Papers & Reports 2015

This compendium documents near-field pressure signature measurements and computational predictions made for two low-boom supersonic transport models and five calibration models tested in conjunction with the Lockheed-Martin Aeronautics Company. Sonic boom pressure signatures were measured in the NASA Ames 9 x 7 Supersonic Wind Tunnel at Mach 1.6 and 1.7. The low-boom transport models represent designs for a supersonic transport aircraft anticipated to enter service in the 2020-timeframe. This work supports a NASA challenge to reduce the sonic boom of flight vehicles, and to assess the nozzle plume effects on sonic boom pressure signatures.
Experimental and Computational Sonic Boom Assessment of Lockheed-Martin N+2 Low Boom ModelsNAS Technical Report NAS-2015-01, January 2015, NASA Ames Research Center, Moffett Field, CA.

This paper summarizes an upcoming guide being developed under the auspices of the Joint Army-Navy-NASA-Airforce (JANNAF) Interagency Propulsion Committee to help make critical decisions based on simulation accuracy. In addition to background information, this summary addresses: simulation verification and validation; uncertainty propagation and quantification; and some state-of-the-art approaches for assessing simulation credibility. These approaches are anticipated to be useful to other technical communities conducting physics-based simulations. (Full paper requires login.)
The JANNAF Simulation Credibility Guide on Verification, Uncertainty Propagation and Quantification, and Validation,AIAA Science and Technology Forum and Exposition 2015, Kissimmee, FL, January 2015.

Results are presented for four optimization benchmark problems posed by the AIAA Aerodynamic Design Optimization Discussion Group. The benchmarks involve drag minimization for airfoils and wings, subject to geometric and aerodynamic constraints. Our design approach involves two forms of adaptation. (Full paper requires login.)
Aerodynamic Shape Optimization Benchmarks with Error Control and Automatic Parameterization,AIAA Science and Technology Forum and Exposition 2015, Kissimmee, FL, January 2015.

This paper presents details of Computational Fluid Dynamic modeling of the Space Launch System during ascent. The primary focus of the paper is the flow simulation of the vehicle during ascent using the Overflow Navier-Stokes code. Computations of 739 first-stage flight conditions covering a range of Mach numbers, angles of attack, and roll angles were computed. The overset grid system contained 375 million grid points, and over 28 million CPU hours were used in the simulations. The simulations were run on the Pleiades supercomputer at the NASA Advanced Supercomputer Center at Ames Research Center. (Full paper requires login.)
CFD Simulations of the Space Launch System Ascent Aerodynamics and Booster Separation,AIAA Science and Technology Forum and Exposition 2015, Kissimmee, FL, January 2015.

We present an approach to aerodynamic optimization in which the shape parameterization is progessively and automatically refined. The process consists of an alternating sequence of optimizing within the current search space, and then refining the parameterization to enable the discovery of superior designs. We show that this approach reduces computational cost by optimizing in search spaces of appropriate dimensionality. By automating time-consuming aspects of shape control refinement, it also reduces human cost and dependence on designer expertise. (Full paper requires login.)
Adaptive Shape Control for Aerodynamic DesignAIAA Science and Technology Forum and Exposition 2015, Kissimmee, FL, January 2015.

A higher-order space-time discontinuous Galerkin method is presented for the simulation of compressible flows. The effect of the discrete formulation on the nonlinear stability of the scheme is assessed through numerical simulations. For marginally resolved turbulent simulations at moderate Reynolds number, polynomial dealiasing is shown to be necessary in order to maintain stability at high order. (Full paper requires login.)
Higher-Order Methods for Compressible Turbulent Flows Using Entropy Variables,AIAA Science and Technology Forum and Exposition 2015, Kissimmee, FL, January 2015.

This work assesses the potential aerodynamic performance benefits of a variablecamber, continuous-trailing-edge flap system on a generic transport aircraft at off-design conditions. A process to optimize transport wings while addressing static aeroelastic effects is presented. To establish a proper baseline, a transport wing is first aerodynamically optimized at a mid-cruise flight condition using an inviscid, aeroelastic analysis tool. The optimized wing is then analyzed at off-design cruise conditions. (Full paper requires login.)
Optimized Off-Design Performance of Flexible Wings with Continuous Trailing-Edge Flaps,AIAA Science and Technology Forum and Exposition 2015, Kissimmee, FL, January 2015.

Air-breathing propulsion-assisted flight systems offer the potential for revolutionary change of the space operations paradigm. Horizontal launch of a space-access system provides mission flexibility, responsiveness, and affordability. This paper discusses one way to reduce launch cost by increasing the Mach number at which a launch vehicle is staged from a carrier aircraft. Without exceeding the engine and airframe design limits, the pre-compressor cooling technology allows an operational aircraft to operate at Mach numbers and altitudes beyond its basic operational limits. This is an essential, near-term technology for reducing launch cost to place small-weight payloads in low Earth orbit.
Water Injection Pre-Compressor Cooling Assist Space Access,The Aeronautical Journal, Volume 119, No. 1212, February 2015.

