Papers & Reports 2014

The Launch Ascent and Vehicle Aerodynamics (LAVA) solver, developed at NASA Ames Research Center, is introduced. The solver focuses on Computational Fluid Dynamics (CFD), but also features auxiliary modules for Conjugate Heat Transfer (CHT) and Computational Aero-Acoustics (CAA) capabilities. The LAVA framework is designed to be grid-agnostic; it can handle Cartesian block-structured curvilinear or unstructured grids either in stand-alone or by coupling different grid types through an overset interface. (Full paper requires login).
The LAVA Computational Fluid Dynamics Solver,52nd Aerospace Sciences Meeting, AIAA 2014-0558, National Harbor, MD, January 13-17, 2014.

The Overflow viscous overset solver with an actuator-disk propulsor model is used to simulate the flow around a next-generation subsonic transport concept, the D8 aircraft, and demonstrate the benefit of BLI for this configuration. Results from an unpowered version of the aircraft are validated against a wind tunnel experiment, followed by a comparison of the performance of two D8 configurations: one with conventional, non-BLI propulsors, and one with BLI propulsors. (Full paper requires login).
Computational Assessment of the Boundary Layer Ingesting Nacelle Design of the D8 Aircraft,52nd Aerospace Sciences Meeting, AIAA 2014-0558, National Harbor, MD, January 13-17, 2014.

A survey of gradient reconstruction methods for cell-centered data on unstructured meshes is conducted within the scope of accuracy assessment. Formal order of accuracy, as well as error magnitudes for each of the studied methods, are evaluated on a complex mesh of various cell types through consecutive local scaling of an analytical test function. (Full paper requires login).
Gradient Calculation Methods on Arbitrary Polyhedral Unstructured Meshes for Cell-Centered CFD Solvers,52nd Aerospace Sciences Meeting, AIAA 2014-0558, National Harbor, MD, January 13-17, 2014.

Near-field sonic boom pressure signatures were measured and computational predictions made for a Lockheed-Martin Aeronautics Company low-boom supersonic transport concept, an axisymmetric calibration model, and a 69-degree swept delta wing-body configuration. The pressure signatures were measured in the NASA Ames 9- by 7-foot Supersonic Wind Tunnel at Mach 1.6 and 1.7 in 2011 and 2012. (Full paper requires login).
Computational and Experimental Sonic Boom Assessment of Models for the First AIAA Sonic Boom Prediction Workshop,52nd Aerospace Sciences Meeting, AIAA 2014-0558, National Harbor, MD, January 13-17, 2014.

An embedded-boundary, Cartesian-mesh flow solver is coupled with a three degree-of-freedom structural model to perform static, aeroelastic analysis of complex aircraft geometries. The approach solves a nonlinear, aerostructural system of equations using a loosely-coupled strategy. (Full paper requires login).
Static Aeroelastic Analysis with an Inviscid Cartesian Method,52nd Aerospace Sciences Meeting, AIAA 2014-0558, National Harbor, MD, January 13-17, 2014.

Simulation results for the first AIAA Sonic Boom Prediction Workshop are presented using an inviscid, embedded-boundary Cartesian mesh method. The method employs adjoint-based error estimation an adaptive meshing to automatically determine resolution requirements for each simulation. Results are presented for both mandatory and optional test cases. (Full paper requires login).
Cart3D Simulations for the First AIAA Sonic Boom Prediction Workshop52nd Aerospace Sciences Meeting, AIAA 2014-0558, National Harbor, MD, January 13-17, 2014.

Although Ethernet has long been the standard for connectivity in Local Area Networks (LANs), Remote Direct Memory Access (RDMA) technologies such as InfiniBand provide other benefits that can be useful in a high-end computing environment. Now, converged network protocols such as RDMA over Converged Ethernet may promise the best of both.
A Comparison of 40G RDMA and Traditional Ethernet TechnologiesNAS Technical Report NAS-2014-01, January 2014, NASA Ames Research Center, Moffett Field, CA.

In 2013, 279 users participated in a user survey that addressed 14 NAS service areas. This report provides a summary of the survey results and related activities to improve performance in several key areas: job management/queueing, file systems and storage, data transfer to/from the NAS facility, and software licenses.
2013 NAS User Survey ResultsRead More

A modular procedure is presented to simulate moving control surfaces within an overset grid environment using the Navier-Stokes equations. Gaps are modeled by locally shearing the wing grids instead of using separate grids to model gaps. Grid movements for control surfaces are defined through a separate module, which is driven by an external grid generation tool. Results are demonstrated for a wing with a part-span control surface. Grids for the test case are determined from grid sensitivity studies. Steady and unsteady pressures are validated with wind tunnel data.
A Modular Approach to Model Oscillating Control Surface using Navier-Stokes Equations,5th Decennial AHS Aeromechanics' Specialists Conference, San Francisco, January 22-24, 2014.

