Papers & Reports 2023

The exponential growth of digital image data has given rise to the need of efficient content management and retrieval tools. Despite its popularity, the VRC method comes with two very important shortcomings: it only yields good results when the data dimensionality is low and it does not scale well for a high number of clusters, making it very difficult to use in computer vision applications. We propose an extension to the VRC method that works for increased cluster number and high-dimensionality data sets and therefore is fit for image data sets.
Efficient Estimation of the Number of Clusters for High-Dimensional DataThe Journal of Defense Modeling and Simulation: Applications, Methodology, Technology, December 2023.

A new grid topology approach suitable for body-fitted structured grids is presented to time-accurately simulate deployment of parachutes. The goal is to provide an alternate to the current use of Cartesian and unstructured grids that are less desired from turbulence modeling aspects compared to the body-fitted structured grids. Time-accuracy essential for the deployment is maintained, unlike in the quasi-steady loose coupling methods used elsewhere with the Cartesian/unstructured grids. The current paper establishes the new approach for a 2D case that can lead to 3D cases.
Grid Topology for Time-Accurate Deployment Simulation of 2D Parachutes by using Navier-Stokes EquationsAerospace Science and Technology, vol. 142, part B, November 2023.

The first significant sunquake event of Solar Cycle 25 was observed during the X1.5 flare of May 10, 2022, by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory. We perform a detailed spectro-polarimetric analysis of the sunquake photospheric sources, using the Stokes profiles of the FeI 6173A line, reconstructed from the HMI linear and circular polarized filtergrams.
Spectro-Polarimetric Properties of Sunquake Sources in X1.5 Flare and Evidence for Electron and Proton Beam ImpactsarXiv:2309.07346 [astro-ph.SR], September 13, 2023.

The order of execution of computational kernels for Single-Program, Multiple-Data (SPMD) programs is usually determined at compile time. These static predetermined schedules can lead to performance issues at runtime, and are difficult to implement for inhomogeneous situations, such as variable-order or multi-physics applications. It is especially challenging to generate performant schedules when it is unknown whether specific kernels require execution, as a function of user inputs, or the kernel execution time changes dependent on the hardware. This paper presents a solution to this problem by dynamically scheduling computational kernels at runtime using directed acyclic graphs to track the data dependencies between kernels.
Automatic Runtime Scheduling Via Directed Acyclic Graphs for CFD Applications2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

Reliable boundary-layer laminar-turbulent transition predictions are critical for the design of aircraft that use natural or controlled laminar flow to achieve low drag and better fuel efficiency. During cruise flight through low turbulence, the three-dimensional boundary layer over swept surfaces can transition prematurely due to stationary crossflow instabilities induced by surface roughness. Parabolized stability equations analyses have been successfully used to explain the different phases of the transition process under well controlled perturbations such as steps or discrete roughness elements.
Computational Study of Low-Speed Boundary-Layer Laminar-Turbulent over a 30-Degree Swept Plate in a Channel2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

A multi-fidelity computational study has been conducted on NASA's quiet single-main rotor helicopter concept for urban air mobility using computational fluid dynamics and rotorcraft comprehensive analysis tools. Two approaches have been followed in order to simulate the rotor flows: (1) a rotor disk model, which models the rotors as source terms, and (2) a high-fidelity approach using high-order accurate schemes and dual-time stepping, which simulates the rotor with its individual rotating blade grids.
Multi-Fidelity Computational Analysis of a Quiet Single-Main Rotor Helicopter for Air Taxi Operations2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

With the development of urban air mobility, the safety of multirotor vehicle operations in proximity to vertiports must be assessed. This paper examines high-fidelity blade-resolved OVERFLOW simulations and medium-fidelity vortex particle-mesh simulations that capture the aerodynamics of a rotorcraft in full and partial ground effect.
Simulation of a Quadrotor Urban Air Taxi Hovering Above a Rooftop Edge2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

This paper concerns the modeling and analysis of angled active flow control microjets using Computational Fluid Dynamics (CFD). Two geometries are considered: a 2D NLR7301 two-element aerofoil with 20° flap deflection, and a 3D Common Research Model in a high lift configuration (CRM-HL) with inboard and outboard flaps deflected 40° and 37°, respectively.
Microjet Angle Sensitivity for Active Flow Control on Multi-Element High-Lift Systems2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

Recent work on automation of structured overset mesh generation has significantly reduced the manual effort required for this task. RANS-based flow solution computation on these automatically generated structured overset meshes are investigated. Comparisons are performed with flow solutions obtained on manually generated best-practice meshes of equivalent resolution. Four test cases are presented: the Juncture Flow Experiment, two concept vehicles from NASA’s Revolutionary Veritcal Lift Technology (RVLT) project, and a ducted propeller.
Aerodynamic Simulations for Complex Geometries Using Automatically Generated Structured Overset Meshes2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

An automated off-body Mach cone aligned structured curvilinear grid generation procedure is presented for near-field computational fluid dynamics simulations. This procedure combines output-based indicators and mesh redistribution to perform anisotropic mesh adaptation while maintaining Mach cone alignment. Automation is achieved through a novel direction-based adaptation indicator formulation. The adaptation procedure is demonstrated on the JAXA Wing Body geometry and X-59 C608 demonstrator model from the Second and Third AIAA Sonic Boom Prediction Workshops, respectively.
Anisotropic Mach Cone Aligned Mesh Adaptation for Low Boom Simulations2023 AIAA Aviation Forum, San Diego, CA, June 12-16, 2023.

