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.
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.
New results in thermohaline mixing
The density of seawater is
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:
This research is supported by the National Science Foundation