Extreme Plasma Modeling for Planetary Entry and Space Exploration

Overview

To date, only seven spacecraft have successfully landed on the surface of Mars. One of the key technologies that enables entry, descent and landing (EDL)—an extremely challenging endeavor—is the spacecraft’s heat shield. The shield is designed to protect the payload from intense heat and pressure loading. Replicating this phenomenon in ground-based facilities is challenging, but crucial for validating thermal protection system (TPS) materials. High-enthalpy arc jet wind tunnels are the established ground-test technology used to evaluate the performance of the TPS materials. These tunnels are used in support of all NASA exploration missions that involve atmospheric entry, both human and robotic. Arc jets produce highly energetic plasma flows to replicate the extreme aerothermal heating conditions experienced by spacecraft during EDL. Computational fluid dynamics (CFD) modeling is crucial in interpreting the data obtained from this testing. The ARC Heater Simulator (ARCHeS) analysis tool, developed at the NASA Advanced Supercomputing (NAS) facility, is helping engineers and researchers understand the complex plasma flow behavior inside arc jet wind tunnels.

Project Details

ARCHeS is an unstructured finite-volume flow solver developed by NAS researchers within the OpenFOAM framework. Through massively parallelized coupling of the Navier-Stokes, Maxwell, and radiative heat transfer equations, it is capable of modeling unsteady three-dimensional, multi-scale, multi-physics plasma flows. Such a high-fidelity model is pivotal to achieving accurate prediction of the nozzle inlet conditions. These inlet conditions are required by CFD models for interpreting arc jet tests, but historically have been approximated. ARCHeS provides a better estimate of the nozzle inlet conditions.

On a broad scale, ARCHeS serves to improve the understanding of the arc jet facility operational envelope, guide test setup conditions, and optimize current operational capability. The magnetohydrodynamics (MHD) simulation capabilities of ARCHeS may be also extended to other technologies, such as in-space propulsion.

Results and Impact

ARCHeS has proven to be efficient at attaining convergence on very stiff non-linear systems encountered in plasma flow applications. Simulations of the Aerodynamic Heating Facility (AHF) at the NASA Ames Arc Jet Complex provide insight into the radiative transfer, magnetic field, imposed electric current density, and turbulence present in arc heaters. The tool has also proven suitable for capturing interactions between the electric arc and surrounding medium. For example, simulation results show that strong gradients in both the fluid and electromagnetic fields give rise to various types of instabilities, including upstream kink instabilities that drive the arc attachment at the electrodes. In addition, the magnetic field plays an essential role in characterizing the flow between the anode chamber and the nozzle throat. These findings are important for validation and verification against experimental results, and may inform maintenance schedules and new arc jet facility design upgrades.

Why HPC Matters

Results were obtained from a two-week long simulation on NASA’s Pleiades supercomputer, using 1,200 processors. These types of multi-physics simulations of extremely complex physical phenomena requiring high spatial and temporal resolutions are only possible on large HPC systems; code optimization and memory allocation are therefore crucial to save computational time and effort. This monumental endeavor is made possible through the HPC resources and services provided by the NAS facility. Even so, the spatial resolution for wall turbulence analysis remains limited due to computational limitation—further emphasizing the need for HPC resources and for ever-increasing computing power.

More Information

• Plasma Sources Science and Technology
• Ames Arc Jet Complex
• See the poster for this demonstration (PDF, 1.7MB). As shown in the NASA booth at SC18.