Papers & Reports 2020

A validated computational fluid-structure interaction method applied to supersonic parachute inflation is extended to consider a unique, parallel self-contact algorithm, porosity interface conditions on the canopy, improved flow field sampling procedures for obtaining quality loading on the parachute canopy, adaptive mesh refinement, and improved treatment of thin geometries in an immersed boundary framework.
A Numerical Investigation of Parachute Deployment in Supersonic Flow,2020 AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

High-fidelity computational fluid dynamics simulations have been carried out in order to analyze NASA’s quadrotor urban air taxi concept for urban air mobility, also know as on-demand mobility applications. High-order accurate schemes, dual-time stepping, and the delayed detached-eddy simulation model have been employed. The flow solver has been loosely coupled with a rotorcraft comprehensive analysis code. The vehicle simulated is a six-passenger quadrotor for air taxi operations.
Computational Study of NASA’s Quadrotor Urban Air Taxi Concept,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

In this work we examine a multigrid preconditioning approach in the context of a highorder tensor-product discontinuous-Galerkin spectral-element solver. We couple multigrid ideas together with memory lean and efficient tensor-product preconditioned matrix-free smoothers. Block ILU(0)-preconditioned GMRES smoothers are employed on the coarsest spaces. The performance is evaluated on nonlinear problems arising from unsteady scaleresolving solutions of the Navier–Stokes equations: separated low-Mach unsteady flow over an airfoil from laminar to turbulent flow.
Multigrid Preconditioning for a Space-Time Spectral-Element Discontinuous-Galerkin Solver,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

Unsteady Pressure-Sensitive Paint (unsteady-PSP) has recently proven that it can be an essential tool for assessing launch vehicle buffet loads by providing fine spatial coverage that naturally augments the data provided by discrete dynamic pressure sensors. These results have led to increased interest in using full-coverage unsteady-PSP data in the core development of distributed buffet load environments. This means acquiring unsteady-PSP data across the relevant parameter space and with high enough quality to be useful in quantitative analyses.
Development of Unsteady-PSP Data Processing and Analysis Tools for the NASA Ames Unitary 11ft Wind Tunnel,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

Asteroid impacts are among the few natural disasters that can be mitigated by human intervention. In previous asteroid impact risk analyses, the capacity to prevent the disaster by deflection missions has not been taken into account. Here we present a new method that accounts for the effects of deflection missions applied to the fictitious asteroid impact scenario 2019 PDC. We employ a Monte Carlo (MC) simulation approach that samples the multidimensional uncertainty space for orbit and asteroid properties.
Considering Deflection Missions for Asteroid Impact Risk,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

This paper analyzes and compares three different band-averaging models to reduce the computational cost of determining the radiative heat transfer in air plasma in Local Thermodynamic Equilibrium (LTE). The study was conducted within a cylindrical slab, but the approach to generate the reduced opacity data can be applied to solve the Radiative Transfer Equation (RTE) for any geometry in a very cost-effective way.
Analysis of Three Multi-Band Models for Radiative Heat Transfer in LTE Air Plasma,2020 AIAA Aerospace Sciences Meeting,AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

This paper covers the design and first measurements of non-perturbative, external inductive magnetic diagnostics for arcjet constrictors which can measure the motion of the arc currentchannel. These measurements of arc motion are motivated by previous simulations using the ARC Heater Simulator (ARCHeS), which predicted unsteady arc motion due to the magnetic kink instability.
Preliminary Measurements of the Motion of Arcjet Current Channel Using Inductive Magnetic Probes,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

We assess the performance of two iterative mesh optimization algorithms for generating high-order, metric-conforming meshes appropriate for use with high-order, finite-element methods. The three key steps in these metric-based approaches are: 1) obtain the desired high-order, Riemannian metric field, 2) generate a linear, metric-conforming mesh, and 3) place the high-order geometry nodes such that the mesh-implied metric conforms to the desired metric field.
Comparison of Algorithms for High-Order, Metric-Based Mesh Optimization, 2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

Two Reynolds-averaged Navier-Stokes codes, FUN3D and OVERFLOW, are used to assess the capability of Spalart-Allmaras-based turbulence models to predict the flow over the NASA Juncture Flow model. Both free-air and in-tunnel simulations are performed. While the tunnel walls have some influence, it is found to be relatively minor in the juncture region of interest. Results from the two codes are found to be consistent with each other in attached flow regions, but results in the area of separation still show grid and code sensitivity, even on grids as large as 400 million unknowns.
Reynolds-Averaged Navier-Stokes Computations of the NASA Juncture Flow Model Using FUN3D and OVERFLOW,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

