Document
AIAA SciTech 2016, Jan 4-8 2016, San Diego, CA www.nasa.gov Joseph A. Garcia, John E. Melton, Michael Schuh, Kevin D. James, Kurt R. Long NASA Ames Research Center Dan D. Vicroy, Karen A. Deere, James M. Luckring, Melissa B. Carter, Jeffrey D. Flamm NASA Langley Research Center Paul M. Stremel, Ben E. Nikaido, Robert E. Childs Science and Technology Corporation
NASA ERA Integrated CFD for Wind Tunnel Testing of Hybrid Wing-Body Configuration
Guidelines
• Overview • Efficient Use of Multiple CFD tools • CFD Quality Assessment • CFD Wind Tunnel Support • Lessons Learned and Simulation • Conclusions
Outline
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explored various ERA Project enabling technologies to reduce environmental impact of aviation. Wind tunnel tests performed to evaluate propulsion-airframe interference effects Extensive CFD was used to assist these tests in producing high quality data with minimal hardware interference and extrapolation to flight. High-level summary of how NASA utilized multiple CFD simulations tools in support of the wind tunnel test. CFD simulation guidelines based on post-test aerodynamic data.
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Overview
TetrUSS GridTool
• Overset grids via the Chimera Grid Tools • SA and SST turbulence model • Unstructured tetrahedral meshes via • SA turbulence model • Unstructured prismatic/tetrahedral meshes via AFLR3 • SA turbulence model • Unstructured prismatic/polyhedral meshes • SST turbulence model STAR-CCM+ – OVERFLOW – USM3D – FUN3D – 3 NASA’s CFD Solvers utilized: 1 Commercial CFD Solver utilized:
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Efficient use of Multiple CFD Tools
CFD Solvers and Methods
Sample FUN3D Mesh Sample STAR-CCM+ Mesh Sample Overflow Mesh Sample USM3D Mesh
Efficient use of Multiple CFD Tools
Geometry and Mesh Generation
‘Miniwall’ Application
CFD Quality Assessment
CFD Quality Assessment
CFD was used to provide highest quality experimental testing • Sting selection • Ejector selection • Acoustic array selection • 40’x80’ sting installation
CFD Wind Tunnel Support
CFD Wind Tunnel Support
*Simulations run in free air Long Forward Sting Short Forward Sting = 0.2 ∞ Long Aft Sting Short Aft Sting OVERFLOW: M
CFD Wind Tunnel Support
Sting Selection
° = 20 α α α α = 0.2 ∞ *Simulations run in free air Long Forward Sting Short Forward Sting USM3D: M ° ° ° = 20 = 20 β β β β β β β β = 12 ) α α α α Clean = 0.2 - Cp ∞ Sting_conf Cp= (Cp ∆ ° ° = 0 = 0 OVERFLOW: M β β β β β β β β
CFD Wind Tunnel Support
Sting Selection
Long Ejector ) Short Ejector LongEject ) ° - Cp Clean = 20 α α α α - Cp ShortEject = 0.2 ∞ Ejector_conf Cp= (Cp ∆ *Simulations run in free air Cp= (Cp Overflow: M ∆
CFD Wind Tunnel Support
Ejector selection
40x80 Run 009 Array at 96” below Angle of Attack Array 48 inches below wing, 40x80 Run 180 * Simulations run with walls and supports 40’x80’ Wind tunnel data Pitching Moment Coefficient Array at 48” below = 0.2 ∞
Vertical Placement
Angle of Attack No Array, Landing in 40x80, STAR-CCM+ Array 24 inches below wing, STAR-CCM+ Array 48 inches below wing, STAR-CCM+ Array 96 inches below wing, STAR-CCM+ STAR-CCM+: M Pitching Moment Coefficient Array at 24” below
CFD Wind Tunnel Support
40’x80’ Acoustic array selection
~ 75% 120° Directivity * Simulations run with walls and supports ~ 75% ° ° ° ° = 12 α α α α = 0.2 ∞ 90° Directivity FUN3D: M
Horizontal Placement
~ 75% Cp comparison with and without Array at ~ 75% Span location 60° Directivity
CFD Wind Tunnel Support
40’x80’ Acoustic array selection
Faired collar * Simulations run with walls and supports = 0.2 ∞ Angle of Attack No collar No Collar, STAR-CCM+ Faired Collar, STAR-CCM+ Original Collar, STAR-CCM+ STAR-CCM+: M Pitching Moment Coefficient Original step collar
CFD Wind Tunnel Support
40’x80’ sting installation
&
Lessons Learned
Simulation Guidelines
Lessons Learned & Simulation Guidelines
Time accurate run * Simulations run with walls Modified Post ° ° ° ° = 12 CD% 6.4% 0.35% ∆ α α α α CL % = 0.2 -4.6% ∆ -0.53% ∞ No Post no post Time accurate run modified post FUN3D: M Original Post
Lessons Learned & Simulation Guidelines
Support Post Unsteadiness
Experimental Value ~10% drop in Lift coefficient Time Accurate (DT=20, 25 subiteraions) ° ° ° ° = 20 α α α α Krueger structural bracket = 0.2 ∞ FUN3D: M Non-Time Accurate
Dependency on time integration process
Landing Krueger *similar results obtained with Star-CCM+ using the SST turbulence model and with OVERFLOW using SA model.
