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  • 1
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    Parallel Computation of Sensitivity Derivatives with Application to Aerodynamic Optimization of a Wing (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: This paper focuses on the parallel computation of aerodynamic derivatives via automatic differentiation of the Euler/Navier-Stokes solver CFL3D. The comparison with derivatives obtained by finite differences is presented and the scaling of the time required to obtain the derivatives relative to the number of processors employed for the computation is shown. Finally, the derivative computations are coupled with an optimizer and surface/volume grid deformation tools to perform an optimization to reduce the drag of a three-dimensional wing.
    Keywords: Aerodynamics
    Type: HPCCP/CAS Workshop Proceedings 1998; 219-224; NASA/CP-1999-208757
    Format: text
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  • 2
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    Applications of Parallel Processing in Configuration Analyses (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The paper presents the recent progress made towards developing an efficient and user-friendly parallel environment for routine analysis of large CFD problems. The coarse-grain parallel version of the CFL3D Euler/Navier-Stokes analysis code, CFL3Dhp, has been ported onto most available parallel platforms. The CFL3Dhp solution accuracy on these parallel platforms has been verified with the CFL3D sequential analyses. User-friendly pre- and post-processing tools that enable a seamless transfer from sequential to parallel processing have been written. Static load balancing tool for CFL3Dhp analysis has also been implemented for achieving good parallel efficiency. For large problems, load balancing efficiency as high as 95% can be achieved even when large number of processors are used. Linear scalability of the CFL3Dhp code with increasing number of processors has also been shown using a large installed transonic nozzle boattail analysis. To highlight the fast turn-around time of parallel processing, the TCA full configuration in sideslip Navier-Stokes drag polar at supersonic cruise has been obtained in a day. CFL3Dhp is currently being used as a production analysis tool.
    Keywords: Aerodynamics
    Type: 1998 NASA High-Speed Research Program Aerodynamic Performance Workshop; Volume 1; Part 1; 171-203; NASA/CP-1999-209692/VOL1/PT1
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  • 3
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    Hybrid structured/unstructured grid computations for the F/A-18 at high angle of attack (1994)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: At high angles of attack, vortical flows play a crucial role in the maintenance of lift for fighter aircraft. However, under certain conditions, the vortical flow can have an adverse effect on the aircraft. On the F/A-18 the LEX vortex can impinge on the tail; at high angles of attack the unsteady flow from vortex bursting can cause structural fatigue on the vertical tails. At high angles of attack, the flow field can be quite complex, and a computational analysis challenging. A full configuration analysis with viscous structured grids can be computationally expensive and the task of generating the requisite grids can be quite difficult. To mitigate these difficulties and provide a medium-fidelity analysis tool, a hybrid structured/unstructured approach was adopted for this work. In this analysis, the formation and roll-up of the LEX vortex is computed with a structured Navier-Stokes solver, and the resulting vortex propagated downstream with an unstructured Euler solver.
    Keywords: AERODYNAMICS
    Type: NASA. Dryden Flight Research Center, Fourth High Alpha Conference, Volume 1; 17 p
    Format: application/pdf
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  • 4
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    FUN3D Manual: 13.5 (2019)
    In:  CASI
    Details
    Publication Date: 2019-05-24
    Description: This manual describes the installation and execution of FUN3D (Fully-UNstructured three-dimensional CFD (Computational Fluid Dynamics) code) version 13.5, including optional dependent packages. FUN3D is a suite of computational fluid dynamics simulation and design tools that uses mixed-element unstructured grids in a large number of formats, including structured multiblock and overset grid systems. A discretely-exact adjoint solver enables efficient gradient-based design and grid adaptation to reduce estimated discretization error. FUN3D is available with and without a reacting, real-gas capability. This generic gas option is available only for those persons that qualify for its beta release status.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2019-220271 , L-21013 , NF1676L-32825
    Format: application/pdf
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  • 5
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    Emerging CFD Capabilities and Outlook: A NASA Langley Perspective (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-11
    Description: COMSAC goals include increasing the acceptance of CFD as a viable tool for S&C predictions, as well as to focus CFD development and improvement towards the needs of the S&C community. We view this as a symbiotic relationship, with increasing improvement of CFD promoting increasing acceptance by the S&C community, and increasing acceptance spurring further improvements. In this presentation we want to provide an overview for the non CFD expert of current CFD strengths and weaknesses, as well as to highlight a few emerging capabilities that we feel will lead toward increased usefulness in S&C applications.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: COMSAC: Computational Methods for Stability and Control; 48-68; NASA/CP-2004-213028/PT1
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  • 6
