Seth Lichter
s-lichter@northwestern.edu
Professor
AB, Harvard University
PhD, Massachusetts Institute of Technology
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Seth Lichter Professor |
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Fluid mechanics: contact line physics, vorticity dynamics
In fluid mechanics, one is usually faced with known equations (for example, the Navier-Stokes equations) which must be simplified into tractability while maintaining the relevant physical complexity. It is therefore exciting to be working on a problem for which the relevant equations are not known! In particular, it has been observed that within a few molecular diameters of a solid or a free surface Newtonian fluids show non-Newtonian behavior. This anomalous behavior is understood neither in its general features nor its underlying mechanism. The most challenging problem is to formulate the equations which describe how a fluid near a meniscus behaves under dynamic conditions. We are using statistical mechanics to probe the molecular dynamics in the meniscus region. We are also conducting experiments in which we can alter the fluid structure near a solid interface in a controllable manner. Though the differences from expected behavior occur only at microscopic distances from interfaces, the consequences of these effects are huge. For example, in order to predict large-scale fluid flow due to surface tension forces, one needs to properly formulate the molecular dynamics near a moving meniscus. This work has a wide range of application: cavitation bubbles grow by the motion of a contact line; the spreading of a thin film onto a solid occurs along a moving contact line; drying is the receding of a contact line across a substrate. A widely unexplored arena is the reduced gravity environment, where the forces at the contact line may be the dominant mechanism for generating flow. In collaboration with NASA/Lewis we are investigating how fluid redistributes itself in 0-g.
Another area of research is motivated by an interest in mixing, and may lead to methods of optimizing mass and momentum transfer near solid boundaries. Observations of boundary layers reveal a wide variety of disturbances from harmonic wavetrains of large extent to compact soliton-like pulses. We are developing a simple model which reproduces many of the diverse features seen in the boundary layer. In this model, a vortex interacts with an idealized boundary layer. A particular concern is the rapid redistribution of boundary layer vorticity, that is, "bursting" of the boundary layer fluid into the outer flow. This research involves both analysis and numerical simulation, and soon we hope to add an experimental component.
Recent Publications