Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia

Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of

Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Overview of Sandia Wind Turbine Blade

Analysis May 31, 2012

Sandia Blade Workshop

Brian Resor Blade Design Tools and System Analysis Lead

Wind Energy Technologies Department Sandia National Laboratories

brresor@sandia.gov

Problem and Strategy

Simulation and analysis demands associated with aggressive Sandia wind energy technology projects constantly push the limits of the state of the art in wind turbine blade structural and full system aeroelastic simulation

Strategy:

• Utilize a hybrid of existing design codes and in-house developments to meet Sandia needs

• Complement the NREL NWTC Design Codes and commercially available codes

• Create new capabilities only when capabilities do not exist

Beam Properties

Blade Design with NuMAD

3

ANSYS 11.0SP1

JUN 3 2009

16:04:19

DISPLACEMENT

STEP=1

SUB =3

FREQ=9.056

PowerGraphics

EFACET=1

AVRES=Mat

DMX =.328723

1

X

Y

Z

*DSCA=6

XV =-1

DIST=4.376

XF =.266038

YF =-.250333

ZF =3.978

Z-BUFFER

pseudoSERI8

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BlFract

FlpStff (kN/m^2)

EdgStff (kN/m^2)

Modal

ANSYS FE Model

Materials & Layups

Stack Placement

Blade Geometry

NuMAD NuMAD:

Numerical Manufacturing

And Design Tool

ANSYS Analysis

Buckling

Stress &

Strain

Aeroelasticity: The Structural Design & Analysis Cycle

Beam Model:

Up to 6 DOF per node

Wind turbine blades include

• Variable section shapes with twist,

• Multiple materials and composite layups (glass, carbon, balsa, foam, epoxy, adhesives)

• One or more shear webs

Aerodynamic and

structural dynamic

loads applied to the

model

Full system aeroelastic simulation

FAST or ADAMS & AeroDyn

NuMAD History (Nu)merical (M)anufacturing (A)nd (D)esign tool for wind turbine blades

Released initially ~2001 at Sandia; written in Tcl

Experienced a few hurdles along the way:

• Concerns regarding offset node shell element formulations Created motivation for development of tools such as PreVABS/VABS as well as 2D sectional analysis

approaches; some pursued blade models made of brick elements

• Concerns regarding amount of time required to build and solve models

• Concerns about an increasing number of bugs in NuMAD, likely associated with more recent operating systems

A NuMAD tutorial was held at this workshop 2 years ago where it was decided to pursue a major update of the NuMAD tool for the benefit of Sandia users, as well as users in the research community at large

The beginnings of a Matlab-based NuMAD was born in late 2010

Public release of new version planned for end of summer 2012

A 9m Sandia CX-100 example:

NuMAD Interface

Thanks to Jonathon Berg of Sandia for his dedication and

meticulous work toward a complete overhaul and upgrade

of NuMAD!

Sandia Blade Models

CX-100 9m

TX-100 9m

BSDS 9m

Generic WindPACT 33.25m Concept

62.5m Concept

100m Concept

SNL 100m blade

Offshore SHM studies

Active aero load control

Blade reliability collaborative

Radar blade investigations

Sensor blade 1 & 2

Hydro blade acoustics

Scaled underwater turbine

Sandia Supported Projects

New Features of NuMAD 2012

Matlab-based user interface

• Fast

• Bug free

• Easy to customize and develop

Sweep and/or prebend

Excel input

Output for CFD geometry

NREL FAST Blade file output

• 2D method: NREL PreComp

• 3D method: Beam Property Extraction (BPE)

Classical flutter analysis

Blade Sweep/Prebend

Arbitrary blade reference axis can be defined

Excel Input

An advanced user feature

Enables easy parametric inputs

Automatic computation of intermediate airfoil shapes

Easy definition of numerous ply drops

Easy definition of layup stacks; similar to manufacturing drawings

Easy sharing of blade model information

Output for CFD Geometry NuMAD -> Plot3D data format

CX-100 Blade Surface in Pointwise®

Loads application to the FE Model

Normal, tangential and pitching forces can be mapped from BEM simulation (AeroDyn) to all skin nodes in the blade model

Beam Properties Computation Two-Dimensional Approach Pros

• Readily and freely available

• Computationally efficient

Cons

• Limited to 2D analysis

• Simple examples below:

