Papers & Reports 2018

The High-Lift Common Research Model (HL-CRM) and the JAXA Standard Model (JSM) were analyzed computationally using both the OVERFLOW and LAVA codes for the third AIAA High-Lift Prediction Workshop. Geometry descriptions and the test cases simulated are described. With the HL-CRM, the effects of surface smoothness during grid projection and the effect of partially sealing a flap gap were studied. Grid refinement studies were performed at two angles of attack using both codes. (Full paper requires login.)
Contributions to HiLiftPW-3 Using Structured, Overset Grid Methods,2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Kissimmee, Florida, January 8-12, 2018.

High-fidelity Computational Fluid Dynamics (CFD) simulations have been carried out for several multi-rotor Unmanned Aerial Vehicles (UAVs). Three vehicles have been studied: the classic quadcopter DJI Phantom 3, an unconventional quadcopter specialized for forward flight, the SUI Endurance, and an innovative concept for Urban Air Mobility (UAM), the Elytron 4S UAV. The three-dimensional unsteady Navier-Stokes equations are solved on overset grids using high-order accurate schemes, dual-time stepping, and a hybrid turbulence model.
High-Fidelity Computational Aerodynamics of Multi-Rotor Unmanned Aerial Vehicle,2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Kissimmee, Florida, January 8-12, 2018.

Boundary conditions appropriate for simulating flow entering or exiting the computational domain to mimic propulsion effects have been implemented in an adaptive Cartesian simulation package. A robust iterative algorithm to control mass flow rate through an outflow boundary surface is presented, along with a formulation to explicitly specify mass flow rate through an inflow boundary surface. The boundary conditions have been applied within a mesh adaptation framework based on the method of adjoint-weighted residuals. (Full paper requires login.)
Formulation and Implementation of Inflow/Outflow Boundary Conditions to Simulate Propulsive Effects,2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Kissimmee, Florida, January 8-12, 2018.

This paper presents a summary of the performance of three CFD codes; OpenFOAM, STAR-CCM+ and LAVA using unstructured grids for the third AIAA High-Lift prediction workshop. Three test-cases were computed; a 2D DSMA661 airfoil, the NASA high-lift Common-Research Model (CRM) and the JAXA Standard Model (JSM) high-lift model. Each solver used a choice among several turbulence models including the Spalart-Allmaras, SST and the k − ε lag elliptic blending model. (Full paper requires login.)
3rd High-Lift Workshop Summary Paper - OpenFOAM, STAR-CCM+ & LAVA Simulations on Unstructured Grids,2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Kissimmee, Florida, January 8-12, 2018.

We explore the feasibility of using nominally-orthogonal jets as active aerodynamic load control for multi-element high-lift systems, and whether the nominally-orthogonal jets can offer a variety of performance improvements. These nominally-orthogonal jets inject momentum normal to the airfoil surface near the flap trailing edge, where they create a vortex that entrains flow from the opposing side and change the airfoil circulation. Lift-enhancement opportunities of trailing edge nominally-orthogonal jets have previously been studied by Malavard et al. and Blaylock et al. on single-element airfoils; however, their effect on drag was not thoroughly investigated. In this study, we investigate two-dimensional nominally-orthogonal jet effects on both lift and drag on a two-element airfoil, NLR7301. (Full paper requires login.)
Computational Investigation of Nominally-Orthogonal Pneumatic Active Flow Control for High-Lift Systems,2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Kissimmee, Florida, January 8-12, 2018.

In response to the 3rd AIAA CFD High Lift Prediction Workshop, the workshop cases were analyzed using Reynolds-averaged Navier-Stokes flow solvers within the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework. For the workshop cases the advantages and limitations of both overset-structured an unstructured polyhedral meshes were assessed. The workshop included 3 cases: a 2D airfoil validation case, a mesh convergence study using the High Lift Common Research Model, and a nacelle/pylon integration study using the JAXA Standard Model. (Full paper requires login.)
LAVA Simulations for the 3rd AIAA CFD High Lift Prediction Workshop with Body Fitted Grids,2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Kissimmee, Florida, January 8-12, 2018.

