Papers & Reports 2019

Various characteristics of small nominally-orthogonal jets (microjets) located near the trailing edge of an airfoil are investigated as an active aerodynamic load control technology for multi-element high-lift systems. Previously, a microjet circulation control proof of concept study was reported for a microjet modeled as a boundary condition with uniform velocity profile for a given width and location.
Microjet Configuration Sensitivities for Lift Enhancement in High-Lift Systems, AIAA SciTech Forum, San Diego, CA, January 7-11, 2019

This work presents a method to extract sectional line load data from discretized pressure-sensitive paint (PSP) data. PSP is an experimental method to measure full pressure fields on experimental bodies in real time. By extracting sectional load data from these pressure fields, regional comparisons (both quantitative and qualitative) can be made to computational fluid dynamic (CFD) simulations of the same body.
Comparison of SLS Sectional Loads from Pressure-Sensitive Paint and CFD, AIAA SciTech Forum, San Diego, CA, January 7-11, 2019

A methodology is introduced to optimize and extend the inference of pre-entry size, density, strength, and mass of asteroids based on observed light curves. In this development study, a genetic algorithm (GA) approach is coupled with the fragment-cloud model (FCM) to efficiently evaluate entry and breakup for numerous potential asteroid property combinations and determine which case best matches the observed data.
Inference of Meteoroid Characteristics Using a Genetic Algorithm,Icarus, Vol. 329 (September 2019), pp. 270-281

The feasibility of using surface-normal jets near the flap trailing edge as active aerodynamic load control on the two-element airfoil NLR-7301 at a high-lift condition was explored. Using structured curvilinear overset grids and the Reynolds-averaged Navier–Stokes solver, OVERFLOW-2, the two-dimensional flowfield around the airfoil was characterized.
Aerodynamic Load Control for Multi-Element Airfoils Using Surface-Normal Trailing-Edge Blowing,Journal of Aircraft (AIAA), Vol. 56, No. 4, July 2019

Presenation of characteristic summary and updates to the Probabilistic Asteroid Impact Risk Plantary Defence Conference's 2019 Hypothetical Exercise by NASA Ames' Asteroid Thread Assessment Project.
PDC19 Impact Exercise: Probabilistic Asteroid Impact Risk Assessment,International Academy of Astronautics Planetary Defence Conference, College Park, MD, April 29 - May 3, 2019.

In the present 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. (Full paper requires login.)
On the Unsteadiness of Ship Airwakes Subject to Atmospheric Boundary-layer Inflow from a Helicopter Operation Perspective,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

We demonstrate a well-posed formulation of permeable boundary conditions and massflow-rate functionals for adjoint-based mesh refinement and shape optimization governed by the steady Euler equations. The boundary conditions model propulsion-system effects of inlets and nozzles. A two-shock diffuser with an analytic solution is used to verify the implementation. Numerical examples show that the adjoint solution is smooth at the boundary, indicating that the discretization is adjoint consistent when exit pressure is specified at subsonic outflow, and stagnation temperature and pressure at subsonic inflow. (Full paper requires login.)
Adjoint-Based Mesh Adaptation and Shape Optimization for Simulations with Propulsion,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

An ecient strategy for propagating sonic boom signatures from a near-field Computational Fluid Dynamics (CFD) solution to the mid-field is presented. The method is based on a high-order accurate finite-di↵erence discretization of the 3D Euler equations on a specially designed curvilinear grid and a single sweep space marching solution algorithm. The new approach leads to more than a factor of two reduction in overall computational resources compared to the current method used to propagate near-field sonic booms to the ground. (Full paper requires login.)
Efficient Near-Field to Mid-Field Sonic Boom Propagation using a High-Order Space Marching Method,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

A validated computational fluid-structure interaction method for simulating the complex interaction between the large deformation of very thin, highly deformable structures and compressible flows is extended to consider large-scale problems in supersonic flows using parallel computing. The coupled fluid-structure interaction system is solved in a partitioned, or weakly-coupled, manner. (Full paper requires login.)
Fully-Coupled Fluid-Structure Interaction Simulations of a Supersonic Parachute,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

