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Advanced Aeroelastic Modeling of Swept Rotor Blades

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Title: Advanced Aeroelastic Modeling of Swept Rotor Blades


1
Advanced Aeroelastic Modeling of Swept Rotor
Blades
Vasilis A. Riziotis , Dimitris I. Manolas, Spyros
G. Voutsinas National Technical University of
Athens School of Mechanical Engineering Fluids
Section
2
Rationale of sweep
  • Sweeping of blades aims at reducing loads
  • Sweeping activates flap-torsion coupling which
    can be very beneficial in mitigating loads
  • Flap-torsion coupling is also possible by
    structurally tailoring the blade (Sandia Lab)
  • In aerodynamic terms, as the outer part of the
    blade bends it also twists giving lower angles of
    attack and therefore lower aerodynamic loads
  • Load reduction is always important due to its
    direct impact on the cost of energy (e.g.
    lowering the loads allows the increase of rotor
    diameter for the same given strength)

3
Modelling issues structural part
Non-linear beam model
Ze the pre-sweep
a swept blade twists when it flaps
4
Modelling issues structural part
Bending-torsion coupling on pre-swept blades
  • In case of large bending deflections additional
    non-linear terms will become significant in
    torsion moment equation

Including the effect of blade sweep more terms
will appear related to ze
5
Modelling issues structural part
  • aft sweep (4.5 m tip deflection)

1st flapwise
2nd flapwise
a flap-torsion coupling appears in all flapwise
modes
6
Modelling issues aerodynamic part
inboard vortices are shed ahead of those at tip
inducing an up-wash
aerodynamic analysis of the deformed blade
geometry non linear aeroelastic coupling
GENUVP free wake code
7
Results
sweep geometry defined in UPWIND
project different tip offsets ranging from 1m-6m
are analyzed
8
Results
comparison of BEM against free wake for straight
blade
U8 m/s
tangential force dist. (Nt/m)
normal force dist. (Nt/m)
GAST - BEM
axial induced velocity (m/s)
GENUVP - free wake code
9
Results
comparison of BEM against free wake for swept
blade
U8 m/s, b2
Increase of loading towards the tip Lower loads
in more inboard sections
normal force dist. (Nt/m)
Increasing tip sweep
tangential force dist. (Nt/m)
GAST
GENUVP
10
Results
comparison of BEM against free wake for swept
blade
U8 m/s, b4
Similar behavior but larger effect for higher
curvature BEM computations are expected to over
predict power
Increasing tip sweep
GAST
GENUVP
11
Results
U8m/s Free-wake simulations Angle of attack
distributions for swept blade
  • moderate tip offset (a3) affects little the
    a.o.a except at the tip region
  • increasing a and b the complete blade is
    affected

12
Results
comparison of BEM against free wake for swept
blade aerodynamic analysis results
U8 m/s
Aerodynamic Power variation wrt straight blade
BEM
Free W
power scaled for the same blade length
13
Results
comparison of BEM against free wake for swept
blade aeroelastic analysis results
GAST
U8 m/s, b2
GENUVP
GAST
GENUVP
U8 m/s, b4
14
Results
comparison of BEM against free wake for swept
blade aeroelastic analysis results
U8 m/s
Aerodynamic Power variation wrt straight blade
BEM
Free W
power scaled for the same blade length
15
Conclusions
  • Blade sweep activates flapwise bending/torsion
    coupling
  • Aft sweeping gives rise to nose down torsion
    deformation and potentially reduces flapwise
    loads
  • Reduction in loads is accompanied by a reduction
    in power
  • Comparing BEM based against free-wake aeroelastic
    simulations indicates that BEM models
    underestimate power loss.
  • As expected BEM cannot properly account for the
    near wake induced effects driven by skewed shape
    of the tip of the blade
  • Power loss increases with blade curvature (b
    parameter) and tip offset (a parameter)

16
Acknowledgements
  • This work was partly funded by the European
    Commission under contract SES6 019945 (UpWind
    Integrated Project).

17
Thanks for your attention END
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