Papers and Reports

The NASA Source Diagnostic Test (SDT) campaign experimental data is used for validation of a sliding mesh technique recently implemented within the Launch, Ascent, and Vehicle Aerodynamics computational framework for time-accurate simulation of rotating fans. The far-field acoustics are analyzed in this work, building upon the aerodynamic validation studies previously published in Part I.
Fan Noise Predictions of the NASA Source Diagnostic Test Using Unsteady Simulations With LAVA Part II – Tonal and Broadband Noise Assessment30th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, June 4-7, 2024.

Results from ongoing research on jet noise prediction using wall-modeled large eddy simulations (WMLES) conducted within the Launch Ascent and Vehicle Aerodynamics (LAVA) computational framework are presented. The study primarily focuses on the aeroacoustic implications of multi-stream nozzle configurations with internal mixing generated by the addition of both internal and external plug geometries.
Noise Prediction of Multi-Stream Internally Mixed Jets With External and Internal Pligs Using Large-Eddy Simulation30th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, June 4-7, 2024.

Risk assessment studies of local asteroid hazards traditionally simulate the physics of meteors with engineering models tailored to analyze tens-of-millions of scenarios. However, these simplified approaches still need to solve time-dependent ODEs to model the entry process and the resulting ground damage. To improve computational efficiency, we propose in this paper an orthogonal approach based on machine learning models to predict the size of damaged areas given a list of entry parameters.
Machine Learning for the Prediction of Local Asteroid DamagesActa Astronautica, vol. 219, June 2024.

To create early warning capabilities for upcoming Space Weather disturbances, we have selected a dataset of 61 emerging active regions, which allows us to identify characteristic features in the evolution of acoustic power density to predict continuum intensity emergence. For our study, we have utilized Doppler shift and continuum intensity observations from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO).
Predicting the Emergence of Solar Active Regions Using Machine LearningarXiv:2402.08890 [astro-ph.SR], February 14, 2024.

This paper describes a building-block approach for high-fidelity computational fluid dynamic simulations of NASA’s Lift+Cruise (L+C) Vertical Take-off and Landing (VTOL) concept vehicle. The Reynolds-Averaged Navier-Stokes equations are solved on overset structured grids using OVERFLOW. Overset meshes are generated using recently developed automated meshing tools. A baseline study is initially performed on the vehicle fuselage with wings and tails. Vehicle components such as pylons and gears are then added individually and together to study incremental component aerodynamic effects. Results from this study are also used to demonstrate the capabilities of the automatic meshing tools for performing rapid computational analyses.
Computational Aerodynamic Study of the Lift+Cruise VTOL Concept Vehicle ComponentsTransformative Vertical Flight 2024, Santa Clara, CA, February 6-8, 2024.

This paper discusses the validation of the ascent surface pressure database developed using Computational Fluid Dynamics (CFD) for the Space Launch System (SLS) Program with Artemis I flight data from the ascent phase of flight. The ascent phase begins shortly after the vehicle clears the launch tower and extends to the first staging event. This work compares sensor data from the successful Artemis I flight to point pressures extracted from the implemented surface pressure database for Artemis I and other available CFD data sets.
Validation of SLS Ascent CFD Surface Pressure Databases Using Artemis I Flight DataAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

This paper presents an update to the conceptual design of the NASA Subsonic Single Aft Engine (SUSAN) Electrofan transport aircraft---a 180 passenger, Mach 0.785 hybrid-electric regional jet with an economy range of 750 nmi and a design range of 2,500 nmi. Investigated in this work is the system level sizing and analysis of the SUSAN Electrofan when accounting for system level trades related to its electrified aircraft propulsion (EAP) systems.
Conceptual Design of the Hybrid-Electric Subsonic Single Aft Engine (SUSAN) Electrofan Transport AircraftAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

Wall-modeled large-eddy simulation (WMLES) methods have been used to perform increasingly practical physics based simulations where resolving turbulent structures is important, including those involving the NASA High-Lift Common Research Model geometry. However, the results obtained from these numerical campaigns are typically quite sensitive to choices pertaining to the flux formulation, in addition to the mesh topology and resolution used. The current study seeks to partially alleviate the flux sensitivity by proposing a formulation based on an existing non-dissipative kinetic energy and entropy preserving flux combined with carefully constructed dissipation to achieve stability.
Wall-Modeled Large-Eddy Simulations of a Swept WingAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

The flow past the Boeing Transonic Truss-Braced Wing (TTBW) aircraft is simulated with a Hybrid Reynolds-Averaged Navier-Stokes Large-Eddy Simulations (HRLES) turbulence modeling approach to study transonic buffet onset and evaluate the predictive capability of the numerical approach. All simulations used structured overset curvilinear grids for the free-air configuration, with all simulations performed using the Launch, Ascent, and Vehicle Aerodynamics (LAVA) computational framework.
Simulating Transonic Buffet Aerodynamics for the Boeing Transonic Truss-Braced Wing AircraftAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

A supervised deep learning approach is coupled with heuristic convergence criteria to construct a classification model for detecting the completion (convergence) of computational fluid dynamics (CFD) simulations. Heuristic convergence criteria alone are not always sufficient and more complex decisions are often left to a human analyst. The proposed approach leverages heuristic convergence criteria as well as two deep neural network (DNN) models, one binary and one multi-class, to improve the efficiency and consistency of convergence classification across a wide range of flight regimes.
Deep Neural Network Based Convergence Classification for Computational Fluid DynamicsAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

The development of breakthrough open-rotor propulsion systems that meet performance, fuel efficiency, and noise requirements for commercial viability relies heavily on the availability of reliable and computationally efficient aerodynamic performance and noise prediction tools. This investigation showcases the proficiency of the structured curvilinear overset grid Computational Fluid Dynamics solver implemented in the Launch Ascent and Vehicle Aerodynamics framework for predicting the aerodynamic and aeroacoustic characteristics of a Contra-Rotating Open Rotor propulsion system.
Scale Resolving Simulations of Contra Rotating Open Rotor Noise PredictionAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

A scoping study was conducted on the air supply of a microjet-based active flow control (AFC) system on a twin-turbofan commercial transport airplane. Microjets provide direct lift-control in the linear regime of the lift curve using small surface-normal pneumatic jets located near the trailing edge of a lifting surface such as a wing or flap.
Scoping of an Air Supply System for Active Flow Control on a Commercial Transport AirplaneAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

This work presents a method to generate line loads that are consistent with integrated force and moment constraints, while also following the statistical distribution underlying known line load data. The motivation for this method is to address a particular problem that can arise during the pre-flight analysis of an ascent vehicle. That problem is constructing separate databases, for line loads and integrated aerodynamic coefficients, that contain different data and thus different amounts of quantified uncertainty.
Statistically Consistent Dispersion of Line Loads to Uncertain Integrated Forces and MomentsAIAA SciTech 2024 Forum, Orlando, FL, January 8-12, 2024.

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.