virginia tech truss-braced wing studies
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Virginia Tech Truss-Braced Wing Studies. J.A. Schetz and R.K. Kapania and TBW Group at VT Multidisciplinary Analysis and Design Center for Advanced Vehicles, Virginia Polytechnic Institute and State University and Collaborators at Georgia Tech, Univ. Florida & UT Arlington and - PowerPoint PPT PresentationTRANSCRIPT
Multidisciplinary Analysis and Design Center for Advanced Vehicles 1
Virginia Tech Truss-Braced Wing Studies
1
J.A. Schetz and R.K. Kapaniaand TBW Group at VT
Multidisciplinary Analysis and Design Center for Advanced Vehicles, Virginia Polytechnic Institute and State University
and Collaborators at Georgia Tech, Univ. Florida & UT Arlingtonand
Vivek Mukhopadhyay (NASA) and B. Grossman (NIA)
Multidisciplinary Analysis and Design Center for Advanced Vehicles 2
Goal of the Research
• Use Multidisciplinary Design Optimization (MDO) to explore the potential for large improvements in long- and medium-range transonic, transport aircraft performance by employing truss-braced wings (TBW) combined with other synergistic advanced technologies.
• Ground Rules for VT Studies:Mach 0.85 cruiseAll-metal airplanesGE90 type enginesFocus on truss benefits
Multidisciplinary Analysis and Design Center for Advanced Vehicles 3
Original Pfenninger Vision
Large span wing to reduce induced drag
Thin wing at root for laminar flow
Fuselage profileFor low wetted area
Optimized truss support to reduce wing weight-
Reduce interference drag
Wing tip for vortex control
Pfenninger, W., “Laminar Flow Control Laminarization,” AGARD Report 654, “Special Course on Concepts for Drag Reduction” , 1977
Multidisciplinary Analysis and Design Center for Advanced Vehicles 4
Main Mission (“777 ER”)
• Use MDO to design 305-passenger, 7730 nmi range, Mach 0.85 transport aircraft of Cantilever, Strut-Braced-Wing (SBW), and Truss-Braced Wing (TBW) configurations
11,000 FTT/O Field Length
7730 NMI Range
Climb
Mach 0.85 Cruise
140 KnotsApproachSpeed
Mach 0.85
350 NMIReserve Range
11,000 FT LDGField Length
Multidisciplinary Analysis and Design Center for Advanced Vehicles 5
MDO Design Environment
Weight Estimation
TOGW Convergence
Optimizer
Performance,Cost Function,
Constraints
Parametric Geometry
Baseline Design
Propulsion
Aerodynamics
Structural Optimization
Fuel Loading
Design Environment N^2 Diagram ModelCenter Environment
Design Environment Block Diagram
Multidisciplinary Analysis and Design Center for Advanced Vehicles 6
Propulsion Model
• Dimensions and weights– Simplified VT model similar to Mattingly
Elements of Propulsion: Gas Turbines And Rockets• Performance:
1. Simplified model2.NASA fixed deck
• “GE-90-like”3.NPSS or Reduced-order NPSS from GT
0.55
0.555
0.56
0.565
0.57
0.575
0.58
20 25 30 35 40 45 50Altitude[kft]
TSFC
[lbm
/hr/l
b]
Fixed Deck, 100% ThrottleSimplified, Tmax=75 klb
M=0.85
Multidisciplinary Analysis and Design Center for Advanced Vehicles 7
Aerodynamic Model• Calculates:
– Aerodynamic drag– Aerodynamic loading (input for structural design module)
• Drag breakdown models:– Induced drag based on Trefftz plane model– Friction/Profile drag based on semi-empirical methods– Wave drag based on the Korn Equation– Interference drag based on literature and response surfaces from offline CFD
Multidisciplinary Analysis and Design Center for Advanced Vehicles 8
Structural Design Requirements• Total of 17 cases:
• 2.5 g 100% / 50% fuel• -1 g 100% / 50% fuel• 2 g taxi bump• 12 gust cases, 50% 100% fuel, various
altitudes– Motivated by low wing loading MDO
designs– Simplified discrete gust modeling – Using gust alleviation factor