Chosen Tool: PreComp

• Available from NREL NWTC

Three-Dimensional Approach Pros

• Includes three dimensional effects: Boundary conditions and warping

Cons

• Requires creation of the finite element model

Chosen Tool: Beam Property Extraction (BPE)

• Created by David Malcolm, GEC/DNV

• See Malcolm, 2007 Wind Energy for more info

0

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-0.4

-0.2

0

0.2

Blade Span

Chord

Undisplaced nodes

Displaced nodes (exaggerated)

dxdyxyxEflapEI 2),(_ , (1)

dxdyyyxEedgeEI 2),(_ , (2)

dxdyyxyxGGJ ))(,( 22 and (3)

dxdyyxEEA ),( (4)

Calculate Beam Properties Resor,B. “Uncertainties in Prediction of Wind Turbine Blade Flutter.” AIAA SDM 2011

Resor,B. “An Evaluation of Wind Turbine Blade Cross Section Analysis Techniques.” AIAA SDM 2010

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Of (

m)

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BPE

PreComp

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BPE

PreComp

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Edg

Iner

(kg*

m)

VABS

BPE

PreComp

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10-1

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101

BlFract

Flp

Iner

(kg*

m)

VABS

BPE

PreComp

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6

107

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109

1010

BlFract

EA

Stff

(N/m

)

VABS

BPE

PreComp

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BlFract

Edg

Stff

(N*m

2 )

VABS

BPE

PreComp

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Flp

Stff

(N*m

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BPE

PreComp

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GJS

tff (N

*m2 )

VABS

BPE

PreComp

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BlFract

BM

assD

en (k

g/m

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VABS

BPE (215 kg)

PreComp (177 kg)

Edge EA Offset Edge Inertia Edge CG Offset

Flap Inertia EA Stiff. Edge Stiff.

Mass Dens. Flap Stiff. GJ Stiff.

Comparing three techniques: BPE, 2D Section & VABS

Sandia Classical Flutter Capability

SNL legacy capability (Lobitz, Wind Energy 2007) utilized MSC.Nastran and Fortran to set up and solve the classical flutter problem.

• Requires numerous manual iterations to find the flutter speed

A new Matlab based tool has been developed in 2012 by Brian Owens, Texas A&M

• Starting point: Emulate all assumptions of the legacy Lobitz tool

• Continued development and verification: automated iterations, higher fidelity modeling assumptions

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K&C Magnified Flutter Mode, freq=11.87 hz, RPM=61.8

(m)

(m)

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(m)

K&C Magnified Flutter Mode, freq=11.87 hz, RPM=61.8

(m)

(m)

Flutter Mode Shape

0,,, 0 uKKKuKuCCuMM acstcaCa

Matrix Description

M, C, K Conventional matrices

(with centrifugal stiffening)

Ma(Ω), Ca(ω, Ω), Ka(ω, Ω) Aeroelastic matrices

CC(Ω) Coriolis

Kcs(Ω) Centrifugal softening

Ktc Bend-twist coupling

100m Blade Flutter Parameter Study

Resor and Griffith. “Aeroelastic Instability of Very Large Wind Turbine Blades.” Scientific Poster. EWEA Copenhagen, 2012.

Data shown are from classical flutter

analyses of various wind blade

sizes:

• SNL 9-meter CX-100 experimental

blade [Resor, 2011]

• WindPact 33.25-meter 1.5MW

concept blade [Lobitz, 2007]

• SNL 62.5-meter blade (preliminary

design)

• SNL 100-meter blade concept

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-0.5

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x/L

Flutter Mode Shape at 2.1 Hz

Uz

x

Future Work in Aeroelasticity Areas for future research:

Perform blade beam property validations

• Torsion matters: Passive load alleviation via bend twist coupling or blade geometry

Flexible, nonlinear blades

Large deflection blades

Blade materials response characterization

Accurate determination of blade loads

• Especially extreme loads

Continued aeroelastic instability (flutter) tool development and validation

• Will be required for very large blade concepts

Our Goals

Provide Sandia and its partners with a state of the art blade modeling capability and also

Enable the entire research community to benefit from these developments to do cutting edge research

Remainder of 2012 …

• Package and release NuMAD (source and compiled), supporting tools and example blade models

• Software will be available by end of the summer on the Sandia Wind Energy Technologies website

And beyond …

• Some time available for maintenance and integration of externally generated ideas

• There are extensive plans for internal use at Sandia and among partners, which will drive future developments