Arc-jets are unique facilities used in research, development, and evaluation of hightemperature thermal protection systems for hypersonic vehicles and planetary entry systems. Thermochemical non-equilibrium computational fluid dynamics simulations have been carried out for the Hypersonic Materials Environmental Test System arc-jet facility to determine the size of a capsule model before arcjet testing by better understanding of the physical phenomena. (Full paper requires login.)
Simulation of HyMETS Flowfield around Baby-SPRITE Entry Probe,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

The accuracy of the scale-resolving simulations for practical geometries strongly depends on the inflow boundary conditions. Imposing experimentally observed turbulent inflow profiles for the numerical simulations is a major challenge. Existing methods available in the literature assume self-similar behavior, which is not true for most of the experiments. In the present work, we formulate the turbulent inflow profile generation technique as an optimization problem. (Full paper requires login.)
A New Recycling Method to Generate Turbulent Inflow Profiles,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

High-fidelity computational fluid dynamics simulations have been carried out in order to analyze the aerodynamics and performance of the side-by-side urban air taxi for urban air mobility. High-order accurate schemes, dual-time stepping, and the delayed detachededdy simulation model have been employed. The flow solver has been loosely coupled with a rotorcraft comprehensive analysis code. (Full paper requires login.)
The Side-by-Side Urban Air Taxi Concept,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

When carbon/phenolic ablators used as spacecraft heatshields are submitted to high temperatures, they undergo a series of irreversible chemical reactions in a process known as pyrolysis. This process has been modeled using different approaches depending on the application field. We compare two pyrolysis models: the traditional devolatilization and the competitive reaction model commonly adopted in the analysis of biomass. (Full paper requires login.)
Comparison Between Traditional and Competitive Reaction Models for the Pyrolysis of High Temperature Aerospace Materials,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

Effects of ducts on coaxial rotors in hover have been studied using a high-fidelity computational fluid dynamics code that solves the three-dimensional unsteady Navier-Stokes equations on overset structured grids. High-order accurate schemes, dual-time stepping, and the delayed detached-eddy simulation model have been employed. (Full paper requires login.)
Simulations of Ducted and Coaxial Rotors for Air Taxi Operations,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

In this study, we have extended our correction method for transonic aerodynamics to baseline and variable camber continuous trailing edge (VCCTEF) geometries of super-critical airfoils at cruise conditions. This correction method modifies Theodorsen theory, which is based on incompressible potential flow over a flat plate. The method is partly based on CFD RANS simulations of oscillating NASA generic transport model (GTM) baseline cruise and VCCTEF airfoil geometries in pitch and shows promise for addressing transonic flutter problems of aeroelasticity. (Full paper requires login.)
Extending A Correction Method for Unsteady Transonic Aerodynamics to Variable Camber Continuous Trailing Edge Flap,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

Laminar-to-turbulent transition of the three-dimensional boundary layer that develops over swept wings is known to be highly sensitive to surface roughness in low-turbulence wind tunnel and flight environments. Numerous studies have been conducted on the effect of discrete and distributed roughness elements, however limited computational effort has been dedicated to the study of transition over swept wings with randomly distributed micron-size roughness. (Full paper requires login.)
Preliminary Scale-Resolving Simulations of Laminar-to-Turbulent Transition in Swept-Wing Flow,AIAA Aviation Forum, Dallas, TX, June 17-21, 2019

The accurate prediction of turbulent mixing in high-pressure turbines that incorporate various airfoil surface-cooling strategies is becoming increasing critical to the design of modern gas turbine engines where the quest for improved efficiency is driving compressor overall pressure ratios and turbine inlet temperatures to much higher levels than ever before. In the present paper, a recently developed computational capability for accurate and efficient scale–resolving simulations of turbomachinery is extended to study the turbulent mixing mechanism of a simplified abstraction of an airfoil trailing-edge cooling slot - a plane wall jet with finite lip thickness discharging into an ambient flow.
Scale–Resolving Simulations of a Fundamental Trailing–Edge Cooling Slot Using a Discontinuous–Galerkin Spectral–Element Method,ASME Turbomachinery Technical Conference & Exposition, Phoenix, AZ, June 17-21, 2019

