Papers & Reports

Recent NAS Papers

An Ultrahot Neptune in the Neptune Desert

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.
J. Jensen, J. Jensen, C. Henze, et al.
Nature Astronomy: Letters, vol. 4, September 14, 2020

Scale Resolving Simulations of the NASA Juncture Flow Model using the LAVA Solver

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. (Full paper requires login.)
A. Ghate, J. Housman, G.-D. Stich, G. Kenway, and C. Kiris
2020 AIAA Aviation Forum (virtual), June 15-19, 2020

Mesh Effects on Flow Solutions for a 2-D Multi-Element Airfoil Using Structured Overset Methods

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. (Full paper requires login.)
A. Chuen and W. Chan
2020 AIAA Aviation Forum (virtual), June 15-19, 2020

ADflow: An Open-Source Computational Fluid Dynamics Solver for Aerodynamic and Multidisciplinary Optimization

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. (Full paper requires login.)
C. Mader, G. Kenway, A. Yildirim, and J. Martins
Journal of Aerospace Information Systems, vol. 17, no. 9, September 2020 (published online June 21, 2020)

Effects of Atmospheric Turbulence Unsteadiness on Ship Airwakes and Helicopter Dynamics

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. (Full paper requires login.)
R. Thedin, S. Murman, J. Horn and S. Schmitz
Journal of Aircraft, vol. 57, no. 3, May 2020 (published online March 17, 2020)

Takeoff Simulation of Lift+Cruise Air Taxi by Using Navier–Stokes Equations

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.
Guru Guruswamy
AIAA Journal, February 17, 2020.

Computational Study of NASA’s Quadrotor Urban Air Taxi Concept

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. (Full paper requires login.)
P. Ventura Diaz and S. Yoon
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Multigrid Preconditioning for a Space-Time Spectral-Element Discontinuous-Galerkin Solver

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. (Full paper requires login.)
M. Franciolini and S. Murman
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

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Development of Unsteady-PSP Data Processing and Analysis Tools for the NASA Ames Unitary 11ft Wind Tunnel

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. (Full paper requires login.)
J. Powell, S. Murman, C. Ngo, N. Roozeboom, D. Murakami, J. Baerny, and J. Li
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Considering Deflection Missions for Asteroid Impact Risk

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. (Full paper requires login.)
C. Rumpf, D. Mathias, L. Wheeler, and J. Dotson
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Analysis of Three Multi-Band Models for Radiative Heat Transfer in LTE Air Plasma

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. (Full paper requires login.)
S. Izquierdo, J. Meurisse, S. Visser, M. Haw, J. Schulz, and N. Mansour
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Preliminary Measurements of the Motion of Arcjet Current Channel Using Inductive Magnetic Probes

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. (Full paper requires login.)
M. Haw, J. Meurisse, S. Visser, S. Izquierdo, J. Schulz, and N. Mansour
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Comparison of Algorithms for High-Order, Metric-Based Mesh Optimization

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. (Full paper requires login.)
D. Sanjaya, K. Fidkowski, and S. Murman
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Reynolds-Averaged Navier-Stokes Computations of the NASA Juncture Flow Model Using FUN3D and OVERFLOW

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. (Full paper requires login.)
C. Rumsey, H. Lee, and T. Pulliam
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design

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. (Full paper requires login.)
D. Maldonado, J. Housman, J. Duensing, J. Jensen, C. Kiris, et al.
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

Effects of Spatial Resolution on Retropropulsion Aerodynamics in an Atmospheric Environment

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. (Full paper requires login.)
A. Korzun, E. Nielsen, A. Walden, W. Jones, J.-R. Carlson, P. Moran, C. Henze, and T. Sandstrom
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

High-Fidelity Numerical Analysis of Arc-Jet Aerothermal Environments

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. (Full paper requires login.)
P. Ventura Diaz, A. Parente, J. Meurisse, S. Yoon, and N. Mansour
2020 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, Orlando, Florida, January 6-10, 2020.

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