Savors is a visualization framework that supports the ingestion of data streams created by arbitrary command pipelines. Multiple data streams can be shown synchronized by time in the same or different views, which can be arranged in any layout. These capabilities combined with a powerful parallelization mechanism and interaction models already familiar to administrators allows Savors to display complex visualizations of data streamed from many different systems with minimal effort. This paper presents the design and implementation of Savors and provides example use cases that illustrate many of the supported visualization types. (Requires Purchase)
Time-Synchronized Visualization of Arbitrary Data Streams,SPIE Proceedings Vol. 9397: Visualization and Data Analysis 2015, February 8, 2015.

A fast procedure to simulate the unsteady aerodynamic characteristics of a parachute cluster in the vicinity of a capsule is presented. This problem is modeled using a well-validated flow solver, which solves the Reynolds-averaged Navier-Stokes equations for steady and unsteady compressible/incompressible flows about general geometries using an overset grid approach. Results are validated using comparisons with classical theory. The fast generation of a large aerodynamic database is accomplished using the dual-level parallel protocol on a massively parallel supercomputer. (Full paper requires login.)
Fast Database Generation for Parachute Cluster Design Using Navier-Stokes Equations on Supercomputers,23rd AIAA Aerodynamic Decelerator Systems Technology Conference, Daytona Beach, FL, March 30-April 2, 2015.

This report outlines a theoretical approach to adaptive parameterization for aerodynamic optimization of discrete geometries. The motivations for this work include the potential to radically reduce manual setup time and achieve faster and more robust design improvement, especially for problems where many design variables are required. The report provides detailed, practical implementation notes, and contains several verification studies and design examples demonstrating substantial wall-clock time computational savings, smoother shapes, and superior final designs compared to a standard static-parameterization approach. This work is an important step toward greater automation in solving the unfamiliar aerodynamic shape design problems of the future.
Adaptive Shape Parameterization for Aerodynamic Design,NAS Technical Report NAS-2015-02, May 2015, NASA Ames Research Center, Moffett Field, CA.

A novel spectral-element approach for the eikonal equation is presented based on the work of Tucker et al. This approach is readily implemented in standard finite element flow solvers developed for the Navier-Stokes equations. Results are presented for distance function (level set) for three planar configurations: circular cylinder, NACA 0012 airfoil, and T106 airfoil. Results demonstrate that the approach is capable of arbitrary order of accuracy. For configurations with strong convex curvature, additional curvature-based dissipation is added to the eikonal equation to generate a weak solution consistent with the entropy condition. (Full paper requires login.)
Development of a Spectral-Element Approach for the Eikonal Equation,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

Computational simulations using structured overset grids with the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are presented for predicting oblique shock/plume interaction effects to near-field sonic boom signatures. Standard second-order accurate as well as higher-resolution numerical discretizations are utilized and the results are compared with supersonic wind-tunnel data. The cases studied include an empty wind-tunnel at the operating conditions, an isolated shock-generating diamond wedge within the tunnel, and a nozzle with diamond wedge configuration at five different nozzle pressure ratios. (Full paper requires login.)
Numerical Simulations of Shock/Plume Interaction Using Structured Overset Grids,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. (Full paper requires login.)
Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

Results of a computational study carried out to explore the effects of various elastomer configurations joining spanwise contiguous Variable Camber Continuous Trailing Edge Flap (VCCTEF) segments are reported here. This research is carried out as a proof-of-concept study that will seek to push the flight envelope in cruise with drag optimization as the objective. The cruise conditions can be well off design such as caused by environmental conditions, maneuvering, etc. To handle these off-design conditions, flap deflection is used so when the flap is deflected in a given direction, the aircraft angle of attack changes accordingly to maintain a given lift. (Full paper requires login.)
A 3-D Computational Study of a Variable Camber Continuous Trailing Edge Flap (VCCTEF) Spanwise Segment,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

The effect of turbulence models in the off-body grids on the accuracy of solutions for rotor flows in hover has been investigated. Results from the Reynolds-Averaged Navier-Stokes and Laminar Off-Body models are compared. Advection of turbulent eddy viscosity has been studied to find the mechanism leading to inaccurate solutions. A coaxial rotor result is also included. (Full paper requires login.)
Effect of Turbulence Modeling on Hovering Rotor Flows,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

This study focuses on a numerical investigation of a mixing layer vis-a-vis an experimental study using dielectric barrier discharge (DBD) plasma actuators.1 Upstream perturbations from the experiment1−3 are imposed as inflow boundary condition in the direct numerical simulation (DNS) of the mixing layer using a computational methodology reported recently.4,5 Development of the mixing layer is followed computationally through the initial stages of coalescence of vortex structures. This collaborative investigation is unique and has shed some light on the mechanism of the coalescence process of the coherent structures in the mixing layer. (Full paper requires login.)
Mixing Layer: Numerical and Experimental Control Strategies,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