• Designs evaluated for flutter performance post MDO
FlutterEnvelope
Mach
Altit
ude
(x10
3 ft) Vc
Multidisciplinary Analysis and Design Center for Advanced Vehicles 9
Structural Design Methodology
• Estimation of load carrying structural weight– Bending and shear material– Structural optimization
• Finite element analysis– Stress, displacement and buckling
constraints – Flutter constraints with geometric
stiffness influence• Structural response surface
model used in MDO
t1=(t/c) ·c /2
t0
cst
z
xt2
BC
AD
Wing Structural Weight Estimation
Evaluate Response Surface
Design Variables
Wing Weight
Response Surface Model
Offline RSM generationLatin-Hypercube SamplingKriging Surrogate Model
Multidisciplinary Analysis and Design Center for Advanced Vehicles 10
TBW Weight Estimation
• Detailed physics based wing system structural weight estimation– In-house tool optimizes
for bending and shear material weight
• Other components: – FLOPS: secondary weight– Folding wing penalty– Fuselage pressurization
penalty
Multidisciplinary Analysis and Design Center for Advanced Vehicles 11
Performance Constraints• Range ≥ 7730 [NM] + 350 [NM] (reserve)• Initial Cruise ROC ≥ 500 [ft/min]• Max. cl (2-D) ≤ 0.8• Available fuel volume ≥ required fuel volume• 2nd segment climb gradient (TO) ≥ 2.4% (FAR)• Missed approach climb gradient ≥ 2.1% (FAR)• Approach velocity ≤ 132.5 [kn.]• Balanced field length (TO & Land.) ≤ 11,000 [ft]• Cruise altitude ≤ 48,000 [ft]
Multidisciplinary Analysis and Design Center for Advanced Vehicles 12
Truss Topology Optimization Study
• Triangular Loading • Two-dimensional analysis• Buckling not included• Single load case
15% Volume Fraction
Fewer MembersLarger tip deflectionLarger strain energy
• All designs with same volume fraction have same mass
Multidisciplinary Analysis and Design Center for Advanced Vehicles 13
Muldisciplinary Design Optimization Study
• Cost functions: Minimum fuel/emissions and TOGW• Configurations
– Cantilever– Strut-Braced wing (SBW)– Single Jury TBW– 2-Jury TBW– 3-Jury TBW
• Aggressive laminar flow• Aggressive junction fairing • Fuselage riblets
Multidisciplinary Analysis and Design Center for Advanced Vehicles 14
Minimum Fuel/Emissions Design Study
Active Constraints
range, deflection range, fuel
range,clmax range,clmax, Vapproach
range,clmax, Vapproach
Multidisciplinary Analysis and Design Center for Advanced Vehicles 15
Minimum Fuel/Emissions Design StudyB777: 183
-33%B777: 20
+80%
B777: 512-8%
B777: 10
+160%
B777: 71+11%
B777: 106
+70%
Multidisciplinary Analysis and Design Center for Advanced Vehicles 16
Minimum TOGW Design Study
Active Constraints
range, balanced field length, Vapproach
range range, initial cruise rate of climb, Vapproach, clmax
range, initial cruise rate of climb, fuel
range
Multidisciplinary Analysis and Design Center for Advanced Vehicles 17
Minimum TOGW Design StudyB777: 183
-26%
B777: 20
+50%
B777: 512
-10%B777: 10
+80%
B777: 71-17%
B777: 106+40%
Multidisciplinary Analysis and Design Center for Advanced Vehicles 18
Comparison of Designs: Min. Fuel and Min. TOGW
B777: 183
B777: 20
B777: 512
B777: 10
B777: 71B777: 106
Multidisciplinary Analysis and Design Center for Advanced Vehicles 19
1-Jury TBW Configurations
Minimum Fuel/Emissions Minimum TOGW
Multidisciplinary Analysis and Design Center for Advanced Vehicles 20
MDO Configurations: Drag BreakdownMinimum Fuel
Minimum TOGW
- All minimum fuel configurations cruise altitude is between 46,000 to 48,000 ft - Increasing number of members reduces induced drag and increases profile drag- Additional surface area from more members reduces system benefit- Fuselage drag reduction is needed.
