Partners with Energy

PSC collaborations with the Department of Energy

Improved Actions for Staggered Quarks

Magnetism in the Solar Dynamo:
University of Chicago

Rocket Science:
University of Illinois Urbana-Champaign

Shock Waves in Gas:
California Institute of Technology

Turbines and Turbulence:
Stanford University

A New Picture of How Metals Deform

The Edge of Reality

Shock Waves in Gas

Turbulent mixing from reshock. These two snapshots represent simulation of a Mach 10 shock wave moving left to right through light gas (violet) in a square channel ramming into gas three times denser (red). Density contours at the interface become more complicated, improving mixing between the fluids, after the transmitted shock bounces off the side wall and "reshocks" the interface. Download a larger version of this image (706KB).

A shock wave traveling in air at supersonic speed rams into a contained volume of high-density air. The turbulent mixing that occurs in shock interactions at the interface between gases of different density is an important problem in technologies such as scramjets — propulsion at hypersonic speeds — and power generation by inertial confinement fusion. It also occurs in natural phenomena such as the violent star explosions called supernovas.

This problem is the focus of research at Caltech's Center for Simulation of Dynamic Response of Materials. Using PSC's CRAY T3E, Caltech scientists Daniel Meiron and Ravi Samtaney have carried out a series of calculations aimed at developing realistic simulation capability to complement experiments in Caltech's T5 hypervelocity shock tunnel.

In 1998, with a series of 512-processor calculations, Samtaney and Meiron explored the turbulent mixing that occurs after the shock crosses the interface and bounces off a surface to "reshock" the mixing zone. These very large calculations were among the first to explore this phenomena in three dimensions.

In recent work, Samtaney zoomed in on the details of turbulence at the interface. These direct numerical simulations at fine scale will help verify the accuracy of larger-scale modeling. At much higher resolution than prior similar studies, these simulations provide a more accurate picture of reality and, as a result, show the development of "eddy shocklets" — small regions of highly compressed fluid, essentially a fine-scale version of shock waves.

"The T3E is fantastic," says Samtaney. "In sheer speed, this machine is blazing compared to others I've used. We've been able to push this kind of simulation, called isotropic turbulence, to higher levels of turbulence where you see these regions of high compression, and it's important that our models be able to handle that."

NEXT: Turbines and Turbulence

Zooming in on shocklets. At fine scale (left), simulations show vorticity (red) and divergence (blue) — a measure of how compressed a fluid is. In the companion graphic, showing divergence of the flow field, the stringy structures represent "shocklets" — very compressed regions, or high negative divergence (red). Download a larger version of this image (left, 369KB). Download a larger version of this image (181KB).