Title: Advanced Aeroelastic Modeling of Swept Rotor Blades
1Advanced 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
2Rationale 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)
3Modelling issues structural part
Non-linear beam model
Ze the pre-sweep
a swept blade twists when it flaps
4Modelling 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
5Modelling issues structural part
- aft sweep (4.5 m tip deflection)
1st flapwise
2nd flapwise
a flap-torsion coupling appears in all flapwise
modes
6Modelling 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
7Results
sweep geometry defined in UPWIND
project different tip offsets ranging from 1m-6m
are analyzed
8Results
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
9Results
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
10Results
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
11Results
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
12Results
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
13Results
comparison of BEM against free wake for swept
blade aeroelastic analysis results
GAST
U8 m/s, b2
GENUVP
GAST
GENUVP
U8 m/s, b4
14Results
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
15Conclusions
- 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)
16Acknowledgements
- This work was partly funded by the European
Commission under contract SES6 019945 (UpWind
Integrated Project).
17Thanks for your attention END