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    Navier-Stokes solutions about the F/A-18 wing-LEX-fuselage configuration with multi-block structured grids (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Three-dimensional thin-layer Navier-Stokes computations are presented for the F/A-18 configuration. The modeled configuration includes an accurate surface representation of the fuselage, leading-edge-extension, as well as the wing with and without leading-edge-flap deflection. A multi-block structured volume grid with various topologies is generated using transfinite interpolation technique. The flowfield domain is divided into twenty blocks, each representing a particular geometrical complexity of the configuration. The results are obtained from an algorithm for solving the compressible Navier-Stokes equations that incorporates an upwind-biased, flux-difference-splitting approach. In addition, a newly developed capability that allows for generalized surface patching among blocks is employed. Turbulent results are presented for flow conditions that correspond to recent NASA F/A-18 High Alpha Research Vehicle flight experiments. Good correlations between the computations and the flight test results are disclosed for both surface flow patterns as well as surface pressure distributions.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-3291 , AIAA Applied Aerodynamics Conference; Sept. 23-25, 1991; Baltimore, MD; United States
    Format: text
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  • 7
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    Efficiency and Accuracy of Time-Accurate Turbulent Navier-Stokes Computations (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The accuracy and efficiency of two types of subiterations in both explicit and implicit Navier-Stokes codes are explored for unsteady laminar circular-cylinder flow and unsteady turbulent flow over an 18-percent-thick circular-arc (biconvex) airfoil. Grid and time-step studies are used to assess the numerical accuracy of the methods. Nonsubiterative time-stepping schemes and schemes with physical time subiterations are subject to time-step limitations in practice that are removed by pseudo time sub-iterations. Computations for the circular-arc airfoil indicate that a one-equation turbulence model predicts the unsteady separated flow better than an algebraic turbulence model; also, the hysteresis with Mach number of the self-excited unsteadiness due to shock and boundary-layer separation is well predicted.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 95-1835 , 13th AIAA Applied Aerodynamics Conference; Jun 19, 1995 - Jun 22, 1995; San Diego, CA; United States
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  • 8
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    Predicting the Rotor-Stator Interaction Acoustics of a Ducted Fan Engine (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A Navier-Stokes computation is performed for a ducted-fan configuration with the goal of predicting rotor-stator noise generation without having to resort to heuristic modeling. The calculated pressure field in the inlet region is decomposed into classical infinite-duct modes, which are then used in either a hybrid finite-element/Kirchhoff surface method or boundary integral equation method to calculate the far field noise. Comparisons with experimental data are presented, including rotor wake surveys and far field sound pressure levels for two blade passage frequency (BPF) tones.
    Keywords: Aircraft Propulsion and Power
    Type: AIAA Paper 2001-0664 , Aerospace Sciences; Jan 08, 2001 - Jan 11, 2001; Reno, NV; United States
    Format: application/pdf
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  • 9
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    Modularization and Validation of FUN3D as a CREATE-AV Helios Near-Body Solver (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Under a recent collaborative effort between the US Army Aeroflightdynamics Directorate (AFDD) and NASA Langley, NASA's general unstructured CFD solver, FUN3D, was modularized as a CREATE-AV Helios near-body unstructured grid solver. The strategies adopted in Helios/FUN3D integration effort are described. A validation study of the new capability is performed for rotorcraft cases spanning hover prediction, airloads prediction, coupling with computational structural dynamics, counter-rotating dual-rotor configurations, and free-flight trim. The integration of FUN3D, along with the previously integrated NASA OVERFLOW solver, lays the ground for future interaction opportunities where capabilities of one component could be leveraged with those of others in a relatively seamless fashion within CREATE-AV Helios.
    Keywords: Aircraft Design, Testing and Performance; Computer Programming and Software
    Type: NF1676L-22526 , 2016 AIAA Science and Technology Forum and Exposition; Jan 04, 2016 - Jan 08, 2016; San Diego, CA; United States
    Format: application/pdf
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  • 10
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    FUN3D Airload Predictions for the Full-Scale UH-60A Airloads Rotor in a Wind Tunnel (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An unsteady Reynolds-Averaged Navier-Stokes solver for unstructured grids, FUN3D, is used to compute the rotor performance and airloads of the UH-60A Airloads Rotor in the National Full-Scale Aerodynamic Complex (NFAC) 40- by 80-foot Wind Tunnel. The flow solver is loosely coupled to a rotorcraft comprehensive code, CAMRAD-II, to account for trim and aeroelastic deflections. Computations are made for the 1-g level flight speed-sweep test conditions with the airloads rotor installed on the NFAC Large Rotor Test Apparatus (LRTA) and in the 40- by 80-ft wind tunnel to determine the influence of the test stand and wind-tunnel walls on the rotor performance and airloads. Detailed comparisons are made between the results of the CFD/CSD simulations and the wind tunnel measurements. The computed trends in solidity-weighted propulsive force and power coefficient match the experimental trends over the range of advance ratios and are comparable to previously published results. Rotor performance and sectional airloads show little sensitivity to the modeling of the wind-tunnel walls, which indicates that the rotor shaft-angle correction adequately compensates for the wall influence up to an advance ratio of 0.37. Sensitivity of the rotor performance and sectional airloads to the modeling of the rotor with the LRTA body/hub increases with advance ratio. The inclusion of the LRTA in the simulation slightly improves the comparison of rotor propulsive force between the computation and wind tunnel data but does not resolve the difference in the rotor power predictions at mu = 0.37. Despite a more precise knowledge of the rotor trim loads and flight condition, the level of comparison between the computed and measured sectional airloads/pressures at an advance ratio of 0.37 is comparable to the results previously published for the high-speed flight test condition.
    Keywords: Aerodynamics
    Type: NF1676L-15521 , 69th Annual American Helicopter Society Forum and Technology Display; May 21, 2013 - May 23, 2013; Phoenix, AZ; United States
    Format: application/pdf
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