An automatic and efficient method to determine appropriate hole cuts based on distances to the wall and donor stencil maps for overset grids is presented. A new robust procedure is developed to create a closed surface triangulation representation of each geometric component for accurate determination of the minimum hole. Hole boundaries are then displaced away from the tight grid-spacing regions near solid walls to allow grid overlap to occur away from the walls where cell sizes from neighboring grids are more comparable. (Full paper requires login.)
Advances in Distance-Based Hole Cuts on Overset Grids,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

This paper presents details of Computational Fluid Dynamic (CFD) simulations of the Space Launch System during solid-rocket booster separation using the Cart3D inviscid code with comparisons to Overflow viscous CFD results and a wind tunnel test performed at NASA Langley Research Center’s Unitary Plan Wind Tunnel. The Space Launch System (SLS) launch vehicle includes two solid-rocket boosters that burn out before the primary core stage and thus must be discarded during the ascent trajectory. (Full paper requires login.)
Output-Based Adaptive Meshing Applied to Space Launch System Booster Separation Analysis,2015 AIAA Aviation and Aeronautics Forum, Dallas, Texas, June 22-26, 2015.

An independent partial assessment is provided of the technical viability of the Skylon aerospace plane concept, developed by Reaction Engines Limited (REL). The objectives are to verify REL’s engineering estimates of airframe aerodynamics during powered flight and to assess the impact of Synergetic Air-Breathing Rocket Engine (SABRE) plumes on the aft fuselage. The development of an operational reusable launcher from the Skylon concept necessitates the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments.
Skylon Aerodynamics and SABRE Plumes,20th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, Glasgow, Scotland, July 6-9, 2015.

This study presents a performance evaluation for a dual-rail Fourteen Data Rate InfiniBand-connected cluster, where each node has two Intel Xeon E5-2670 (Sandy Bridge) processors and two Intel Xeon Phi coprocessors. The Xeon Phi, based on the Many Integrated Core (MIC) architecture, is of the Knights Corner (KNC) generation. Benchmarks used include the MPI and multi-zone versions of the NAS Parallel Benchmarks. Performance for 4 modes are presented, along with optimization techniques and results for the Weather Research and Forecasting (WRF)n model and OVERFLOW, a general-purpose Navier-Stokes solver for CFD problems.
Early Multi-Node Performance Evaluation of a Knights Corner (KNC) Based NASA Supercomputer,NAS Technical Report NAS-2015-03, NASA Ames Research Center, Moffett Field, CA.

This paper presents the Shift automated transfer tool and the mechanisms it employs to achieve better performance while preserving the stability of HPC environments. Shift encapsulates best practices understood by domain experts during transfers so that scientists can focus on their science without the need to study file transports, resource management, and file systems as well. Shift understands how to utilize the variety of transports that might be deployed throughout a widely distributed user base, how to maximize the performance achievable by each, and the scenarios in which each is most effective. Shift understands which resources are available in a particular HPC environment and how to utilize them for significant performance increases while preventing resource exhaustion. Finally, Shift understands the file systems to which and from which files may be transferred and the nuances to their use that affect performance and stability behind the scenes. (Full paper requires login.)
Automatically Encapsulating HPC Best Practices into Data Transfers,Proceedings of the Second International Workshop on HPC User Support Tools, Article No. 1, Austin, Texas, November 15-15, 2015.

NASA has deployed a 128-node SGI Rackable system where each node has two Intel Xeon E2670 8-core Sandy Bridge processors along with two Xeon Phi 5110P coprocessors. This paper presents preliminary results of a performance evaluation of various aspects of an Intel Xeon Phi-based system. The research team used microbenchmarks to measure the latency and bandwidth of memory and interconnect, I/O rates, and the performance of OpenMP directives and MPI functions. OpenMP and MPI versions of the NAS Parallel Benchmarks were used, along with two production CFD applications, to test 4 programming modes: offload, processor native, coprocessor native and symmetric (processor plus coprocessor).
An Early Performance Evaluation of Many Integrated Core Architecture Based SGI Rackable Computing System,NAS Technical Report NAS-2015-04, NASA Ames Research Center, Moffett Field, CA.

This paper presents a comprehensive performance evaluation of the Pleiades supercomputer’s Intel Xeon E5-2670 8-core Sandy Bridge processor architecture, using low-level benchmarks, NAS Parallel Benchmarks, and four NASA production scientific and engineering applications: OVERFLOW, MITgcm, USM3D, and CART3D. The Sandy Bridge architecture is compared with the system’s earlier-generation Nehalem architecture. Evaluations include the latency and bandwidth of memory and interconnect, hyperthreading, Turbo Boost, Advanced Vector Extensions (AVX), and QPI link rate.
Performance Evaluation of the Intel Sandy Bridge-Based NASA Pleiades Using Scientific and Engineering Application,NAS Technical Report NAS-2015-05, NASA Ames Research Center, Moffett Field, CA

In 2015, 314 users participated in a user survey that addressed 12 NAS/HECC service areas. This report summarizes the survey results and describes activities taken to improve performance in four key areas: job turnaround time, /nobackup filesystems, data transfer, and training.
Results of the 2015 NAS User Survey,Read More