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Bill Smyth Professor (541) 737-3029 |
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TURBULENCE THEORY AND MODELING
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.
A turbulence primer (PDF, 1.4Mb)
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
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
And now
for something completely different
Download
recent
publications
Software to solve the
viscous Taylor-Goldstien equation
This
research is supported by the National Science Foundation