We have empirically estimated how often fireball shocks produce overpressure at the ground sufficient to damage windows. Our study used a numerical entry model to estimate the energy deposition and shock production for a suite of 23 energetic fireballs reported by US Government sensors over the last quarter century. For each of these events we estimated the peak overpressure on the ground and the ground area above overpressure thresholds of 200 and 500 Pa where light and heavy window damage, respectively, is expected. Our results suggest that at the highest overpressure it is the rare, large fireballs (such as the Chelyabinsk fireball) which dominate the long-term areal ground footprints for heavy window damage.
The Frequency of Window Damage Caused by Bolide Airbursts: A Quarter Century Case Study,arXiv:1802.07299v1 [astro-ph.EP], February 20, 2018.

In the study, HECC’s Application Performance and Productivity team used a combination of the NAS Parallel Benchmarks and six full applications from NASA’s workload on Pleiades and Electra to compare performance of nodes based on three different generations of Intel Xeon processors—Haswell, Broadwell, and Skylake. Because of export control limitations, the most heavily used applications on Pleiades and Electra could not be used in the cloud; therefore, only one of the applications, OpenFOAM, represents work from the Aeronautics Research Mission Directorate and the Human and Exploration Mission Directorate. The other five applications are from the Science Mission Directorate.
Evaluating the Suitability of Commercial Clouds for NASA’s High Performance Computing Applications: A Trade Study,NAS Technical Report NAS-2018-01, NASA Ames Research Center, Moffett Field, CA.

The results of a layout trade study of a full-span, trailing-edge flap system for the NASA Common Research Model are presented. Previously developed analysis and design tools are used to determine the potential performance benefits of several flap layouts on a highly flexible version of the aircraft wing. The wing is first re-twisted for optimal aerodynamic performance at the design cruise condition while addressing aeroelastic effects. Several flap layouts are then installed on the new baseline wing. (Full paper requires login.)
Distributed-Flap Layout Trade Study on a Highly Flexible Common Research Model,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

A previously developed space-time conservative blade element body-force rotor model coupled to a Cartesian Euler solver is extended to simulate rotors and low Reynolds number propellers in forward flight. Stall delay is shown to be an important factor in hover and axial flight, and we show that airfoil tables that include Reynolds number effects enable accurate and efficient performance predictions for APC Thin Electric 10 inch diameter propellers, requiring less than 10 minutes per case on a modern workstation. (Full paper requires login.)
Efficient Simulation of Multi-rotor Vehicles with Low Reynolds Number Propellers,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

This paper reports high-lift study results of a two-element Variable Camber Continuous Trailing Edge Flap (VCCTEF) and a leading edge flap called the Variable Camber Krueger (VCK) system. The present study follows an earlier three-element study of a VCK-VCCTEF system with a fowler slot. The three-element system is typically found on the inboard section of the considered wing and the two-element system on the outboard section. The present high lift study in conjunction with the earlier companion study characterizes the aerodynamic state of the system in take-off and landing configurations. (Full paper requires login.)
Lift Characterization Study of a Two-Element Three-Segment Variable Camber Airfoil,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

This paper presents a method for adjusting sectional loads to match target values for integrated force and moment coefficients. In a typical application, the sectional load profile for one flight condition is calculated from Computational Fluid Dynamics (CFD) while the integrated forces and moments are measured in a wind tunnel experiment. These two methods do not generally result in identical redictions, and this leads to an inherent inconsistency between different data products. This paper aims to provide a procedure to remove that inconsistency. (Full paper requires login.)
Adjustments and Uncertainty Quantification for SLS Aerodynamic Sectional Loads,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