A joint effort between the NASA Ames and Langley Research Centers was undertaken to analyze the Mach 0.745 variant of the Boeing Transonic Truss-Braced Wing (TTBW) Design. Two different flow solvers, LAVA and USM3D, were used to predict the TTBW flight performance. Sensitivity studies related to mesh resolution and numerical schemes were conducted to define best practices for this type of geometry and flow regime. Validation efforts compared the numerical simulation results of various modeling methods against experimental data taken from the NASA Ames 11-foot Unitary Wind Tunnel experimental data.
Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

Development of a powered descent capability for atmospheric environments is heavily reliant on computational simulation. The prohibitive computational cost of such simulations motivates an improvement in the understanding of the minimum computational fidelity required to accurately characterize aerodynamic-propulsive interference for such applications. This work examines the applicability of detached eddy simulation methods for retropropulsion in atmospheric environments through utilization of a GPU-accelerated computational framework, yielding data that are largely unachievable with conventional high-performance computing resources.
Effects of Spatial Resolution on Retropropulsion Aerodynamics in an Atmospheric Environment, 2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

Arc-jets are essential facilities used in the research, development and evaluation of thermal protection systems for hypersonic vehicles since they can reproduce the high-enthalpy environments seen during planetary entry. A test campaign is underway in the Hypersonic Materials Environmental Test System arc-jet, in support of the oncoming Mars 2020 mission to screen the response of the PICA-NuSil system. High-fidelity thermochemical non-equilibrium computational fluid dynamics simulations have been carried out to assist the test campaign by simulating the complete test matrix for the facility.
High-Fidelity Numerical Analysis of Arc-Jet Aerothermal Environments,2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020

A new methodology to construct three-dimensional, temporally stationary but spatially inhomogeneous, incompressible turbulence is presented. The method combines use of the data-driven spectral proper orthogonal decomposition (SPOD) to identify and isolate large-scale coherent motions of the flow, together with a physics-based enrichment algorithm using spatiotemporally localized Gabor modes that capture the inertial subrange turbulence.
Broadband Reconstruction of Inhomogeneous Turbulence using Spectral Proper Orthogonal Decomposition and Gabor Modes,Journal of Fluid Mechanics, vol. 888, February 2020

Synoptic magnetograms provide us with knowledge about the evolution of magnetic fields on the solar surface and present important information for forecasting future solar activity. In this work, poloidal and toroidal magnetic field components derived from synoptic magnetograms are assimilated, using the Ensemble Kalman Filter method, into a mean-field dynamo model based on Parker's migratory dynamo theory complemented by magnetic helicity conservation.
Application of Synoptic Magnetograms to Global Solar Activity Forecast,The Astrophysical Journal, vol. 890, no. 1, February 10, 2020

This paper presents takeoff trajectory computations for a typical lift+cruise small transport aircraft suitable for an urban air taxi. The selected wing–body model consists of lifting and pushing propellers. Flow is modeled using the Navier–Stokes equations. A procedure is developed to embed the trajectory motion equations in an overset grid topology along with rotating blades. Results are validated with lifting line theory computations. A typical takeoff scenario is demonstrated by time-accurately integrating trajectory equations with the flow equations. The present work extends the capabilities of the current Navier–Stokes solvers to simulate trajectory motions of urban air taxi configurations.
Takeoff Simulation of Lift+Cruise Air Taxi by Using Navier–Stokes Equations,AIAA Journal, February 17, 2020

A fine pointing capability has been developed for laser beam pointing to augment body pointing by CubeSats. An application is made to CubeSats in Low Lunar Orbit (LLO), at 100 km. Body pointing was used by Aerospace Corporation for CubeSats in LEO in NASA’s Optical Communications and Sensors Demonstration (OCSD) program. Computer simulations of this fine pointing capability have been applied to the OCSD program.
Free-space Optical Communication for CubeSats in Low Lunar Orbit: LLO,Proceedings Volume 11272, Free-Space Laser Communications XXXII, March 2020

In this work, unsteady effects present in a ship airwake are further analyzed. The effort is performed in the context of simulation of helicopter launch and recovery operations under a realistic atmospheric inflow. A ship airwake is formed as a combination of the natural wind speed and ship motion, and the incoming flow is turbulent due to the presence of an atmospheric boundary layer (ABL). On a helicopter–ship dynamic interface simulation, accounting for the effects of an ABL can be important. ABLs are different from typical engineering boundary layers, such as one over a flat plate.
Effects of Atmospheric Turbulence Unsteadiness on Ship Airwakes and Helicopter Dynamics,Journal of Aircraft, vol. 57, no. 3, May 2020

In this study, three techniques are investigated for estimating the direction in these microstructures, obtained on Cartesian grids using microtomography as grayscale values: a common image processing technique called structure tensor, a method based on artificial flux, and a novel ray-casting approach.
Anisotropic Analysis of Fibrous and Woven Materials Part 1: Estimation of Local Orientation,Computational Materials Science, vol. 178, June 2020

