Duensing, Jared C.

Frink, Neal T.

Housman, Jeffrey A.

Hunter, Craig A.

Jensen, James C.

Kiris, Cetin C.

Maldonado, Daniel

McMillin, S. Naomi

Viken, Sally A.

English

NASA Technical Reports Server

Computational Simulations of a Mach 0.745 
Transonic Truss-Braced Wing Design
AIAA-2020-1649
Daniel Maldonado, Jeffrey A. Housman, Jared C. Duensing, James C. Jensen, Cetin C. Kiris
NASA Ames Research Center
Sally A. Viken, Craig A. Hunter, Neal T. Frink, S. Naomi McMillin,
NASA Langley Research Center
AIAA SciTech, January 6th-10th, 2020
Orlando, Florida
Session: MST-12, Modeling and Simulation for Certification and Testing
Scheduled: January 9, 2020 10:30 AM to 11:00 AM
Session Room Name: Bayhill 30
https://ntrs.nasa.gov/search.jsp?R=20200000524 2020-03-11T12:38:03+00:00Z
Outline
• Introduction / Objectives 
• Computational Methods
– Codes
– Modeling Procedure
• Verification Process
– Grid Refinement Study
– Verification on Flight Geometry
• Validation with Wind Tunnel Data
– Free Air
– Wind Tunnel 
– Geometry Sensitivity Study
• Summary
1
Introduction
Boeing Transonic Truss-Braced Wing (TTBW) 
Mach 0.745 Variant 
2
Features:
• High aspect ratio
• High span 
• High L/D 
• Strut braced wing
StrutJury Strut
Objectives
• Establish best practices for NASA CFD codes for  
Transonic Truss-Braced Wing-like configurations.
– Utilize two grid paradigms 
• unstructured mixed-element 
• curvilinear structured overset
• Perform validation study of CFD results compared to 
TTBW wind tunnel experiments. 
3
Description of NASA CFD Codes
Launch Ascent and Vehicle 
Aerodynamics (LAVA)
• Vertex-based RANS 
• 2nd order finite difference 
formulation
• Structured curvilinear overlapping 
grids
• Spalart-Allmaras turbulence model
– Rotation / Curvature Correction 
(RC)
– Quadratic Constitutive Relationship 
(QCR2000)
USM3D from TetrUSS (Tetrahedral 
Unstructured Software System)
• Cell-centered RANS
• 2nd order finite volume formulation
• Mixed-element unstructured 
meshes
• Spalart-Allmaras turbulence model
– With and without QCR2000
4
Structured Overset Grid Generation
1. Geometry clean up and 
preparation using ANSA
2. Surface mesh generation 
using Pointwise
4. Domain Connectivity 
using DCF Module 
of OVERFLOW 
3. Volume mesh generation 
using Chimera Grid Tools 
(CGT) 
5. Minimized overlap 
regions between grid 
using LAVA MIHC
Other Guidelines
• Maintaining a 𝑦" ≤ 1
• Double fringe
• Consistent first layer 
spacing across all 
viscous walls
• Half model with 
symmetry plane
5
Unstructured Mixed-Element Grid Generation
1. IGES CAD imported into Heldenmesh
2. Generate triangulated surface mesh 
7. Half Model with Symmetry Plane
3. Adjust first layer height to 𝑦" ≈ 1.  First 
cell centroid of approximately 𝑦" = 0.5.
4. Cell to cell growth rate of 11-14%
5. Mixed-element mesh with 32 layers of 
prismatic cells for the boundary layer
6. Pyramidal cell transition to tetrahedral 
meshes in the outer grid
6
Verification and Code to Code Comparison
LAVA
• Grid convergence study
• Angle of attack effect on grid 
convergence 
• Flux discretization effect on grid 
convergence
• Wake grid 
• Angle of Attack sweep with best 
practices
USM3D
• Grid convergence study
• Angle of attack effect on grid 
convergence 
• SA vs SA-QCR2000
• Angle of Attack sweep with best 
practices
• Code to code comparison was 
done to remove sensitivity to grid 
type from the simulation, quantify 
the uncertainty, and help diagnose 
cause of discrepancies with 
experimental results
USM3D Sample Simulation
7
Structured Overset Grid Refinement Process
• A scale factor (SF) is used for each 
refinement level 
– 3 Refinement Levels created. 
– Coarse (SF=1), Medium (SF=1.4), Fine 
(SF=2.0)
• Surface grids are refined in Pointwise 
using script
– Edge spacing scaled by inverse of SF
– Number of points scaled by SF
• Scripts used to generate volume grids with 
CGT have SF built-in to account for any 
