The goal of the Center is to develop tools and methods to achieve predictive computations, i.e., to quantify all uncertainties and errors (in other words, add error bars to simulation results) and to reduce them. This requires major advances in physical models, Uncertainty Quantification (UQ) science and computational tools.

Failure-mode analysis of hypersonic vehicles encompasses some of the most challenging problems of unsteady fluid flows, chemical kinetics, heat transfer, numerical techniques, and multi-physics integration. These problems are of key importance to the NNSA Laboratories. One major research focus of the Center concerns the high-speed flow through the supersonic combustion propulsion system (scramjet). The primary aim of this work is to add fidelity to the component models and software and to integrate them into a full-system simulation. Predictive capability, thus, requires accurate simulation of complex phenomena and their interactions: Shock/turbulence interaction and shock dynamics Fuel injection and mixing Combustion and chemical kinetics Thermal management including radiative heat transfer Shock/flame interaction Separated flows Laminar/turbulence transition

This modeling effort is supported in parallel by several in-house experiments leveraging the world-class experimental facilities of Stanford's High Temperature Gasdynamics Laboratory (HTGL). Each experiment focuses on a system component to provide physical insight and validation data for code development.

The environment associated with the unsteady failure modes of Mach 7+ flight makes the prediction of the vehicle performance very sensitive to disturbances and uncertainties. Different forms of these uncertainties and errors can be present: Irreducible uncertainties (e.g., uncertainties in flight and atmospheric conditions, in vehicle geometry and properties) Modeling uncertainties (e.g., turbulence model, combustion model) Numerical errors (e.g., discretization)

The Center's approach is based on the quantification and reduction of all these uncertainties in a "balanced" manner. In other words, the major sources of uncertainties are identified and the largest ones are first reduced, such that all sources of uncertainties are of the same order of magnitude. A fundamental characteristic of our integrated simulation environment is the ability to control the numerical errors present in the highly integrated computations using adjoint solvers. This verification capability is considered a fundamental portion of the development of the software. Thefore, verification methods are developed and implemented as an integral part of our effort at both the component and the system levels.

Moving forward beyond the five-year duration of this program, next-generation supercomputers will be based on multi-core and streaming chip architectures for which MPI protocols may not be suitable. Accordingly, the Center's codes are being developed to facilitate the transition to future architectures and allow computation at extreme scales. Additionally, the Center supports a computer science research and educational effort on next generation programming environments and compiler developments for scientific computing.