A study of the implementation of the Amplification Factor Transport (AFT) laminar-turbulent transition model in the Launch Ascent and Vehicle Aerodynamics (LAVA) solver is presented. As part of the verification and validation phase, a range of configurations is considered, including a 2D flat plate, the wind-turbine airfoil S809 and the Natural-Laminar-Flow airfoil for general aviation applications NLF(1)-0416. (Full paper requires login.)
Implementation and Assessment of the Amplification Factor Transport Laminar-Turbulent Transition Model,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

Understanding spatial development of a turbulent mixing layer is essential for various aerospace applications. However, multiple factors affect physics of this flow, making it difficult to reproduce results of experiments in simulations. The current study investigates sensitivity of direct numerical simulation (DNS) of such a flow to computational parameters. In particular, effects of a time step in a temporal discretization scheme, dimensions of the computational domain, and the laminar boundary layer characteristics at the splitter plate trailing edge are considered. (Full paper requires login.)
Analysis of Uncertainty Sources in DNS of a Turbulent Mixing Layer using Nek5000,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

Lattice Boltzmann (LB) based Large Eddy Simulation (LES), Reynolds-averaged Navier-Stokes (RANS) as well as hybrid RANS/LES methods within the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are applied to NASA’s wall-mounted hump. Computational results are compared with experiments performed by Greenblatt, et al. A detailed comparison between the accuracy and resolution requirements of the two approaches for turbulence resolving simulations, as well as the suitability of different grid paradigms (body-fitted curvilinear and block structured Cartesian) are presented. (Full paper requires login.)
Application of Lattice Boltzmann and Navier-Stokes Methods to NASA’s Wall Mounted Hump,2018 AIAA Aviation Forum, Atlanta, Georgia, June 25-29, 2018.

We report the results of a search for candidate Li-rich giants among 569,738 stars of the SDSS DR10 dataset. With small variations, our approach is based on that taken in an earlier search for EMP/CEMP stars and uses the same dataset. By taking carefully selected cuts in a multidimensional phase space, we isolate a sample of potential Li-rich giant stars. From these, using detailed comparison with dwarf and giant MILES stars, and our own individual spectral classifications, we identify a set of high likelihood candidate Li-rich giant stars.
A Search for Candidate Li-Rich Giant Stars in SDSS DR10,arXiv:1806.10295 [astro-ph.SR], June 27, 2018.

Asteroids populations are highly diverse, ranging from coherent monoliths to loosely bound rubble piles, with a broad range of material and compositional properties. These different structures and properties could significantly affect how an asteroid breaks up and deposits energy in the atmosphere, and how much ground damage may occur from resulting blast waves. We have previously developed a fragment-cloud model (FCM) for assessing the atmospheric breakup and energy deposition of asteroids striking Earth. The approach represents ranges of breakup characteristics by combining progressive fragmentation with releases of variable fractions of debris and larger discrete fragments. In this work, we have extended the FCM to also represent asteroids with varied initial structures, such as rubble piles or fractured bodies. (Full paper requires login.)
Atmospheric Energy Deposition Modeling and Inference for Varied Meteoroid Structures,Icarus, vol. 315, November 15, 2018.

Assuring stability of supersonic aircraft, particularly during descent from the supersonic Mach regime to the transonic regime, is important. An aircraft can deviate from its normal descent trajectory due to coupling between flows and rigid-body motions. One such possibility is an aircraft experiencing phugoid oscillations. In this paper, the trajectory equations associated with phugoid motion are integrated with RANS equations, and results are demonstrated for a supersonic transport aircraft.
Phugoid Motion Simulation of a Supersonic Transport Using Navier-Stokes Equations,AIAA Journal, Technical Notes, Vol. 56, No. 6, June 2018.