Multidisciplinary Analysis and Design Center for Advanced Vehicles 21
SB
W
2-Ju
ryVc
FlutterEnvelope
1-Ju
ry
3-Ju
ry
• Flutter margin reduces with increasing number of members due to higher span
• Passive and active control measures under investigation• Passive methods
– Ballast mass– TBW geometry modification: parametric study
– Aeroservoelasticity
Mach
Altit
ude
(x10
3 ft)
Minimum FuelMinimum TOGW
SB
W
2-Ju
ry
Vc
FlutterEnvelope
1-Ju
ry
3-Ju
ry
Mach
Altit
ude
(x10
3 ft)
Flutter Boundary of TBW Airplane Designs
Flutter Mach numbers for 100% fuel at 2.5g pull-up maneuver
Multidisciplinary Analysis and Design Center for Advanced Vehicles 22
Flutter Ballast Mass Study: Ballast Mass is 2% of Wing Mass
• SBW Flutter speed: VF=588 fps, MF=0.526; 600 lb Ballast mass• Best improvement of 1.1% with mass at 36% span, 98% chord• Very low sensitivity to ballast mass location
Multidisciplinary Analysis and Design Center for Advanced Vehicles 23
Flutter Ballast Mass Study: Ballast Mass from 2% to 8%
• Very low sensitivity to size and location of ballast mass
Multidisciplinary Analysis and Design Center for Advanced Vehicles 24
Truss-Braced Wing Geometry Parametric Study
• Influence of selected geometric parameters on aeroelastic performance of TBW– Strut-sweep (ΛS), Wing-strut span intersection (η)– SBW, TBW 1-jury, TBW 2-jury, TBW 3-jury
• Same cross-sectional dimensions for each configuration– Chord, t/c ratio– Values correspond to TBW 1-jury configuration (from MDO)– Each configuration sized for same requirements
Multidisciplinary Analysis and Design Center for Advanced Vehicles 25
Comparison of TBW Configurations (η=55%, b/2=175 ft, ΛW =10°)
• Addition of jury strut members– Reduces wing weight– Largest reduction (21%) from SBW
to TBW 1-jury• TBW configurations have similar
flutter boundary– Low sensitivity to strut-sweep
• TBW 1-jury and 2-jury offer 19% increment in flutter boundary with 14% higher weight
• TBW 3-jury offers 49% increment in flutter boundary with 20% higher weight
Multidisciplinary Analysis and Design Center for Advanced Vehicles 26
Comparison of TBW Configurations (η=70%, b/2=175 ft, ΛW =10°)
• Addition of jury strut members – Reduces wing weight – Largest reduction (14%) from SBW to
TBW 1-jury
• TBW configurations show strong sensitivity to strut-sweep
– Significant flutter boundary increment from SBW
• TBW 1-jury and 2-jury have similar weight and flutter boundary
– 33% increment in flutter boundary with 20% higher weight
• TBW 3-jury offers 75% increment in flutter boundary with 8% higher weight
Multidisciplinary Analysis and Design Center for Advanced Vehicles 27
SBW Flutter modes (sea-level, b/2=175 ft, ΛW =10°)
Multidisciplinary Analysis and Design Center for Advanced Vehicles 28
TBW 3-jury Flutter modes (sea-level, b/2=175 ft, ΛW =10°)
Multidisciplinary Analysis and Design Center for Advanced Vehicles 29
Conclusions and Future Work• TBW airplane configurations offer significant performance benefits• Higher span increases weight and reduces flutter speed• Outboard wing-strut intersection location
– Increases wing weight in present study due to active buckling– Increases flutter speed for TBW configurations
• Larger difference in wing- & strut-sweep could be used to help flutter performance– Flutter speed sensitivity to strut-sweep increases with spanwise intersection location– Airplane MDO would show multidisciplinary influence
• Large benefit in wing weight reduction and flutter boundary increment from SBW and TBW configurations– TBW 3-jury offers highest benefit in flutter performance
• Ongoing efforts and future work– Active control techniques– Body-freedom flutter and nonlinear aeroelasticity
Multidisciplinary Analysis and Design Center for Advanced Vehicles 30
Backup Slides
Multidisciplinary Analysis and Design Center for Advanced Vehicles 31
Minimum Fuel/Emissions Design StudyB777: 183
-33% B777: 20
+80%
B777: 4340+18%
B777: 512-8%
B777: 10
+160%
B777: 71
+11%
B777: 106
+70%
Multidisciplinary Analysis and Design Center for Advanced Vehicles 32
Minimum TOGW Design StudyB777: 183
-26%
B777: 20
+80%
B777: 4340
+12%
B777: 512
-10%B777: 10
+80%
B777: 71-17%
B777: 106+40%
Multidisciplinary Analysis and Design Center for Advanced Vehicles 33
Comparison of Designs: Min. Fuel and Min. TOGW
B777: 183
B777: 20
B777: 4340
B777: 512
B777: 10
B777: 71
B777: 106
Multidisciplinary Analysis and Design Center for Advanced Vehicles 34
Minimum Fuel/Emissions Design: 1-Jury TBW Buckling and Flutter Mode Shapes
Buckling Mode: 2.5g pull up Buckling factor = 1.8
Buckling Mode: 2g taxi-bump Buckling factor = 1.0
Flutter Mode: 2.5g, 100% fuel, Sea-levelVf = 300 fps, 1.7 Hz, reduced freq. = 0.32
• Global wing buckling mode for 2.5g pull-up• Strut buckling mode for 2g taxi-bump • Flutter mode: combination of 3 modes: two
bending + torsion