Unsteady turbulent flow simulations were performed to investigate the effect of turbulence models on the prediction of rotorcraft hover efficiency (figure of merit). One and two-equation eddy viscosity models were studied, including the use of zonal approximations and detached eddy simulation. Skin friction coefficients were compared with available experimental data. The effects of grid resolution, distance to the far-field boundary, and solution convergence were investigated. Coarse grids, close proximity of far-field boundaries, and inadequate convergence were found to artificially increase the predicted figure of merit from its asymptotic value.
Simulations of XV-15 Rotor Flows in Hover Using OVERFLOW,5th Decennial AHS Aeromechanics' Specialists Conference, San Francisco, January 22-24, 2014.

The NASA Advanced Supercomputing (NAS) Division continuously works to understand and anticipate the changing needs of its user community and to expand support in computational sciences for key NASA goals and initiatives. Here, we focus on challenges related to the rapidly growing area of “big data” analytics and related computational sciences capabilities. This report presents the background, questions, processes, and key findings from an examination of the impact of such issues, and identifies NAS’s next steps, both now and in the future.
Supporting "Big Data" Analysis and Analytics at the NASA Advanced Supercomputing (NAS) Facility,NAS Technical Report NAS-2014-02, January 2014, NASA Ames Research Center, Moffett Field, CA.

This paper provides details on the optimization of phase and amplitude of perturbations for simulated free shear layer flows. The goal of the optimization is to maximize or minimize the rate of growth of the shear layer, based upon first-principles physics-based simulations that represent solutions to the fully nonlinear Navier-Stokes equations. These simulations have been obtained using a unique method that considerably reduces the computational burden normally associated with obtaining such solutions.
Optimization of Perturbation Parameters for Simulated Free Shear Layer Flow,7th AIAA Flow Control Conference, AIAA Aviation Forum, Atlanta, GA, June 2014.

The most amplified (fundamental) wave and its subharmonics trigger the instabilities of a mixing layer and its subsequent development. In the present work, an approach for controlling mixing layers is extended to assess the role of amplitude, phase and number of subharmonics of the most amplified wave. In the earlier study, a Proportional-Integral-Derivative (PID) control technique applied to a spectral solution was shown to be capable of rapidly driving the time-developing mixing layer to a target layer thickness, using the phase shift between the fundamental and its subharmonics as the control parameter.
First Principles Based PID Control of Mixing Layer: Role of Inflow Perturbation Spectrum,7th AIAA Flow Control Conference, AIAA Aviation Forum, Atlanta, GA, June 2014.

This paper reports the results of a computational study that was conducted to explore the effect of various Variable Camber Continuous Trailing Edge Flap (VCCTEF) configurations on the lift and drag of a NASA Generic Transport Model (GTM) wing section at a span-wise location called the break station that marks a sharp change in the wing trailing edge slope. The OVERFLOW solver with the the one-equation Spalart-Allmaras (SA) turbulence model and the two-equation (k — w) Shear Stress Transport (SST) turbulence model was first applied to a NACA0021 airfoil case and the results were compared with experimental data of Harris and ARC2D results.
Drag Optimization Study of Variable Camber Continuous Trailing Edge Flap (VCCTEF) Using OVERFLOW,32nd AIAA Applied Aerodynamics Conference, AIAA Aviation Forum, Atlanta, GA, June 2014.

This paper describes an approach to performing turbulence model verification for the computational fluid dynamics code OVERFLOW on four NASA Langley Research Center Turbulence Modeling Resource (TMR) test cases: 2D zero pressure gradient at plate, 2D planar shear, 2D bump-in-channel, and 3D bump-in-channel. In each case, the results from OVERFLOW compare well with the results from the CFL3D and FUN3D codes.
OVERFLOW Turbulence Model Resource Verification Results,NAS Technical Report NAS-2014-03, June 2014, NASA Ames Research Center, Moffett Field, CA.

This paper demonstrates the power of adaptive mesh refinement with adjoint-based error estimates in verification of simulations governed by the steady Euler equations. The low equations are discretized using a finite volume scheme on a Cartesian mesh with cut cells at the wall boundaries. The discretization error in selected simulation outputs is estimated using the method of adjoint-weighted residuals. Practical aspects of the implementation are emphasized, particularly in the formulation of the refinement criterion and the mesh adaptation strategy.
Toward Automatic Verifcation of Goal-Oriented Flow Simulations,NAS Technical Report NAS-2014-04, August 2014, NASA Ames Research Center, Moffett Field, CA.

Stage separation is a critical technical issue for developing two-stage-to-orbit (TSTO) launch systems with widebody carrier aircraft that use air-breathing propulsion and launch vehicle stages that use rocket propulsion. During conceptual design phases, this issue can be addressed with a combination of engineering methods, computational fluid dynamics simulations, and trajectory analysis of the mated system and the launch vehicle after staging. The outcome of such analyses helps to establish the credibility of the proposed TSTO system and formulate a ground-based test programme for the preliminary design phase.
Conceptual Stage Separation from Widebody Subsonic Carrier Aircraft for Space Access,The Aeronautical Journal, Volume 118, No. 1209, November 2014.