The Wide-Field Infrared Survey Telescope (WFIRST) is planned to have a coronagraphic instrument (CGI) to enable high-contrast direct imaging of exoplanets around nearby stars. The majority of nearby FGK stars are located in multi-star systems, including the Alpha Centauri stars which may represent the best quality targets for the CGI on account of their proximity and brightness potentially allowing the direct imaging of rocky planets. However, a binary system exhibits additional leakage from the off-axis companion star that may be brighter than the target exoplanet. Multi-Star Wavefront Control (MSWC) is a wavefront-control technique that allows suppression of starlight of both stars in a binary system thus enabling direct imaging of circumstellar planets in binary star systems such as Alpha Centauri. We explore the capabilities of the WFIRST CGI instrument to directly image multi-star systems using MSWC. (Full paper requires login.)
Multi-Star Wavefront Control for the Wide-Field Infrared Survey Telescope Coronagraph Instrument,SPIE Astronomical Telescopes + Instrumentation, Austin, Texas, June 10-15, 2018.

Current high-contrast imaging systems implement wavefront control using traditional deformable mirrors developed for atmospheric turbulence correction, which require large strokes, high-speed, and continuous phase correction. However, high-contrast imaging has different requirements. Thus, developing a specialized deformable mirror for this application able to meet the demanding requirements of future exoplanet imaging flagship missions is valuable for the exoplanet scientific community. In this paper, we propose a novel wavefront control approach, called Sparse Wave-Front Control (SWFC), which enables high-contrast imaging using sparse phase changes on the active surface re-directing coherent starlight to null speckles. (Full paper requires login.)
Sparse Wavefront Control: A New Approach to High-Contrast Imaging,SPIE Astronomical Telescopes + Instrumentation, Austin, Texas, June 10-15, 2018.

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.
Validation of WMLES on a Periodic Channel Flow Featuring Adverse/Favorable Pressure Gradients,Tenth International Conference on Computational Fluid Dynamics (ICCFD10), Barcelona, Spain, July 9-13, 2018.

Time-dependent Reynolds-averaged Navier-Stokes simulations have been carried out for a NACA 0012 airfoil and a flexible UH-60A rotor undergoing dynamic stall. The OVERFLOW computational fluid dynamics (CFD) code is used to explore the use of near-body adaptive mesh refinement (NB-AMR) for the first time on a flexible helicopter rotor in forward flight. Emphasis is placed on understanding the temporal and spatial convergence of the solutions, their numerical efficiency and stability, and establishing a grid-converged solution.
Numerical Simulation of Dynamic Stall Using Near-Body Adaptive Mesh Refinement,Tenth International Conference on Computational Fluid Dynamics (ICCFD10), Barcelona, Spain, July 9-13, 2018.

Performance enhancements in NASA’s recently developed Lattice Boltzmann solver within the Launch Ascent and Vehicle Aerodynamics (LAVA) framework are presented. Two key algorithmic developments are highlighted. A coarse-fine interface treatment that discretely conserves mass and momentum has been implemented and successfully verified and validated. Code optimizations targeting improved serial and parallel performance were presented. For a simple turbulent Taylor-Green Vortex problem, we were able to demonstrate a 2.3x speedup over the baseline code for a single Skylake-SP node containing 40 physical cores, and a 2.14x speedup for 64 nodes containing 2560 physical cores.
Performance Enhancements for the Lattice-Boltzmann Solver in the LAVA Framework,Tenth International Conference on Computational Fluid Dynamics (ICCFD10), Barcelona, Spain, July 9-13, 2018.

Starting with a Boundary Representation (BRep) of the geometry of an aerospace vehicle, an automated marching scheme is presented for generation of structured overset surface meshes. First, a pre-processing step automatically generates discrete representations of the BRep faces and BRep edges by tessellating in parameter space. Topological connectivity between the discretized BRep edges is then established, followed by automatic grid point distribution on these edges based on local turning angle, proximity to sharp geometric features, and prescribed maximum stretching ratio and grid spacing.
An Automated Marching Scheme for Overset Structured Surface Mesh Generation,Tenth International Conference on Computational Fluid Dynamics (ICCFD10), Barcelona, Spain, July 9-13, 2018.