refinement level
Coarse 14.5M
Medium 35.4M
Fine 105.1M
Resulting Volume Grids
8
Unstructured Mixed-Element Grid Refinement Process
• Three refinement levels are created. 
– Coarse, Medium, Fine
• Mesh refinement and coarsening using Heldenmesh
• Grid sourcing scaled by approximately 1/√2 and √2 to obtain finer and coarser 
meshes
• Scaling of 1/√2 and √2 applied to surface mesh, viscous layers, and volume 
mesh.
Coarse 18.5M Medium 31.3M Fine 59.4M
9
Grid Convergence Comparison - LAVA and USM3D
• For evaluating convergence, the loads 
of the 3 different grid levels are 
plotted against 𝑁 ⁄-. /.
• Linear fit used to evaluate asymptotic 
convergence and estimate the load 
value for infinitely refined grid
N(-2/3)
0 5E-06 1E-05 1.5E-05 2E-050.2
0.4
0.6
0.8
1
1.2
a = 0° , USM3D
a = 1° , USM3D
a = 2° , USM3D
a = 3° , USM3D
a = 4° , USM3D
a = 0° , LAVA
a = 1° , LAVA
a = 2° , LAVA
a = 3° , LAVA
a = 4° , LAVACL
N(-2/3)
0 5E-06 1E-05 1.5E-05 2E-050.02
0.03
0.04
0.05
0.06
0.07
a = 0° , USM3D
a = 1° , USM3D
a = 2° , USM3D
a = 3° , USM3D
a = 4° , USM3D
a = 0° , LAVA
a = 1° , LAVA
a = 2° , LAVA
a = 3° , LAVA
a = 4° , LAVACD
0 5E-06 1E-05 1.5E-05 2E-050.3
0.5
0.7
0.9
1.1
N(-2/3)
0 5E-06 1E-05 1.5E-05 2E-050.2
0.4
0.6
0.8
1
1.2
a = 0° , USM3D
a = 1° , USM3D
a = 2° , USM3D
a = 3° , USM3D
a = 4° , USM3D
a = 0° , LAVA
a = 1° , LAVA
a = 2° , LAVA
a = 3° , LAVA
a = 4° , LAVACD
• LAVA SA-RC-QCR compared with 
USM3D SA-QCR 
• Conditions:
– Altitude at 40,000 feet
– Temperature = 389.97 ∘R
– Mach 0.745– 𝑹𝒆𝒄 = 𝟏𝟑. 𝟏 × 𝟏𝟎𝟔
10
Comparison of loads at 𝝰 = 2∘
Refinement 
Level
Nodes
(Million)
CL CD Cm
Coarse 14.5 0.7543 0.03798 -0.1097
Medium 36.4 0.7640 0.03599 -0.1184
Fine 105.1 0.7677 0.03490 -0.1246
Asymptote ∞ 0.7732 0.03375 -0.1297
Refinement 
Level
Cells
(Million)
CL CD Cm
Coarse 18.5 0.7621 0.03480 -0.1278
Medium 31.3 0.7643 0.03439 -0.1285
Fine 59.4 0.7665 0.03421 -0.1298
Asymptote ∞ 0.7702 0.03367 -0.1313
USM3D  SA-QCR2000
LAVA  SA-RC-QCR2000
CL CD Cm
0.39% 0.8 Counts 1.23%
Difference between codes
Grid Convergence Comparison - LAVA and USM3D
11
Code to Code Comparison – AOA Sweep
a
-0.5 0 0.5 1 1.5 2 2.5
0.025
0.03
0.035
0.04
LAVA
USM3D
CD
a
-0.5 0 0.5 1 1.5 2 2.5
0.25
0.4
0.55
0.7
0.85
LAVA
USM3D
CL
a
-0.5 0 0.5 1 1.5 2 2.5
-0.15
-0.12
-0.09
-0.06
-0.03
0
0.03
LAVA
USM3D
Cm
• LAVA SA-RC-QCR compared with USM3D SA-QCR 
• The code to code comparison at flight conditions was successful in verifying 
the codes would arrive at a similar solution
• Throughout the sweep CL varied by 0.38-0.73%, CD by 2.4 to 6.1 counts
– Slight shift in Cm due to drag differences
12
Wind Tunnel Test - Background
• The 11-ft TWT is a closed-circuit fixed-geometry tunnel composed of a settling 
chamber, a ventilated test section enclosed by a plenum, an arc sector to actuate 
the model, and a diffuser. 
NASA Ames Unitary Plan Wind Tunnels
Courtesy of NASA
Schematic of 11ft TWT
Courtesy of NASA
• A 4.5% scale model was built to be tested in the NASA Ames Unitary Plan 11-foot 
Transonic Wind Tunnel (TWT).
(housing the 
Test Section)
13
Experimental Conditions and Data
Mach 0.745 TTBW installed in 11ft TWT
Courtesy of NASA
• Wind Tunnel Data:
– Raw data (Uncorrected)
– Cavity Correction
• Accounts normal and axial 
forces and pitching moment 
inside of cavity where sting 
attaches to fuselage
– All corrections (Corrected)
• Approximates free air 
condition
14
WBSNPV - Config 23
Wing Body Strut Nacelle Pylon Vertical Tail
V - Config 21
Vertical Tai
Wind Tunnel Test SetupComputational Geometry
15
Validation with Experimental Data
LAVA
• Grid convergence studies
• Free-air simulations
– WBSV
– WBSNPV
• Slotted-wall wind tunnel simulations
– 2nd Order Steady Rans
– Mixed Order Steady Rans
– 1st Order Unsteady Rans
• Simplified wind tunnel
– Inviscid Channel 
– Viscous Wall Wind Tunnel
• Porous Wall
– Full Body
– Half Body
• Sensitivity to Geometry Corrections
– Twisted Wing 
– Trailing Edge
USM3D