A higher order computational procedure to alleviate aeroelastic oscillations by using active control surfaces is addressed. Flow is modeled using the high-fidelity Navier–Stokes (NS) equations, compared to the current use of the low-fidelity linear theory to design active controls. An active control module is embedded into a general-purpose NS flow solver developed for full aircraft configurations.
Active Control of Supersonic Transport Aeroelastic Oscillations Using High-Fidelity Equations,IFAC Journal of Systems and Control, Vol. 8, June 30, 2019

Aeroelastic computations are made for a flexible wing with a tip-propeller system designed for electric aircraft. Flow is modeled using the Navier–Stokes equations, and wing structures are modeled using plate finite elements. A time-accurate procedure is developed to embed the flexible wing in an overset grid topology along with rotating blades. Results are validated with existing data from wind-tunnel and potential flow computations.
Dynamic Aeroelasticity of Wings with Tip Propeller by Using Navier–Stokes Equations,AIAA Journal, Vol. 57, No. 8, July 17, 2019

The objective of this paper is to prove for the first time that the entropy split methods based on physical entropies are entropy stable methods for central differencing with SBP operators for both periodic and non-periodic boundary conditions for nonlinear Euler equations.
Entropy Stable Method for the Euler Equations Revisited: Central Differencing via Entropy Splitting and SBP,Journal of Scientific Computing, vol. 81, December 2019

The potential for deflagration to detonation transition (DDT) in an uncontained failure poses extreme risk to nearby personnel. This study performs numerical simulations with detailed chemistry models of confined stoichiometric hydrogen–air mixtures interacting with flow obstructions to better understand the mechanisms of detonation initiation which will inform future risk assessments. Unique obstacle geometries, including both rectangular and curved obstacles, are considered in an effort to isolate important contributors to DDT.
Numerical Investigation of the Effect of Obstacle Shape on Deflagration to Detonation Transition in a Hydrogen-Air Mixture,Combustion and Flame, Vol. 209, August 13, 2019

A new variant of the multilevel Monte Carlo estimator is presented for the estimation of expectation statistics that utilizes sample reuse in specified levels, explicitly removes approximation error bias associated with numerically computed output quantities of interest that have an asymptotic limit behavior, and permits a low variance estimate of the asymptotic rate of convergence to that limit. In addition, it is shown that this new multilevel Monte Carlo variant can yield a computational cost savings.
Multilevel Monte Carlo Estimation of Unbiased Expectation via Sample Reuse and the Low Variance Estimation of Asymptotic Rates,NAS Technical Report NAS-2019-01, NASA Ames Research Center, Moffett Field, CA (PDF 727KB)

A class of high-order nonlinear filter schemes is examined for long-time integrations of computational aeroacoustics (CAA) turbulence applications. This class of schemes was designed for an improved nonlinear stability and accuracy for long-time integration of compressible direct numerical simulation and large eddy simulation computations for both shock-free turbulence and turbulence with shocks.
Skew-symmetric splitting of high-order central schemes with nonlinear filters for computational aeroacoustics turbulence with shocks,Shock Waves, vol. 29, November 2019

Properly assessing the asteroid threat depends on the knowledge of asteroid pre-entry parameters, such as size, velocity, mass, density, and strength. Although a vast number of possible bodies to study exist, such characterization of asteroid populations is currently limited by substantial costs associated with space rendezvous missions and rare meteorite findings.
Using Deep Learning to Automate Inference of Meteoroid Pre-Entry Properties,American Geophysical Union Fall Meeting, San Francisco, CA, December 9-13, 2019

NASA's Digital Transformation (DT) Initiative will dramatically enhance NASA's mission impact by reinventing mission and mission support processes, products, and capabilities, enabled by an innovation culture, digital-savvy workforce, and advanced digital technologies, building on a foundation of modern data management and IT security. This presentation, as part of a conference panel, provides an overview of NASA's DT Initiative, and describes how the Initiative supports an "antidisciplinary" future, where the greatest mission transformation opportunities will be found at the intersections and mergers of multiple disciplines.
NASA’s Digital Transformation (DT) Initiative,American Geophysical Union Fall Meeting, San Francisco, CA, December 9-13, 2019