Adaptive Blades

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Adaptive Blades
Engineered Adaptive Structures V
C. Testa, S. Leone, S. Ameduri The Laboratory of
Smart Structures Vibration and Acoustics
Presented by A. Concilio
The Italian Aerospace Research Centre, CIRA
(Capua-CE) - ITALIA
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Objective

• To illustrate a survey about the activities
  carried out at CIRA reagrding the development of
  integrated adaptive (smart) structural devices
  for blade morphing.
• Smart structure-like approach is the preferred
  but not the only one herein addressed. In fact,
  in certain circumstances, the use of standard
  technology, even improved by the inclusion of
  smart systems, may offer some answers.

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Feasibility studies on the blade morphing

• Main goals
• Analysis of the design solutions for improving
  aerodynamics performances in hover flight
  condition
• Torque tube (ATT CTT - axial or coil activation)
• Comparison among the different architectures
• Aeroelastic couplings
• Architectures for realizing the static twist to
  reduce the tip stall

All the design solutions are somehow based on
the use of smart systems integrated into the
blade. Because of the severe environment, typical
of a rotating blade, the capability of such a
kind of smart devices must be evaluated for the
specific application under consideration
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Anisotropic Torque Tube (ATT)

• Material anisotropic fibre glass laminate
• Basic principle taking advantage of anisotropy,
  axial loads produce cross section rotations
• Axial force generated by SMA wires/ribbons

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ATT Design and Results

• Once geometrical parameters (internal radius,
  thickness and length) have been chosen, an
  optimization process has been carried out to
  define the plies orientation
• highest cross-section rotation
• highest torque moment transmission
• Optimization study Genetic Algorithm
• cost function product between the free edge
  rotation and the constrained transmitted couple
  for a given axial load
• structural integrity check

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This configuration assures under an axial load
of 110 N (more or less a single SMA cable
activation force) a free rotation of 0.038 deg.
and transmitted torque couple of 0.78 Nm.
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• The structural integrity analysis has been
  performed by means of Tsai-Wu criterion
• The safety factor has been estimated for the two
  constraint conditions and for the actuation force
  due to 30 SMA wires

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Integrated SystemATT Actuation on the
Undeformed Blade

• The tube is integrated along the blade axis. One
  base is constrained to the structure (a frame)
  while the other one may only axially slide under
  the action of an axial load produced by the SMA
  wire activation
• The consequent torque moment is transmitted by
  the second base to the closest blade frame. By
  integrating many tubes in serial way along the
  blade span, a selective pitch control of the
  blade may be achieved
• The starting rotation angle of the k-th tube is
  equal to the rotation angle of the outer edge of
  the previous tube this means that it is possible
  to shift the starting pitch angle of the inner
  section of each torque tube

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FEM Simulation (MSC/Nastran)

• Beam element located on the elastic axis of the
  torque tube
• Geometrical data
• (reri)/2 15 mm
• thickness 3.3 mm
• layers (0.3mm for each layer)
• Beam cross section and related inertia moments
  assigned according with the consortium

Stiffness data
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Numerical Results

• Single tube data
• Number of SMA ribbons 40
• Acting force x tube 20000N
• Tsai-Wu safety factor 0.8139

Tip angle rotation about 5o
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CTT Actuation on the Undeformed Blade

• The tube is integrated along the blade axis. The
  bases of the tube are constrained to two
  consecutive frames of the blade. The tube active
  part is constituted by a SMA wire helicoidally
  turned around the internal core of the tube, made
  of a fiber glass laminate winding
• The wire activation produces a torque moment
  acting on the internal core of the tube this
  causes a rotation of both tube and surrounding
  blade structure
• The starting rotation angle of the k-th tube is
  equal to the rotation angle of the outer edge of
  the previous tube this means that it is possible
  to shift the starting pitch angle of the inner
  section of each torque tube

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FEM Simulation

• The blade was modelled through a beam assigned
  with the same mechanic properties (bending and
  polar inertia moments)
• Geometrical data of the actuator
• (reri)/2 15 mm
• Thickness (fiber-glass core
• SMA layer) 8.7 mm
• Layers thickness
• fiber glass (0.3mm)
• SMA winding (6mm)

