Tue April 22nd 2008 14:00 | Seminar | Life on the Boundary: viscous and inertial transitions in mayfly nymphs and stenotic arteries Kenneth T. Kiger |

## Details:Many interesting and important biophysical problems hinge upon a transition between different flow regimes that result from a competition between inertial and viscous diffusive effects. In the current work, two problems are presented which have in common a key transition brought about by this competition within an oscillatory flow.In the first problem, the ventilation current generated by beating of an external array of plate-like gill plates in mayfly nymphs is studied in the context of searching for a postulated bifurcation in inertial limits of thrust generation by reciprocal flapping motions. The characteristic Reynolds number associated with the gill motion changes with animal size, varying over a span of Re = O[1] to O[100] depending on age and species. Thus mayflies provide a novel system model for studying ontological changes in pumping mechanisms associated with transitions from a viscous- to inertia-dominated flow. Indeed, observation of other animals and theoretical analysis indicate that a bifurcation should exist for inertial thrust generation by a reciprocal flapper for Reynolds numbers on the order of 10-20. In the current ongoing work, the gill kinematics and resulting fluid motion is analyzed which show that the gills transition from a strongly asymmetric motion at Re < 5 to a more reciprocal motion by Re > 10. Details of the hydrodynamic mechanisms and pumping effectiveness will be discussed. In the second problem, the transition produced by a pulsatile flow within a constricted planar channel is studied as a model for the flow dynamics encountered within a stenotic artery. In general, the flow just downstream of the constriction is dominated by the dynamics of the accelerating/decelerating jet that forms during each pulsatile cycle. A 'synthetic' turbulent-like wall-layer develops, and is constantly supported by streamwise vortices that originate from the spanwise instabilities of the large coherent structures generated by the jet. The rela |