microscale flow induced by wall motion and resulting viscous pumping. The dynamics of the developing flow field were explored for channel length-to-hydraulic diameter ratios (aspect ratio) of 5, 10, and 20 at ten Reynolds numbers, Re (based on the wall velocity), below Re < 2000. The results show that far from the inlet the maximum fluid velocity occurs at the walls, as is expected, and the minimum velocity occurs at the channel center. Near the channel inlet, however, the centerline velocity is not a minimum but reaches a local maximum due to a resulting pressure imbalance generated by the wall motion. The ratio of the centerline velocity to wall velocity depends on the axial distance from the channel inlet, the Reynolds number and the channel aspect ratio. As the aspect ratio increases, the centerline velocity tends to approach the wall velocity far downstream from the inlet. Increases in the Reynolds number have the opposite effect on the centerline velocity. The hydrodynamic developing region, defined by that section of the channel where the wall shear stress is changing, also depends on the channel aspect ratio and Re. In general it is found that the developing region is significantly shorter than for pressure-driven flow at the same Re.

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