project number : ps 1.3 development of a smart materials based actively conformable rotor airfoil...
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Project Number : PS 1.3
Development of a Smart Materials Based Actively Conformable Rotor Airfoil
PIs: Prof. Farhan Gandhi
Prof. Mary Frecker
Graduate Student:Andrew Nissly
Penn State University2005 NRTC RCOE Program Review
May 3-4, 2005
Technical Barriers:• Smart actuation must have required authority (under airloads) and bandwidth
• weight, volume, and power constraints• Airfoil cross-section traditionally designed NOT to undergo any deformation
• a fundamental change in design philosophy is required for conformable airfoil• reduction in cross-section stiffness is required
• Large local surface strains in the skin due to shape change require novel materials•Highly-specialized sandwiched composite skins
• Develop analysis and design method for conformable rotor airfoil– achieve significant deformation required to reduce rotor vibration at N/rev– can be viewed as the successor to rotor blade trailing-edge flaps– advantage: integral structure (no hinges, linkages, etc.)
Background/ Problem Statement:
Trailing Edge Flap
Deformable skin
Conformable Airfoil
Approach:• Shape optimization starting with passive structure of predetermined topology actuated by limited number of piezo actuator elements
– max trailing edge vertical deformation (camber) while withstanding airloads– FEA-based optimization method, gradient-based solution method
Expected Research Results or Products:• Develop new design methodology and obtain solution(s) • Demonstrate feasibility of a smart-materials based conformable rotor airfoil
• controllable camber• flexible skin sections to allow large local strains
• Develop a thorough understanding of the physical issues in this design• Build and evaluate demonstration prototype
Task Objectives:• Develop design methodology for a conformable (controllable camber) rotor airfoil using a passive substructure and a limited number of actuators
– Meet specified trailing edge deflection (camber)– Withstand aerodynamic loads– Consider volume (weight) constraint
Concept presented at 2004 review
Numerical Testbed
• Rotor Airfoil (NACA 0012)– Chord length: C = 1.66 ft (50 cm)– Maximum Thickness: 12% chord – Rigid Spar from LE to 25% Chord– Only aft portion is actuated and flexible– High EI, low EA skin
Rigid D-Spar
Axis of Symmetry
Left active member restrained
in vertical position
exaggerated rotation of right active member
Conformable Airfoil Actuation Mechanism
A Cellular TrussMechanism
Active Vertical Members(Actuators)
Passive Linkage
Point Movesup-down asactuatorsextend/shrink
Deformed Configuration-- Top Skin Extends-- Bottom Skin Shrinks
Array of such units along the airfoil chord Accumulation of rotation,Build-up of camber
Limited number of actuators required, Easy to Build
Design Domain Parameterization
+ V (Extension)
-V (Contraction)
Piezoelectric Elements
Skin Elements
Shape Optimization:
• Thickness of passive elements
0 < tlower < ti < tupper
Passive Elements0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
ti
M
iupperi tlA
1max
• Passive Material Area Constrained to % of Amax
Objective function– Maximize Tip Deflection (TD) under
actuation load
– Minimize deflection under air load• Air load unchanged with changes in
airfoil shape
– Two objective functions considered
Optimization Problem
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
SE
TD
J
J(J)Max :function objective (Ratio) criteria Multi
2
1
Kw = fair
J2 = wT K w = Strain Energy (SE)
TD
J1 = Tip Deflection (TD)
Single-criteria objective function: Max (J) = J1 = TD
Sample Optimized Geometry: Comparison of Two Objective Functions
-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
TD Objective Function Ratio Objective Function
0
0.4
0.8
1.2
1.6
2
15 20 25 30 35 40 45
0
2
4
6
8
10
15 20 25 30 35 40 45
Comparison Of Objective Functions – Actuation Deflection
X/Y (%)
Actuation Deflection (mm)
Ratio Objective Function
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
15 20 25 30 35 40 45
3 mm
9 mm
3 mm
9 mm
20% Amax
65% Amax
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
15 20 25 30 35 40 45
3 mm
9 mm
3 mm
9 mm
20% Amax
65% Amax
TD Objective Function
-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
X
Y
X/Y (%)
Airload Deflection (mm)
• Actuation ↑ with ↑ Amax using the TD objective function
• Actuation ↓ with ↑ Amax using the Ratio objective function
• Airload ↓ with ↑ Amax for both objective functions
0
1
2
3
4
5
6
7
2 3 4 5 6
Airload Deflections
TD Objective Function
Ratio Objective Function
Effect of Actuator Thickness
Actuator Thickness (mm)
Deflection (mm)
Actuation Deflections
• Actuation ↑ with ↑ actuator thickness for both objective functions
• Increase in Actuation is smaller for the TD objective function because the passive structure is less rigid and the actuators are already operating close to their free strain
• Airload ↓ slightly with ↑ actuator thickness for both objective functions
Discussion & Conclusions
• Choice of optimal design – Ratio objective function gives solutions with very low
airload deflections.