• Grid convergence studies
• Free-air simulations
– WBSV
– WBSNPV
• SA vs SA-QCR2000
• Wind Tunnel Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
16
Mesh for Wind Tunnel Validation
39 Million Vertices
31 Million Cells
• Grid refinement was run for both codes
• LAVA simulations were 
run with a medium grid 
resolution rather than 
the fine grid to reduce 
computational cost
• USM3D found their 
medium grid to be 
sufficiently fine
17
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
a, deg.
-2 -1 0 1 2 3 4 5
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
USM3D Free Air
CL
18
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
a, deg.
-2 -1 0 1 2 3 4 5
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
USM3D Free Air
Corrected Experiment
CL
19
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
a, deg.
-2 -1 0 1 2 3 4 5
0.025
0.035
0.045
0.055
0.065
LAVA Free Air
USM3D Free Air
CD
20
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
a, deg.
-2 -1 0 1 2 3 4 5
0.025
0.035
0.045
0.055
0.065
LAVA Free Air
USM3D Free Air
Corrected Experiment
CD
21
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
CD
0.025 0.035 0.045 0.055 0.065
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
USM3D Free Air
CL
22
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
CD
0.025 0.035 0.045 0.055 0.065
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
USM3D Free Air
Corrected Experiment
CL
23
Mach contours on cut plane showing the effects of the 
porous boundary conditions near the wall 
Half Body Porous Wall Simulation 
Mach 
Porous wall boundary 
condition applied at 
clustered regions
Porous Wall Boundary Condition
• Porous-wall boundary 
condition models the 
baffled slots from the 
real wind tunnel
• Boundary condition is 
initialized with a 
constant plenum 
pressure
• Boundary condition 
targets a net mass 
flow of zero by 
adjusting plenum 
pressure
• Baffled geometry is 
approximated using a 
porosity factor
24
Validation with Wind Tunnel Data
Porous Wall – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
a, deg.
-2 -1 0 1 2 3 4 5
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
LAVA Porous Wall
Corrected Experiment
Cavity Corrected Experimentx
CL
25
Validation with Wind Tunnel Data
Porous Wall – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
a, deg.
-2 -1 0 1 2 3 4 5
0.025
0.035
0.045
0.055
0.065
LAVA Free Air
LAVA Porous Wall
CD
26
Validation with Wind Tunnel Data
Porous Wall – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
CD
0.025 0.035 0.045 0.055 0.065
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
LAVA Porous Wall
CL
27
Validation with Wind Tunnel Data
Porous Wall – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
CD
0.025 0.035 0.045 0.055 0.065
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Porous Wall
Cavity Corrected Experimentx
CL
28
Validation with Wind Tunnel Data
Free Air – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
CD
0.025 0.035 0.045 0.055 0.065
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
USM3D Free Air
Corrected Experiment
CL
29
Consistency Across Configurations
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x x
a, deg.-2 -1 0 1 2 3 4 5
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
LAVA Porous Wall
USM3D Free Air
Corrected Experiment
Uncorrected Experimentx
CL
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
a, deg.
-2 -1 0 1 2 3 4 5
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
LAVA Free Air
LAVA Porous Wall
USM3D Free Air
Corrected Experiment
Cavity Corrected Experimentx
CL
Conditions:
TFreestream ≈ 493 ∘R
TStagnation ≈ 550 ∘R
Mach 0.745𝑅𝑒= = 3.31 × 10?
-2∘ < 𝝰 ≲ 4∘
WBSNPV – Config 23 WBSV – Config 21
30
Validation with Wind Tunnel Data
Porous Wall – WBSV Config 21
31
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
Approximation of Loaded Deformation
• Initial 1G geometry
• Designed for 1G loads experienced 
during cruise
