Papers & Reports 2016

The authors exercise the computational fluid dynamics code OVERFLOW on 16 turbulence model validation cases from the NASA Langley Turbulence Model Resource website. This report gives information about the OVERFLOW options used to run these cases, and compares Overflow results with results from other codes and with experiment. The goal is turbulence model validation for Overflow.
OVERFLOW Turbulence Modeling Resource Validation Results,NAS Technical Report NAS-2016-01, NASA Ames Research Center, Moffett Field, CA.

NASA and the U.S. aerospace industry are performing studies of supersonic aircraft concepts with low sonic boom pressure signatures. Computational solutions of flight vehicles are difficult to assess since experimental sonic boom data are without inlet and nozzle exhaust jet effects, and obtained at significantly lower Reynolds numbers. A large number of high-fidelity numerical simulations of a variety of shock generators were evaluated to define a reduced collection of five suitable test models. The computational results of the candidate wind tunnel test models as they evolved are summarized, and pretest computations of the final designs are provided. (Full paper requires login.)
Wind Tunnel Model Design for Sonic Boom Studies of Nozzle Jet Flows with Shock Interactions,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

Reliable noise prediction capabilities are essential to enable novel fuel efficient open rotor designs that can meet the community and cabin noise standards. Toward this end, immersed boundary methods have reached a level of maturity where more and more complex flow problems can be tackled with this approach. This paper demonstrates that our higher-order immersed boundary method provides the ability for aeroacoustic analysis of wake-dominated flow fields generated by a contra-rotating open rotor. (Full paper requires login.)
Open Rotor Computational Aeroacoustic Analysis with an Immersed Boundary Method,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

As they decelerate through the atmosphere, meteors transfer mass, momentum and energy into the surrounding air at tremendous rates. The entry of such bolides produces strong blast waves that can propagate hundreds of kilometers and cause substantial terrestrial damage even when no ground impact occurs. We develop a new technique for meteoroid airburst modeling based upon conservation analysis for the deposition of mass, momentum and energy. (Full paper requires login.)
Numerical Simulation of Bolide Entry with Ground Footprint Prediction,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

The development of the aerodynamic database for the Space Launch System (SLS) booster separation environment has presented many challenges because of the complex physics of the flow around three independent bodies due to proximity effects and jet interactions from the booster separation motors and the core stage engines. This aerodynamic environment is difficult to simulate in a wind tunnel experiment and also difficult to simulate with computational fluid dynamics. (Full paper requires login.)
Space Launch System Booster Separation Aerodynamic Database Development and Uncertainty Quantification,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

Wind tunnel tests of a 5.75% scale model of the Boeing Hybrid Wing Body (HWB) configuration were conducted in the NASA Langley Research Center (LaRC) 14’x22’ and NASA Ames Research Center (ARC) 40’x80’ low speed wind tunnels as part of the NASA Environmentally Responsible Aviation (ERA) Project. Computational fluid dynamics (CFD) simulations of the flow-through nacelle (FTN) configuration of this model were performed before and after the testing. This paper presents a summary of the experimental and CFD results for the model in the cruise and landing configurations. (Full paper requires login.)
NASA Environmentally Responsible Aviation Hybrid Wing Body Flow-Through Nacelle Wind Tunnel CFD,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

Pressure Sensitive Paint (PSP) is an optical technique commonly used in the aerospace industry to measure time-averaged pressure on a wind tunnel model. A new challenge is the development and use of PSP for dynamic pressure fluctuations to study unsteady flow phenomena. The work presented in this paper is a small-scale, risk-reduction test performed at NASA Ames Research Center’s Fluid Mechanics Lab to investigate the use of unsteady PSP (uPSP) and to compare against familiar unsteady pressure transducer data. (Full paper requires login.)
Unsteady PSP Measurements on a Flat Plate Subject to Vortex Shedding from a Rectangular Prism,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

Interactional aerodynamics of multi-rotor flows has been studied for a quadcopter representing a generic quad tilt-rotor aircraft in hover. The objective of the present study is to investigate the effects of the separation distances between rotors, and also fuselage and wings on the performance and efficiency of multirotor systems. Three-dimensional unsteady Navier-Stokes equations are solved using a spatially 5th order accurate scheme, dual-time stepping, and the Detached Eddy Simulation turbulence model. (Full paper requires login.)
Computational Analysis of Multi-Rotor Flows,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

Computational simulations using structured overlapping grids with the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are presented for predicting tonal noise generated by a contra-rotating open rotor (CROR) propulsion system. A coupled Computational Fluid Dynamics (CFD) and Computational AeroAcoustics (CAA) numerical approach is applied. (Full paper requires login.)
Structured Overlapping Grid Simulations of Contra-Rotating Open Rotor Noise,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

Detached-eddy simulations of unsteady buffet in the transonic regime about a hammerhead payload fairing using the OVERFLOW solver are presented. The computed results are compared to mean and unsteady pressures measured by Coe and Nute. Details of the transonic flow physics provide understanding in regions where the simulation and experimental results mismatch. Spectral and proper orthogonal decompositions of the unsteady surface pressure field are presented to further aid the analysis. A sensitivity study for temporal resolution, spatial operator, and turbulence model is included. (Full paper requires login.)
Simulation of a Hammerhead Payload Fairing in the Transonic Regime,54th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, San Diego, CA, January 4-8, 2016.