– TD objective function solutions have a higher airload deflection, however the actuation deflection is considerably higher
• Displacement of 6–8 mm under actuation achieved using four compliant mechanism units– 18-22% change in lift (calculated using X-FOIL)
Best choice is an airfoil optimized using the TD objective function where the deflections due to the airloads are constrained by an upper limit.
Prototype design• Main Structure: 6061-T6
Aluminum (Fatigue Strength: 95 MPa)
• 10 PICA-Thru Piezo Stack Actuators: P-010.20H
Wire EDM Machining
Pro-Engineer Model
Prototype Part
Actuator SelectionPhysik Instrument Tubular Piezo Stack Actuator: P-010.20H
Length: 27 mm, OD: 10 mm, ID: 5 mm
Blocking Force: 1800 N
Max Voltage: 1000 V
Advertised Displacement at 1000 V: 30 μm
Measured Displacement at 1000 V: 25-30 μm
0
5
10
15
20
25
30
0 200 400 600 800 1000
Vendor Data Measured Data
Voltage (V)
Displacement (μm)
ANSYS: Finite Element Analysis
Maximum Stress in Flexures:
35 MPa < 95 MPa Fatigue Strength
Predicted Deflections
- MATLAB Code: 5.6 mm
- ANSYS: 4.0 mm
Active Elements
Skin Design: Camber under Actuation Loads
Skin bubbling
Moment applied at this section
M = 200 N-m/m span
Decrease skin EA more camber
Change in EI less effect(unless baseline EI was very high)
Deformations due toaerodynamic loads < 1
o
EA
EI increased by factor of 10EA reduced by factor of 100
EI
(Low actuation load)
SBB
SBB
Camber under Moderate Actuation LoadsM1 = 400 N-m/m span M2 = 800 N-m/m span
Buckling boundary under actuation loads
Deformations due toaerodynamic loads < 1
o
If skin has low EA, as actuation load increases, need higher EI to avoid buckling
If EA reduced by factor of 50, and EI increased by factor of 600Camber of ~ 3o for M1
Camber of ~ 6o for M2
Camber due to air loads < 1o
EAEA
EI
EI
Process used is analogous to inverse design
What should the properties of the skin be? ….such that-- global (camber) deformations under air load are not excessive-- local deformations due to surface pressure are not significant (no skin ‘bubbling’)-- local sections do not buckle under actuation loads-- actuation forces are not excessive for a desired camber
The process followed gives us EA, EI, and max strain specsWe can then go about designing a composite skin using these specs
Skin Design Conclusions
Low Modulus (silicone) face-sheets
Spacer Flex-Core (Foam?)Composite Skin has low EA, but high EI,and can undergo high max strains
Accomplishments since the last (2004) review
• Shape optimization of series of compliant mechanisms within airfoil:
- Examined effects of passive material constraint, mechanism geometry, and actuator thickness
• Started construction of a bench-top model• Optimized skin properties to avoid buckling and localized
transverse deflections under surface pressure loading while keeping actuation requirements low
Planned Accomplishments for the remainder of 2005
• Complete prototype and conduct bench-top test• Optimization using dynamic analysis
Technology Transfer Activities :• Paper accepted for publication in the 2005 AHS Forum 61 Proceedings• Presented paper at 2004 ASME Design Engineering Technical Conference, Salt Lake City,
Utah• Presented paper at The 15th International Conference on Adaptive Structures and
Technologies, October, 2004, Bar Harbor, Maine
Recommendations at ‘04 review:• The task is a tough problem and shows potential, but needs to look at skin structures as to whether it is practical. It is appreciated to pay attention to last year comments. The task is unique, however potential payoff or practicality is debatable.
Actions Taken :• Completed comprehensive study of optimal skin properties• Completed detailed design of practical design• Demonstration prototype has been constructed and will be evaluated in the lab under quasi-static and dynamic operating conditions
Overall Accomplishments of Task 1.3
• Developed finite element models and optimization algorithms for trailing edge camber control– Topology optimization– Geometry optimization– Concurrent optimization
• Calculated Lift/Drag increment of optimized designs using XFOIL
• Developed a shape optimization method for simpler design
• Studied flexible skin designs
• Developed practical actuation system
• Built prototype and bench-top testing
Forward Path
• Demonstrated that a controllable camber airfoil can be designed and fabricated.
• Controllable camber, as a rotor morphing concept, is ready to move to CRI (formerly RITA) or other 6.2 type activity. The lessons learned and experiences gained can be used in industry-type development and testing activities.
• The lessons learned on how to design structures compliant to actuation loads, stiff to aerodynamic loads, with deformable skins, and requiring modest actuation efforts, should be applied to other rotor morphing concepts.
• Of particular interest to us (and we will propose as an RCOE renewal task) is the use of bistable mechanisms for control of blade twist and blade chord in the outboard regions. Bistable mechanisms provide large stroke with small actuation effort.