
HPCMP Frontier Project 

OverviewFluid turbulence subjected to a stabilizing density gradient erupts in spatiotemporally intermittent patches, a phenomenon termed "stratified turbulence,'' with which we are all familiar from riding in airplanes. In addition to being patchy, stratified turbulence involves an enormous range of length scales, which are evident in figure to the right. At larger scales, the turbulence is highly anisotropic and approximately twodimensional because the buoyancy force strongly suppresses overturning motion. Below some length, called the Ozmidov length scale, threedimensional turbulence can occur. At an even smaller length, termed the Kolmogorov length scale, turbulent motion is suppressed by viscous forces. The ratio of the Ozmidov to the Kolmogorov lengths scales is related to the buoyancy Reynolds number which characterizes the dynamic range over which threedimensional turbulence can occur in a stratified flow.For research simulations to help answer questions about atmospheric and ocean turbulence at engineering length scales, they must have buoyancy Reynolds numbers near the limit of current high performance computers. The U.S. Department of Defense High Performance Computing Modernization Program has provided 750 million corehours on its largest machine to enable such simulations as part of its Frontier program. Goals
Collaborators 
(Click on images)
Vertical velocity on a
horizontal plane in high resolution simulations of turbulence. Dark
color indicates upward flow, light color downward flow. On the top is
unstratified turbulence. On the bottom is stratified turbulence that is
driven by largescale horizontal motion; note the intense turbulent
patches and the nonturbulent region near the top center of the image.
Unless very wide ranges of length and time scales are included,
simulations of stratified turbulence can neither replicate individual
patches of turbulence nor provide information on their sizes and
lifetimes; this is because stratified turbulence is inherently
multiscale and nonlinear due to the presence of a population of such
patches.