Lessons Learned & Simulation Guidelines
High Alpha CFD flow predictions
~10% drop in Lift coefficient ° ° ° ° = 20 α α α α = 0.2 ∞ Experimental Value FUN3D: M
Time accuracy study effect on HWB landing configuration
Lessons Learned & Simulation Guidelines
High Alpha CFD flow predictions
Lift coefficient subiteration DT=10, 100 subiterations Turbulence Flow variables ° ° ° ° = 20 α α α α = 0.2 ∞ FUN3D: M Residual subiteration Convergence Flow variables Turbulence DT=10, 10 subiterations Lift coefficient subiteration
Lessons Learned & Simulation Guidelines
High Alpha CFD flow predictions
processed for later CFD analysis.
– Supported experimentalists in evaluating interference – Provided alternate support options to reduce unwanted effects – NASA’s CFD solvers: OVERFLOW, USM3D, and FUN3D – Commercial CFD solver STAR-CCM+ – Enabled direct knowledge on specific testing setup – Provided key insight to how test data was measured and post- CFD was an integral part of NASA’s ERA project. Efficient use of multiple CFD solvers successfully used to provide timely insight. CFD analyst worked side-by-side with wind tunnel experimentalists throughout entire project. Lessons Learned and CFD simulation guideline development possible due to available test data.
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Conclusions
The NASA ARMD Environmentally Responsible Aviation Project provided multi-year funding for both the wind tunnel testing and CFD analysis. Boeing support staff played an integral part in the success of the tests
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Acknowledgements
) in terms of the FUN3D grid units.
∞ ). In FUN3D, the time step is normalized by the ∞ Time Step Selection Rationale The rationale used to select these CFD time steps was to express them in terms of a physical vortex shedding Strouhal number (St) of 0.25. This was done since the nominal Strouhal number of many unsteady separated wake flows tends to fall into a small range between 0.15 and 0.25. Further, the Strouhal number is defined as: St = fL/U. Where, f is the frequency, L is the relevant length scale, and U is the relevant velocity. In order to express St in terms mof a CFD time step (DT), the Strouhal number equation is rewritten such that the frequency f=1/DT, and the velocity U is set to freestream (U sound speed. This will then yield what is referred to as the time step based Strouhal number (StDT) as follows: StDT = L/(DT*M Next, the ratio of the time step Strouhal number (StDT) to the physical Strouhal number (St) is used as a coarse measure of time integration accuracy. For good time accuracy, this Strouhal ratio, StDT/St must be at least 20, as the second-order backwards-difference time-integration scheme requires roughly that many points per period assuming a simple sinusoidal oscillation for high accuracy. An even higher ratio is needed if any part of the unsteady flow changes more rapidly than the gross features like integrated loads, and this is very common. Thus, the ratio of Strouhal numbers, StDT/St should be 20 or greater, by an unknown amount, to achieve good time accuracy.
CFD Wind Tunnel Support
14’x22’ Wind Tunnel Corrections
Trip Dots Trip Dots Without With Darker areas on model = laminar Lighter patch = transition due to presence of Krueger bracket ∞ ∞ V V Lighter patch = transition due to bug Upper Surface Thermal Imaging Upper Surface Thermal Imaging