The Skylon concept incorporates the highly innovative synergetic air-breathing rocket engine concept that has the potential to revolutionize the mode of propulsion for transportation of medium-weight payloads to low Earth orbits. An independent partial assessment is provided of the technical viability of the Skylon concept. (Full paper requires login.)
Skylon Aerospace Plane and Its Aerodynamics and Plumes,Journal of Spacecraft and Rockets (AIAA), February 26, 2016.

An introduction to the Launch Ascent and Vehicle Aerodynamics (LAVA) framework, developed at NASA Ames Research Center. The solver combines computational fluid dynamics capabilities with auxiliary modules, such as conjugate heat transfer and computational aero-acoustics. Several NASA mission-related applications are presented to demonstrate the capabilities for large-scale applications. Two validation cases related to NASA aeronautics applications are also presented: the 1st AIAA Sonic Boom Prediction Workshop test cases and a computational study of slat noise. (Full paper requires login.)
Computational Framework for Launch, Ascent, and Vehicle Aerodynamics (LAVA),Aerospace Science and Technology, Vol. 55, August 2016.

Computational aeroacoustic simulations using the structured overset grid approach and higher-order finite difference methods within the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are presented for slat noise predictions. The simulations are part of a collaborative study comparing noise generation mechanisms between a conventional slat and a Krueger leading edge flap. Simulation results are compared with experimental data acquired during an aeroacoustic test in the NASA Langley Quiet Flow Facility. Details of the structured overset grid, numerical discretization, and turbulence model are provided. (Full paper requires login.)
Slat Noise Predictions using Higher-Order Finite-Difference Methods on Overset Grids,22nd AIAA/CEAS Aeroacoustics Conference, Lyon, France, May 30 - June 1, 2016.

In this study, we demonstrate the design of a Krueger flap as a substitute for a conventional slat in a high-lift system. This notional design, with the objective of matching equivalent-mission performance on aircraft approach, was required for a comparative aeroacoustic study with computational and experimental components. We generated a family of high-lift systems with Krueger flaps based on a set of design parameters. Then, we evaluated the high-lift systems using steady 2D RANS simulations to find a good match for the conventional slat, based on total lift coefficients in free-air. (Full paper requires login.)
Computational Design of a Krueger Flap Targeting Conventional Slat Aerodynamics,22nd AIAA/CEAS Aeroacoustics Conference, Lyon, France, May 30 - June 1, 2016.

The NASA Generic Transport Model (GTM) aircraft with flexible wing and Variable Camber Continuous Trailing Edge Flap (VCCTEF) system is analyzed at different stages of cruise flight by means of a static aeroelastic model. The model couples a single beam finite element model to aerodynamic loads obtained with the Cart3D Euler solver. A Matlab framework is used to steer the angle of attack of the deformed wing to realize the required lift. Viscous simulations are performed on the same configurations using the Launch Ascent and Vehicle Aerodynamics (LAVA) curvilinear RANS solver at matching lift coefficient. (Full paper requires login.)
Comparison of Viscous and Inviscid Loads in a Static Aeroelastic Model of the Variable Camber Continuous Trailing Edge Flap Concept in the Transonic Regime,AIAA Aviation Forum, Washington D.C., June 13-17, 2016.

This paper reports a detailed computational high-lift study of the Variable Camber Continuous Trailing Edge Flap (VCCTEF) system carried out to explore the best VCCTEF designs, in conjunction with a leading edge flap called the Variable Camber Krueger (VCK), for take-off and landing. For this purpose, a three-segment variable camber airfoil employed as a performance adaptive aeroelastic wing shaping control effector for a NASA Generic Transport Model (GTM) in landing and take-off configurations is considered. (Full paper requires login.)
Lift Optimization Study of a Multi-Element Three-Segment Variable Camber Airfoil,AIAA Aviation Forum, Washington D.C., June 13-17, 2016.

An immersed boundary method for the compressible Navier-Stokes equation and the additional infrastructure that is needed to solve moving boundary and fully coupled fluid-structure interaction problems is described. All the methods described in this paper were implemented in NASA’s Launch Ascent and Vehicle Aerodynamics solver framework. The underlying immersed boundary method is based on the locally stabilized immersed boundary method that was previously introduced by the authors. (Full paper requires login.)
An Immersed Boundary Method for Solving the Compressible Navier-Stokes Equations with Fluid-Structure Interaction,AIAA Aviation Forum, Washington D.C., June 13-17, 2016.

