Wouldn't you like to know. Roadrunner belongs to the Department of Energy via Los Alamos National Lab. That means it often spends its processing time on rather ominous problems like nuclear weapons modeling and simulation to "assure the safety, security, and effectiveness of the U.S. nuclear deterrent." In other words, Roadrunner's work is super top-secret classified. But Roadrunner was willing to tell us--whilst glancing over both shoulders and dropping its voice slightly--that "models and simulations could include hydrodynamic mixing and turbulence of exotic materials under extreme conditions - temperatures at the core of the sun, time scales in the microseconds, and velocities of millions of miles per hour."