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
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
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
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)
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Notice to Investigators:
When you publish your research based on use of NAS/HECC resources, please acknowledge these in your paper, following the guidelines provided by NASA's High-End Computing Program.
Revisiting the Sun’s Strong Differential Rotation Along Radial Lines
Current state-of-the-art models of the solar convection zone consist of solutions to the Navier-Stokes equations in rotating, 3D spherical shells. Such models are highly sensitive to the choice of boundary conditions. Here we present two suites of simulations differing only in their outer thermal boundary condition, which is either one of fixed-entropy or fixed-entropy-gradient. We find that the resulting differential rotation is markedly different between the two sets.
L. Matilsky, B. Hindman, and J. Toomre
arXiv:2004.00208 [astro-ph.SR], April 1, 2020
TOI-1235 b: A Keystone Super-Earth for Testing Radius Valley Emergence Models Around Early M Dwarfs
Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally-driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/non-rocky transition in period-radius space. Here we present the confirmation of TOI-1235 b, a planet whose size and period are intermediate between the competing model predictions, thus making the system an important test case for emergence models of the rocky/non-rocky transition around early M dwarfs.
R. Cloutier, J. Rodriguez, et al.
arXiv:2004.06682 [astro-ph.EP], April 14, 2020
SCORCH. III. Analytical Models of Reionization with Varying Clumping Factors
In the Simulations and Constructions of the Reionization of Cosmic Hydrogen (SCORCH) project, we compare analytical models of the hydrogen ionization fraction with radiation-hydrodynamic simulations. We derive analytical models of the mass-weighted hydrogen ionization fraction from the local ionization balance equations as a more accurate alternative to the widely adopted model based on the volume filling factor. In particular, our model has a recombination term quadratic in the ionization fraction, which is consistent with the two-body interaction nature of recombination.
N. Chen, A. Doussot, H. Trac, and R. Cen
arXiv:2004.07854 [astro-ph.CO], April 16, 2020
Robustly Detecting Changes in Warm Jupiters’ Transit Impact Parameters
Torques from a mutually inclined perturber can change a transiting planet's impact parameter, resulting in variations in the transit shape and duration. Detection of and upper limits on changes in impact parameter yield valuable constraints on a planetary system's three-dimensional architecture. Constraints for warm Jupiters are particularly interesting because they allow us to test origins theories that invoke a mutually inclined perturber.
R. Dawson
The Astronomical Journal, vol. 159, no. 5, April 22, 2020