Bill Smyth


(541) 737-3029






Fluid turbulence represents a major unsolved problem in applied physics, as well as an essential component governing the behavior of geophysical fluid systems. Efforts to understand and parameterize turbulent mixing have been a research focus over the past several decades, and continue to be essential to improved understanding and prediction of the evolution of Earth's atmosphere and oceans.

The past decade has brought tremendous insights into the physics of turbulence, due largely to direct numerical simulations (DNS). This new understanding applies almost entirely to the simplest idealization, i.e. stationary, homogeneous, isotropic turbulence. In nature, turbulence never conforms to this simple picture. In particular, geophysical turbulence is almost always affected by ambient shear, density stratification and planetary rotation, which complicate the physics greatly. The turbulence modeling program at COAS aims to extend state-of-the-art theories of turbulence to small-scale geophysical flows by accounting for these effects.

Mixing at interfaces in the atmosphere and oceans (and why it matters)


Turbulence in shear-driven overturns

A long-term focus has been DNS of turbulence resulting from breaking Kelvin-Helmholtz billows, wavelike vortical structures that arise due to the dynamical instability of localized layers of shear and stratification. This scenario provides a useful model for many of the turbulent events that are observed in the Earth's atmosphere and oceans. The following links lead to summaries of developments in this area.

Mixing efficiency in KH Billows

Turbulent patches and banded clouds

Turbulence in Holmboe Waves


New results in thermohaline mixing

The density of seawater is controlled by two scalar properties: temperature and salinity. Because they diffuse at very different rates, they can combine to affect buoyancy and thus drive motion in some unexpected and fascinating ways. These fall under the name of double diffusion. Double diffusion was discovered in the 1960s and has been under intense study since then, but most existing studies assume that the surrounding fluid is motionless. In reality, that is almost never true. Layers of water with different temperature and salinity are usually in motion relative to one another, so that double diffusion usually coincides with shear. Shear is something this group has extensive experience with, and we therefore focus on the interaction between it and double diffusion. We recently completed an NSF Breakthrough Science project in which we conducted the first direct numerical simulation of three dimensional flow in salt water.

Click below to learn more.
Direct simulations of double diffusive turbulence

Other materials of interest:


OC670 Fall 2012

Oregon Coast Math Camp

Teaching materials for shear-driven turbulence

Download recent publications

And now for something completely different

Matlab software to solve the viscous Taylor-Goldstein problem

About the author

Questions or comments?


This research is supported by the National Science Foundation

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