This presentations covers work for NASA's Commercial Supersonic Technology project to predict jet noise using wall-modeled large-eddy simulations.
Jet Noise Predictions with Wall-Modeled LESSpring 2020 Acoustics Technical Working Group Meeting, April 7-8, 2020

We perform an analysis of the line-of-sight (LOS) observables of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) for models of the solar atmosphere heated by precipitating high-energy electrons during solar flares. The radiative hydrodynamic (RADYN) flare models are obtained from the F-CHROMA database.
Response of SDO/HMI Observables to Heating of the Solar Atmosphere by Precipitating High-energy Electrons,The Astrophysical Journal, vol. 893, no. 1, April 9, 2020

Sunquakes are one of the more distinct secondary phenomena related to solar flares, where energy deposition in the lower layers of the Sun's atmosphere excites acoustic waves easily visible in photospheric dopplergrams. We explore two possible excitation mechanisms of sunquakes in the context of the electron beam hypothesis: an instantaneous transfer of momentum and a gradual applied force due to flare eruption.
Estimation of Key Sunquake Parameters through Hydrodynamic Modeling and Cross-correlation Analysis,The Astrophysical Journal, vol. 895, no. 1, May 26, 2020

Two distinct simulation methodologies: Delayed Detached Eddy Simulation (DDES) and stress based Wall-modelled Large Eddy Simulation (WMLES) are evaluated using structured overset curvilinear grids for the NASA juncture flow model. While both methodologies are shown to mitigate the primary shortcomings of steady state Reynolds Averaged Navier Stokes (RANS) simulations, several unresolved aspects are identified. Strong sensitivity to RANS-type grid refinement is observed in the DDES with a substantial deterioration of the solution quality with increasing spatial resolution associated with deficiencies in the shielding function.

Current best-practices for mesh generation in a structured overset framework are evaluated to determine their effects on the accuracy and convergence of the flow solution on a two-dimensional sectional cut of the High-Lift Common Research Model (HLCRM) wing. Mesh parameters are varied independently and correlated with force and moment coefficients from the flow solutions to identify the trends and sensitivities of the parameter variations, and the characteristics of a best practice mesh. Grid convergence and mesh adaption studies are also performed to determine the minimum mesh quality needed in order for solution-based adaption to reach an accurate flow solution.
Mesh Effects on Flow Solutions for a 2-D Multi-Element Airfoil Using Structured Overset Methods,2020 AIAA Aviation Forum (virtual), June 15-19, 2020

Computational fluid dynamics through the solution of the Navier–Stokes equations with turbulence models has become commonplace. However, simply solving these equations is not sufficient to be able to perform efficient design optimization with a flow solver in the loop. This paper discusses the recommendations for developing a flow solver that is suitable for efficient aerodynamic and multidisciplinary design optimization. One of the major recommendations is to be able to load the flow solver as a library that provides direct memory access to the relevant data.
ADflow: An Open-Source Computational Fluid Dynamics Solver for Aerodynamic and Multidisciplinary Optimization,Journal of Aerospace Information Systems, vol. 17, no. 9, September 2020

We describe the process and outcome of our efforts to port a legacy Fortran benchmark code to heterogeneous GPU-accelerated computing architectures using OpenMP. The benchmark code is one of the multi-zone NAS Parallel Benchmarks (NPB-MZ) called SP-MZ. This “mini-app” mimics the computation and data movement that is found in popular legacy and modern implicit computational fluid dynamics (CFD) solvers.
Enabling Execution of a Legacy CFD Mini Application on Accelerators Using OpenMPInternational Conference on High Performance Computing, Lecture Notes in Computer Science, June 15, 2020

The authors of this white paper met on 16-17 January 2020 at the New Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that brought together a group of heliophysicists, data providers,expert modelers, and computer/data scientists. Their objective was to discuss critical developments and prospects of the application of machine and/or deep learning techniques for data analysis, modeling and forecasting in Heliophysics, and to shape a strategy for further developments in the field. The workshop combined a set of plenary sessions featuring invited introductory talks interleaved with a set of open discussion sessions. The outcome of the discussion is encapsulated in this white paper that also features a top-level list of recommendations agreed by participants.
Machine Learning in Heliophysics and Space Weather Forecasting: A white paper of Finding and CecommendationsSAO/NASA Astrophysics Data System, June 19, 2020

This paper summarizes important areas of study to supportspacecraft mission design for in situ planetary defense missions to near-Earth objects (NEOs), including missions for reconnaissance and mitigation. The topics include: planetary defense mission design and relevant properties of an Earth-impacting NEO; reconnaissance/characterization of NEOs for planetary defense purposes; uncertainties in NEO properties, associated modeling uncertainties, and methods for addressing those uncertainties in the mission design process; launch vehicle infrastructure and mission architectures for planetary defense campaigns; and the need for research addressing unique mission design challenges posed by long-period/hyperbolic comets.
Research and Analysis for Planetary Defense In Situ Spacecraft Missions to Near-Earth Objects,White Paper, Lunar and Planetary Science and Exploration, July 2020

