An Advanced Simulation and Computation (ASC) Academic Strategic Alliances Program (ASAP) Center

at The University of Chicago

The Center for Astrophysical Thermonuclear Flashes

Isotropic, Homogeneous Driven Turbulence Simulation on LLNL BG/P

Don Q. Lamb

SciDAC Conference Boston, MA 28 June 2007

(http://flash.uchicago.edu)

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

Homogeneous, Isotropic, Driven Turbulence Simulation Using LLNL BG/L

11 Million CPU hours (simulation ran on 65,536 processors for nearly a week of wall-clock time)

Very high resolution simulation using a high-order Godunov PPM integrator – 18563 grid points

Accurate Lagrangian sampling of inertial range – 2563 = 17 million tracer particles

Long-time steady-state evolution of a weakly compressible flow: > than a full eddy-turnover time

Wealth of high-quality data: Particle state stored at 1400 times, and grid state stored at 700 times

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

Cut-Plane Visualization of Langrangian Tracer Particles

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

FLASH Anomalous Scaling Exponents Compared Against Theory

Kolmogorov (1962)

She-Leveque (1994)

First numerical simulation with sufficient numerical statistics to rule out theories of turbulence that include intermittency

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

Synthetic Schlieren Map of Density Field

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

Discovery: Scaling Properties of Density Are Different from Those of Scalar Field

Synthetic Schlieren map highlights regions of strong density gradients (in the plane of the image), which are yellow/white

Virtually all treatments of turbulent flow assume the flow is incompressible; the corresponding Schlieren map would be purely flat – in contrast to the wealth of structure we see

Furthermore, we have discovered that the scaling properties of the density are different from the expectation that they are similar to that of a passive scalar field – comparable images of a passive scalar field show significantly less structure on small scales

We were able to discover this because the homogeneous, isotropic, compressible simulation we ran on LLNL BG/L has a dynamic range far beyond that of any other compressible simulation

The ASC/Alliances Center for Astrophysical Thermonuclear FlashesThe University of Chicago

Results of LLNL BG/L Turbulence Simulation

We have made a breakthrough in understanding and quantifying systematic statistical errors in higher-order structure functions – this is important for experiments as well as turbulent simulations

We have carried out the first turbulence simulation that is large enough to discriminate among models of turbulence that include intermittency

We have obtained new insights on fundamental properties of homogeneous, isotropic, compressible turbulence

We are making all 22.5 TB of data generated in simulation publicly available on mass storage device in Computation Institute at UofC for analysis by visitors and by turbulence scientists world-wide