There is renewed interest in developing new supersonic transports after the discontinuation of the Concorde supersonic jet, which was mostly limited for flights over transoceanic routes due to the severe noise of the sonic boom. To avoid the sonic boom, more slender configurations, such as the Low Boom Flight Demonstrator configuration, are being considered; or unconventional configurations, such as aircraft with forward swept wings, the short-period oscillation (SPO) has been found to significantly impact the aeroelastic response. In this Note, the effect of SPO on aeroelastic responses of a typical supersonic transport is studied. (Full paper requires login.)
Navier–Stokes Equations-Based Aeroelasticity of Supersonic Transport Including Short-Period Oscillations,AIAA Journal, Technical Notes, Vol. 56, No. 8, August 2018.

A wide range of meteors were simulated impacting Earth's atmosphere using the ALE3D hydrocode. The size, density, strength curve, entry angle, and velocity of the meteors were varied to cover the parameter space of airbursts of interest to planetary defense in general which encompasses the Tunguska event in particular. The hydrocode simulations were used to calibrate a simple analytical model that can be used to quickly estimate the burst height of an incoming asteroid or comet.
Hydrocode Simulations of Asteroid Airbursts and Constraints for Tunguska,Icarus, vol. 327, July 15, 2019.

A mathematical procedure is presented for the calculation of exact cumulative distribution statistics for a viscosity-free variant of Burgers nonlinear partial differential equation (PDE) in one space dimension and time subject to sinusoidal initial data with uncertain (random variable) amplitude or phase shift. Analytical solutions of nonlinear PDEs with uncertain initial and/or boundary data are invaluablebenchmarks in assessing approximate uncertainty quantification techniques. Mathematical proofs are provided to verify that exact cumulative distribution statistics can be systematically and robustly obtained for all forward time.
On the Calculation of Exact Cumulative Distribution Statistics for Burgers Equation,NASA Technical Publication—2018-220040, NASA Ames Research Center, November 2018.

Here we present a flexible tensor network based simulator for quantum circuits on different topologies, including the Google Bristlecone QPU. Our simulator can compute both exact amplitudes, a task essential for the verification of the quantum hardware, as well as low-fidelity amplitudes to mimic Noisy Intermediate-Scale Quantum (NISQ) devices. Our analysis is supported by extensive simulations on NASA HPC clusters Pleiades and Electra.
A Flexible High-Performance Simulator for the Verification and Benchmarking of Quantum Circuits Implemented on Real Hardware,arXiv:1811.09599v3 [quant-ph], October 10, 2019.

The Tunguska meteor airburst has been extensively studied and modeled in attempts to deduce its size, properties, and impact characteristics. However, most of the existing modeling and simulation studies have investigated a small subset of cases based on assumptions of representative densities, velocities, or other properties. In this study, we use a probabilistic asteroid impact risk model to assess the entry, burst, and ground damage from 50 million Tunguska-scale asteroid impacts, covering a full range of potential impactor properties. The impact cases are sampled from probabilistic distributions representing our current knowledge of asteroid properties, entry trajectories, and size frequencies.
Probabilistic Assessment of Tunguska-Scale Asteroid Impacts,Icarus, Volume 327, July 15, 2019.

Assessments of the risk posed by asteroid impacts depend implicitly upon estimates of how frequently asteroids of different sizes and properties are expected to strike Earth. These impact rates are generally based upon populations of near-Earth objects as a function of absolute magnitude, which are then translated to equivalent size frequencies by assuming an average albedo. However, this simplified approach neglects the broad distribution of sizes and properties among objects of a given absolute magnitude. In this study, we use a probabilistic asteroid impact risk model to more rigorously investigate the effects of asteroid property distributions on estimated impact rates as a function of diameter, energy, mass, and blast damage radius.
Effects of Asteroid Property Distributions on Expected Impact Rates,Icarus, Volume 321, March 15, 2019.