Random Motions in Fluids at Small Scales

 

Kenny Breuer

Division of Engineering

Brown University

 

We will discuss the results of two projects concerning the mechanics of fluids at small  scales.  For this talk, we will concentrate on the effects of different kinds of random motion on the dynamics of the fluid and particles suspended in the fluid.

 

In the first project, we will explore motion of sub-micron particles in a shear flow, located within a few nanometers of a solid surface.  This problem was originally motivatved by the development of Particle Tracking Velocimetry at the nanoscale, but it has many interesting features in its own right, deriving from the coupled effects of Brownian motion, fluid shear, and the presence of the solid boundary.

 

In the second project, we study the motion of micron-sized bacteria as they swim in a fluid, propelled by the rotation of nanometer-sized helical flagellae that are driven by molecular motors.  The random motion of the flagellae not only propels the bacterial cells, but also mixes up the surrounding fluid, enhancing the apparent diffusion coefficient by orders of magnitude. Most interesting, however, is the observation that the random flagellar motion self-organizes, resulting in a collective fluid motion observed at the macroscale.