In this study, we analyze the evolution of the He I 10830 Å emission in numerical models and compare it with observations. The models represent the RADYN simulation results obtained from the F-CHROMA database. We consider the models with the injected electron spectra parameters close to observational estimates for the 2013 August 17 flare event in detail, as well as other available models.
Comparison of Enhanced Absorption in He I 10830 Å in Observations and Modeling during the Early Phase of a Solar FlareThe Astrophysical Journal Letters, vol. 897, no. 1, June 26, 2020

In this work, we present a framework for deriving an adaptive spacecraft attitude controller using deep reinforcement learning. The controller developed is shown to effectively perform large-angle slew maneuvers at industry-standard pointing accuracies. We find that the controller is capable of adapting in the presence of various disturbance torques unseen during training and is system-agnostic of the spacecraft being controlled, even when trained on one spacecraft configuration.
Adaptive Continuous Control of Spacecraft Attitude Using Deep Reinforcement Learning,2020 AAS/AIAA Astrodynamics Specialist Conference, August 2020

Feasibility of outer mold line (OML) heat exchangers for electrified aircraft is computationally explored for three different aircraft concepts within The High-efficiency Electrified Aircraft Thermal Research (HEATheR) project. The sensitivity of the heat transfer analysis to the computational grid, aircraft angle of attack, surface temperature, and the interaction of individual OML heat exchanger patches were investigated.
Computational Evaluation of an OML-based Heat Exchanger Concept for HEATheR2020 AIAA/IEEE Electric Aircraft Technologies Symposium (EATS), August 2020

Feasibility of outer mold line (OML) heat exchangers for electrified aircraft is computationally explored for three different aircraft concepts within The High-efficiency Electrified Aircraft Thermal Research (HEATheR) project. The sensitivity of the heat transfer analysis to the computational grid, aircraft angle of attack, surface temperature, and the interaction of individual OML heat exchanger patches were investigated.
Anisotropic Analysis of Fibrous and Woven Materials Part 2: Computation of Effective ConductivityComputational Materials Science, vol. 186, January 2021

The impact of radiation dramatically increases at high altitudes in the Earth’s atmosphere and in space. Therefore, monitoring and access to radiation environment measurements are critical for estimating the radiation exposure risks of aircraft and spacecraft crews and the impact of space weather disturbances on electronics. Addressing these needs requires reliable access to multi-source radiation environment data and enhanced visualization and search capabilities. The Radiation Data Portal provides an interactive web-based application for convenient search and visualization of inflight radiation measurements.
Understanding Radiation Environment at Earth and Beyond: Overview of Two Projects,Space Weather Operations and Research Infrastructure Workshop, Part 2, Septermber 9-11, 2020

About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the 'hot Neptune desert') has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert.
An Ultrahot Neptune in the Neptune Desert,Nature Astronomy: Letters, vol. 4, September 14, 2020

While machine learning and spacecraft autonomy continue to gain research interest, significant work remains to be done in efficiently applying modern machine learning techniques to problems in spaceflight. This study presents a framework for deriving a discrete neural spacecraft attitude controller using reinforcement learning, a paradigm of machine learning, without the need for high-performance computing.
Autonomous Spacecraft Attitude Control Using Deep Reinforcement Learning,71st International Astronautical Congress, October 2020

A smooth version of the local correlation-based transition model (LM2015) for the Spalart–Allmaras (SA) turbulence model is presented. The LM2015 model with helicity-based crossflow correlations is modified and coupled to the SA turbulence model, designated SA-LM2015.
Smooth Local Correlation-Based Transition Model for the Spalart–Allmaras Turbulence Model,AIAA Journal of Aeronautics and Astronautics, vol. 59, no. 2, February 2021

The Radiation Data Portal represents an interactive web-based application for search and visualization of in-flight radiation measurements. The portal enhances the exploration capabilities of various properties of the radiation environment and provides measurements of dose rates along with information on space weather-related conditions.
Radiation Data Portal: Integration of Radiation Measurements at the Aviation Altitudes and Solar-Terrestrial Environment Observations,AGU Space Weather, vol. 19, issue 1, January 2021

The next decade will be an exciting period for solar astrophysics, as new ground- and space-based instrumentation will provide unprecedented observations of the solar atmosphere and heliosphere. In this white paper, we summarize recent numerical achievements to reproduce structure, dynamics, and observed phenomena from the photosphere to the low corona and outline challenges we expect to face for the interpretation of future observations.
Challenges and Advances in Modeling of the Solar Atmosphere: A White Paper of Findings and RecommendationsarXiv:2101.00011 [astro-ph.IM], December 30, 2020