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The goal of the INSIEME PSAAP-III Center

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Our goal is to produce verified & validated ignition probability maps in the combustor, which are obtained from approximately 100,000-1,000,000 concurrent multi-fidelity ensembles run on

Exascale machines with an efficient portable HPC code. The ensembles employ a multi-fidelity approach (including DNS, LES, RANS, coarse simulations, and reduced-order models), and are

constructed by accounting for intrinsic uncertainties in the system, including variabilities in laser energy, focal position, deposition time/interval, propellant inflow conditions, chamber pressure, geometry, etc.

Figure 5: Schematics of ignition success/failure in the PSAAP-III combustor and the resulting ignition probability map.

To achieve this goal, the INSIEME PSAAP-III Center is currently undertaking research activities in several technical disciplines:

1. Computer Science: Development of scalable, portable, multi-GPU simulation codes, built on the Regent/Legion task-based parallelism framework, and capable of exploiting DoE’s heterogeneous supercomputers by efficient allocation of resources using auto-mappers.

2. Flow Physics: Development of models for cryogenic spray flashing and atomization, droplet dispersion, turbulence, turbulent combustion, shock/interface interactions, shock/droplet interactions, plasma physics, chemical kinetics, and ignition-kernel evolution in compressible turbulent multi-phase flows.

3. Uncertainty Quantification: Management and production of large-size ensembles (100,000-1,000,000 simulations) using a multi-fidelity framework integrated in the Legion runtime and incentivizing ensemble co-processing in GPUs and CPUs. Efficient exploration of uncertain space of parameters by searching for data structures hidden in subspaces.

4. Data Science: Utilization of machine learning to produce data-driven models of propellant’s primary atomization, chemical kinetics, adaptive multi-regime turbulent combustion, and low-order descriptions of ignition. Development of tools for efficient browsing of simulation data at Exascale.

5. Validation: Deployment of advanced diagnostics to characterize experimentally laser-induced ignition of cryogenic propellants under near-vacuum conditions in a subscale rocket combustor.

Figure 6: Collage of research activities being undertaken in the INSIEME PSAAP-III Center.