• Wind tunnel loaded geometry
• Twist data from Model Deformation 
Measurement (MDM) system
1G
Loaded 
CP
Refinement 
Level
CL CD
1G 0.8480 0.03663
Loaded 0.8446 0.03676
Experiment
Uncorrected
0.7522 0.03305
Change 0.5% 1.3 
Counts
LAVA Porous Wall Simulation
Using Fine Grid Resolution 
32
Rounding the Trailing Edge
• Sharp trailing edge design could not be achieved to due manufacturing tolerances
• Resulted in a model with a rounded bottom portion of trailing edge
• Used tolerance to guide 
modification of existing wing 
mesh. 
• Used CGT to modified the grid to 
replicate rounding affect
Spanwise cut Illustrated 
(Not to scale)
33
• Modified our geometry based on Boeing 
study showing a shift in CL when 
simulating an approximation of rounded 
trailing edge
Rounding the Trailing Edge
x/c
D
ec
re
a
s
in
g 
C p
0 0.2 0.4 0.6 0.8 1
LAVA Porous Wall Rounded TE
LAVA Porous Wall Sharp TE
Experiment Probe Data
565
x/c
D
ec
re
a
s
in
g 
C p
0 0.2 0.4 0.6 0.8 1
LAVA Porous Wall Rounded TE
LAVA Porous Wall Sharp TE
Experiment Probe Data
380
34
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
Rounding the Trailing Edge
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
a
-1 0 1 2 3 4
0.2
0.4
0.6
0.8
1
LAVA Free Air - Sharp TE
LAVA Free Air - Rounded TE
Wind Tunnel Experiment - Correctedx
• Reduced 
difference with 
experimental CL
data by 60%
35
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘~0.3º
Summary
Findings
• Code to code comparison essential for determining that the CFD was being solved 
properly, driving investigations into geometry
• Porous wall shows some improvement over free air:
• In capturing the slope of the CL-⍺ sweep
• Matching L/D performance
• Free air provides significant reduction in resource cost and effort.
• 8 hours vs 3 day run time
• No iterative process to determine Mach number
• Rounded trailing edge showed significant reduction of differences between CFD and 
experimental lift
• In order to improve comparison with wind tunnel data accurate “as-tested” geometry 
of the test article is required
Future Work 
• Apply best practices learned from this study to Mach 0.8 of TTBW
36
Acknowledgements
• This project was funded by Advanced Air Transport Technology (AATT) 
project and its sub-project High Aspect-Ratio Wing (HARW).
• Computer resources were provided by NASA Advanced Supercomputing 
(NAS) facility.
• The authors would like to acknowledge Michael G. Piotrowski for his 
contributions to the interpretation and implementation of the porous wall 
boundary condition into the LAVA solver.
• The authors would like to thank and acknowledge the Boeing team, 
especially Christopher Droney, Neal Harrison, Michael Beyar, Eric Dickey, 
and Anthony Sclafani, along with the NASA technical POC for the BAART 
contracts, Gregory Gatlin. This paper was made possible by them providing 
data on their model, their simulations, and the wind tunnel test.
37
Questions?
Questions?
40
Mach Number for Porous Wall Solutions 
• Porous wall was run with stagnation inflow / subsonic outflow which required 
specifying a back pressure at the diffuser exit
• Back pressure was used to drive the Mach number in the test section
• Iterative process of adjust back pressure was used to converge to appropriate 
Mach number
x
x
x
x
x x
x
x x
x
x
x
x
x
x
x
x
x
a
x
All points within 
0.001 from target 
Mach number 
41
Validation with Wind Tunnel Data
Porous Wall – WBSNPV Config 23
• Conditions:
– TFreestream ≈ 493 ∘R
– TStagnation ≈ 550 ∘R
– Mach 0.745– 𝑅𝑒= = 3.31 × 10?
– -2∘ < 𝝰 ≲ 4∘
x
x
x x x
x x
x x
x
x
x
x
x
x
x
x
x
x
a, deg.
-2 -1 0 1 2 3 4 5
0.025
0.035
0.045
0.055
0.065
LAVA Free Air
LAVA Porous Wall
Corrected Experiment
Cavity Corrected Experimentx
CD
42


Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design

Computational Simulations of a Mach 0.745 Transonic Truss-Braced Wing Design

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