Previous studies analyzing the evanescent nature of acoustic waves in the lower solar atmosphere, up to 300 km above the photosphere, have shown an unexpected phase shift of an order of 1 s between different heights. Those studies investigated the spectral line Fe Ιλ6173.3, commonly used for helioseismic measurements. Such phase shifts can contribute to a misinterpretation of the measured travel times in local helioseismology, complicating inferences of, e.g., the deep meridional flow. In this study, we carry out phase shift computations using a simulated, fully radiative, and convective atmosphere from which the Fe Ιλ6173.3 line is synthesized.
Nonzero Phase Shifts of Acoustic Waves in the Lower Solar Atmosphere Measured from Realistic Simulations and Their Role in Local HelioseismologyThe Astrophysical Journal, vol. 949, no. 2, June 2, 2023.

images acquired by Atmospheric Imaging Assembly (AIA) instrument on-board the Solar Dynamics Observatory have frequently displayed “spikes,” pixel regions yielding extreme number of digital counts. These spikes are regularly removed from AIA Level 1.0 images to produce clean and reliable data. A study of historical data has found over 100 trillion spikes in the past decade. This project correlates spike detection frequency with radiation environment parameters in order to generate an augmented data product from SDO.
Turning Noise Into Data: Characterization of the Van Allen Radiation Belt Using SDO Spikes DataSpace Weather, vol. 21, issue 3, March 22, 2023.

The flux of energetic particles originating from the Sun fluctuates during the solar cycles. It depends on the number and properties of Active Regions (ARs) present in a single day and associated solar activities, such as solar flares and coronal mass ejections (CMEs). Observational records of the Space Weather Prediction Center (SWPC NOAA) enable the creation of time-indexed databases containing information about ARs and particle flux enhancements, most widely known as Solar Energetic Particle events (SEPs). In this work, we utilize the data available for Solar Cycles 21-24, and the initial phase of Cycle 25 to perform a statistical analysis of the correlation between SEPs and properties of ARs inferred from the McIntosh and Hale classifications.
Statistical Study of the Correlation between Solar Energetic Particles and Properties of Active RegionsarXiv:2303.06100 [astro-ph.SR], March 10, 2023.

Solar Energetic Particle (SEP) events and their major subclass, Solar Proton Events (SPEs), can result in unfavorable consequences to numerous aspects of life and technology, making them one of the most prevalent and harmful effects of solar activity. Garnering knowledge leading up to such events by studying proton and soft X-ray (SXR) flux data to alleviate the burdens they cause is therefore critical for their forecasting.
Predicting Solar Proton Events of Solar Cycles 22-24 using GOES Proton & Soft X-Ray Flux StatisticsarXiv:2303.05446 [astro-ph.SR], March 9, 2023.

The detection of Earth-size exoplanets is a technological and data analysis challenge. Future progress in Earth-mass exoplanet detection is expected from the development of extreme precision radial velocity measurements. Increasing radial velocity precision requires developing a new physics-based data analysis methodology to discriminate planetary signals from host-star-related effects, taking stellar variability and instrumental uncertainties into account. In this work, we investigate and quantify stellar disturbances of the planet-hosting solar-type star HD121504 (G2V spectral type) from 3D radiative modeling obtained with the StellarBox code.
Modeling Stellar Jitter for the Detection of Earth-Mass Exoplanets via Precision Radial Velocity Measurements241st Meeting of the American Astronomical Society, Seattle, WA, January 8-12, 2023.

Detection of Earth-mass planets with the radial velocity method requires a precision of about 10cm/s to identify a signal caused by such a planet. At the same time, noise originating in the photospheric and subphotospheric layers of the parent star is of the order of meters per second. Understanding the physical nature of the photospheric noise (so-called stellar jitter) and characterizing it are critical for developing techniques to filter out these unwanted signals. We take advantage of current computational and technological capabilities to create 3D realistic models of stellar subsurface convection and atmospheres to characterize the photospheric jitter.
3D Realistic Modeling of Solar-Type Stars to Characterize the Stellar Jitter241st Meeting of the American Astronomical Society, Seattle, WA, January 8-12, 2023.