The linear stability of implicit time integration using dual-time stepping is analyzed for several temporal schemes. We show that the inner iterations in pseudo-time introduce a secondary convergence criterion to the numerical method. The equations governing the evolution of the amplification factor in pseudo-time are derived and analyzed to determine whether the implicit scheme’s stability properties in physical time are compromised by partial convergence of the unsteady residual. (Full paper requires login.)
Stability Analysis of Dual-Time Stepping,AIAA Aviation Forum, Washington D.C., June 13-17, 2016.

NASA is the curator and host for large quantities of observation and simulation data. By some estimates, NASA’s approximately 100 current active missions, observing Earth, the solar system and deep space, produce more than 50 PBs of data annually. Similarly, large-scale simulations run on its supercomputers are starting to produce terabytes and sometimes petabytes of data from each run. As NASA’s flagship site for computational science and engineering at scale, the NASA Advanced Supercomputing (NAS) Division, supports a user base that is at the forefront of data intensive and data driven science. Our users’ codes utilize and generate very large datasets and analyzing these datasets to extract information and knowledge is a fundamental part of their workflows.
Merging Big Data and HPC for Large-Scale Analysis/Analytics at the NASA Advanced Supercomputing (NAS) Division,Big Data and Extreme-Scale Computing, Frankfurt, Germany, June 15-17, 2016.

To simulate turbulent eddies, initial and interface flow fields need to be synthesized consistent with the algorithm being employed. In this report, the turbulent kinetic energy conservation issue is discussed followed by a presentation of the detailed steps to synthesize an initial flow field for computing turbulent eddies.
On Generation of Synthetic Initial Flow Field for Simulating Turbulent Eddies,NAS Technical Report NAS-2016-02, NASA Ames Research Center, Moffett Field, CA.

Monitoring and understanding climate-induced changes in the boreal and arctic vegetation is critical to aid in prognosticating their future. We used a 33 year (1982–2014) long record of satellite observations to robustly assess changes in metrics of growing season (onset: SOS, end: EOS and length: LOS) and seasonal total gross primary productivity. Particular attention was paid to evaluating the accuracy of these metrics by comparing them to multiple independent direct and indirect growing season and productivity measures.
Changes in Growing Season Duration and Productivity of Northern Vegetation Inferred from Long-Term Remote Sensing Data,Environmental Research Letters, Vol. 11, No. 8, July 27, 2016.

Authors present a unique platform for molecular visualization and design that uses novel subatomic feature detection software in tandem with 3D hyperwall visualization technology. The fleshing-out of pharmacophores in drug molecules, as well as reactive sites in catalysts, focusing on subatomic features, is demonstrated. (Full paper requires login.)
Volume-Rendering on a 3D hyperwall: A Molecular Visualization Platform for Research, Education, and Outreach,Journal of Molecular Graphics and Modeling, Vol. 70, November 2016.

An efficient process to aerodynamically optimize transport wings while addressing static aeroelastic effects is presented. The process is used to assess the aerodynamic performance benefits of a full-span trailing-edge flap system on a generic transport aircraft at off-design conditions. Results indicate that the flap system allows for significant improvement in performance throughout cruise and that it can be advantageous even for wings with increased flexibility. (Full paper requires login.)
Optimization of Flexible Wings with Distributed Flaps at Off-Design Conditions,Journal of Aircraft, Vol. 53, No. 6 (2016), November-December 2016.

This paper describes dynamic stability analysis performed for a typical, future hypersonic transport vehicle during atmospheric flight. Unsteady aerodynamic data in the form of indicial responses are generated by solving the Navier–Stokes equations. Computations needed at multiple Mach numbers and associated angles of attack are computed in a single job by using dual-level parallel script. Validity of the indicial approach is established by comparing results with experiment and the time-integration method. Flutter boundaries associated with pitch and heave rigid-body degrees of freedom are computed. The effect of the position of the mass center on flutter boundaries, which is more predominant in the transonic regime, is shown. This work advances stability analysis procedures for next-generation hypersonic vehicles.
Dynamic Stability Analysis of Hypersonic Transport During Reentry,AIAA Journal, Vol. 54, No. 11, November 2016.

This collaborative NASA and Joint Army-Navy-NASA-Air Force (JANNAF) Interagency Propulsion Committee publication presents a compilation of some key advances in the processes for establishing the credibility of numerical simulation over the last 10 years, specifically in the discipline of continuum physics.
Simulation Credibility: Advances in Verification, Validation, and Uncertainty Quantification,NASA/TP—2016-219422, NASA Ames Research Center, Moffett Field, CA.