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Numerical Results

• Single tube data
• Rotation w/o constr. 5.72o. (cld-free w/o blade
  box)
• Tube rotation integrated within the blade 0.86o.
  (clamped-free w blade-box)

Tip angle rotation about 8.6o
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Concentrated Masses Effect

• Basic principle
• to exploit dominant aeroelastic coupling
  phenomena (flap-lag coupling and nonlinear
  bending-torsion coupling)
• simple elements, just like concentrated masses
• the desired blade morphing by exploiting the
  environment of the rotating blade
• smart device devoted only to activate the masses
  displacement when required (on/off mechanism)

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Blade Structural Model

• Hingeless rotor blade modelled as
• elastic long, straight, slender beam undergoing
  lag flap and torsion motion
• moderate deflections with small strains
• homogenous and isotropic material
• chord-wise offsets between the elastic axis,
  tension axis, centre of mass and aerodynamic
  centre
• Structural equations from NONLINEAR EQUATION OF
  MOTION FOR ELASTIC BENDING AND TORSION OF TWISTED
  NONUNIFORM ROTOR BLADES by D.H. Hodges and E.H.
  Dowell

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Blade Aerodynamic ModelGreemberg Theory

• strip theory based on a quasi-steady 2D airfoil
  theory
• all time-dependent terms (including the
  noncirculatory effects) have been imposed to be
  zero
• Theodorsens function C(K) is taken equal to one
• 3D effects are included by means of the steady
  induced inflow

Aerodynamic model from LINEAR FLAP-LAG DYNAMICS
OF HINGELESS HELICOPTER ROTOR BLADES IN HOVER, by
D.H. Hodges and R.A. Ormiston
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Simplified Basic Equilibrium Equations
Aerodynamic loads
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FEM Discretization

• Beam element 11 dofs
• Hermite polynomials for flap and lag
  displacements
• Lagrangian interpolation for torsion angle

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Propulsive Trim Procedure
Initial guess
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Code Validation
LiteraturePh.D Thesis A technique for the
prediction of aerodynamics and aeroelasticity of
rotor blades ( Georgia Institute of Technology,
1988)
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Induced Effect by Lag-Pitch Coupling
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• Aim to reduce the effect due to the lag bending
  moment

Mass location close to the blade root 0.49 m
Masses location close to the blade root 0.49 m
0.735 m 0.98 m

• Lag-pitch aeroelastic coupling causes a negative
  effect for the elastic pitch with respect to the
  blade without masses
• Pitch moment due to masses weight is not effective

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Induced Effect by Flap-Pitch Coupling
Tip pitch variation25
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Tip pitch variation35
Flap-pitch aeroelastic coupling allows to reduce
the blade tip elastic rotation in trimmed
configuration
Tip pitch variation35
Different way to obtain a higher bending
moment.
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3 Kg located at the blade tip
non actuated blade
Mass on
The configuration of the device is regulated by a
SMA actuator connected to the simply supported
edge on the right. SMA contractions and
expansions cause mass lowering and elevation,
respectively.

• 4 SMA ribbons 9.4cm lenght are required
• 8Nblade W is the power to be supplied

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Conclusions

• Two different concepts of torque tube have been
  investigated to obtain static twist.
• The best solution for the tip rotation
  anisotropic torque tube with coil actuation
• The best solution for the power anisotropic
  torque tube with axial actuation
• Best solution from manufacturing aspects?

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Conclusions (contd) Further Work

• As well, 2 kinds of engineering strategies have
  been investigated to obtain static twist
• Inertial Masses show the possibility to obtain
  both twist effect and anhedral configuration
• In this case an optimization study is advisable
  to better define the masses location spanwise
• The possibility to reduce the upper masses
  increasing the arm of the centrifugal force has
  been addressed
• Preliminary results show these solutions to be
  promising

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Acknowledgements

• The activity has been carried out under the
  sponsorship of the EU inside the FRIENDCOPTER
  research program.