This study explores aerodynamic feasibility of small surface-normal pneumatic jets (microjets) for lift enhancement on the high-lift Common Research Model. To date, lift enhancement studies using microjets have been conducted at wind tunnel Reynolds numbers less than three and half million. This paper computationally investigates microjet effects at a flight Reynolds number of 24.6 million.
Aerodynamic Assessment of Surface-Normal Active Flow Control for Lift Enhancement on the High-Lift Common Research ModelAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

The Space Launch System (SLS) employs two Space Shuttle derived Solid Rocket Boosters (SRBs) which separate from the SLS core while still experiencing appreciable aerodynamic loads. Creating an aerodynamic database for this phase of flight can be challenging due to the large number of independent variables needed to fully constrain the problem and the complex flow induced by exhaust plumes of the booster separation motors (BSMs) and core main engines impinging on other parts of the vehicle. This paper details recent efforts in generating aerodynamic databases for SLS during the booster separation event using viscous Computational Fluid Dynamic (CFD) simulations obtained using NASA's FUN3D solver.
Advances in Space Launch System Booster Separation CFDAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

This paper will discuss the use of Computational Fluid Dynamics (CFD) for the Space Launch System (SLS) Program to model the ascent phase of flight. The ascent phase begins shortly after the vehicle clears the launch tower and extends to the first staging event. To model SLS’s ascent, over one thousand numerical solutions of the Navier-Stokes equations are solved, and this analysis has been repeated for five different SLS configurations. To manage this demanding ascent CFD task, the SLS program has developed the Computational Aerosciences Productivity & Execution (CAPE) software, which is introduced in the paper.
Launch Vehicle Ascent CFD for the Space Launch SystemAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

This paper is part of an effort to assess the current capability of Computational Fluid Dynamics (CFD) to accurately predict the experimental forces and base pressure on the Check Standard Model (CSM). The wind tunnel data for this model is gathered during annual monitoring of test-to-test repeatability for the Langley Unitary Plan Wind Tunnel (LUPWT). A blind database designed to help quantify the uncertainty of simulating LUPWT for the CSM repeatability tests was run using the Launch, Ascent, and Vehicle Aerodynamics (LAVA) CFD code.
LAVA CFD Analysis of the Check Standard Model with the Langley Unitary Plan Wind TunnelAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

Computational simulations using structured curvilinear overset grids with the Launch Ascent and Vehicle Aerodynamics (LAVA) framework are presented for predicting the aerodynamic and aeroacoustic behavior of a contra-rotating open rotor (CROR) propulsion system using a newly developed and computationally efficient sliding mesh technique. A comprehensive evaluation of two turbulence closure treatments is carried out as part of the scope of this work: Unsteady Reynolds-Averaged Navier-Stokes Simulation (URANS), and Hybrid RANS/LES (HRLES).
Unsteady RANS and Scale Resolving Simulations of Open Rotor NoiseAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

Mesh adaptation is essential for controlling the cost of large-scale, high-resolution simulations. We propose an efficient parallel unsteady adaptation approach that uses multiple sweeps over the time domain. The simulation is divided into a set of temporal “windows” each having a spatial mesh and time step adapted for a fraction of the total solution time.
Parallel Mesh Adaptation for Unsteady Blast Simulations on Cartesian MeshesAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

The SUSAN Electrofan is a new hybrid electric large regional jet aircraft concept being studied by NASA that leverages advanced propulsion system technologies such as distributed electric propulsion (DEP) and boundary-layer ingestion (BLI) to reduce fuel consumption and emissions. In order to evaluate the individual benefits of these technologies toward the SUSAN Electrofan's wing-mounted propulsion systems, three configurations are proposed.
Preliminary Assessment of a Distributed Electric Propulsion System for the SUSAN ElectrofanAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

Numerical sensitivity to 3 different Voronoi seeding methods is investigated for Large Eddy Simulations (LES). A second order accurate, non-dissipative finite volume discretization is used to systematically investigate the effects of different polyhedral Voronoi mesh types using a sequence of three canonical problems with increasing complexity.
Evaluation of Voronoi Meshes for Large Eddy Simulations of High Lift AerodynamicsAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

NASA is playing an important role in the development of the urban air mobility ecosystem by identifying key research areas and establishing a fleet of conceptual reference vehicles for urban air mobility applications. This paper delves deeper into the study of NASA’s six-passenger tiltwing air taxi aerodynamics using high-fidelity computational fluid dynamics simulations. NASA’s OVERFLOW flow solver has been loosely-coupled with the rotorcraft comprehensive analysis code CAMRAD II.
High-Fidelity Simulations of a Tiltwing Vehicle for Urban Air MobilityAIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023

Research into parachute performance continues to be a source of significant investment from the National Aeronautics and Space Administration to mitigate risks and to enable a variety of exploration missions, including landing on Mars as well as returning to Earth. The cost of flight tests to certify any changes to the current state-of-the-art parachute designs limits the development of next generation parachute systems. Fluid-structure interaction simulations could help accelerate this process once validated.
Fluid-Structure Interaction Simulations of the ASPIRE SR03 Supersonic Parachute Flight Test AIAA SciTech 2023 Forum, National Harbor, MD, January 23-27, 2023