effects of inflow wind condition and structural oscillation on … · 2013. 2. 25. · background...

10-11/12/2012 Japanese-Danish Joint Workshop

Future Green Technology

Effects of Inflow Wind Condition

and Structural Oscillation

on Blade Loads of HAWT Rotor

Yutaka HASEGAWA

Nagoya Institute of Technology

CONTENTS

4Background & Objectives

4Inflow effects on blade load - research procedure

- results & discussions

4Oscillation effects on blade load - research procedure

- results & discussions

4Summary & Future works

2/26 Background 1/2

4Many turbines installed in mountainous area, in Japan:

- High turbulence intensity over the complex terrain.

- Special attention should be paid to effects of inflow condition

on fatigue load.

Off-shore wind farm

(Middelgrunden, DK)

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

Tu

rbu

len

ce

in

ten

sity T

I [-

]

Average wind speed U [m/s]

90% quantile

Tu

rbu

len

ce

in

ten

sity T

I [-

]

0 5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

Average wind speed U [m/s]

Tu

rbu

len

ce

inte

nsity T

I [-

]

Wind farm in complex terrain area (Tappi, Aomori, JP)

measured at 50 m elevation measured at 40 m elevation

3/26 Background 2/2

4Increasing size of wind turbines:

Effects of inflow condition and

blade oscillation on the blade loads

have to be predicted in design process.

Increase in Rotor Diameter

⇒ Decrease in eigen freq.

of blade oscillation

- close to rotational freq. for large rotors

- possible resonant oscillation of blade

⇒ Increase in non-uniformity of inflow

into rotor plane,

leads to increased effects from inflow condition

?

Ro

tor

Dia

mete

r [m

]

In order to design large wind turbines

Large Wind Turbine

（D = 126m, P = 5MW）

4/26 Objectives

Clarify effects of inflow condition on blade loads by simple numerical analysis

Clarify effects of blade oscillation on blade loads

by fluid-oscillation coupled analysis

qyaw qy

aw

Yaw misalignment Sheared inflow Turbulent inflow Combined inflow

Two-way coupled analysis model

Displacement &

Velocity of

Blade Oscillation

Aerodynamic Load Aerodynamic

Analysis

Oscillation

Analysis

Blade Oscillation （Multi-Body Dynamics）

Flow Field around Rotor

（Panel Method）

4Objective I :

4Objective II :

5/26 Objective I and Procedure I

Clarify effects of inflow condition on blade loads by simple numerical analysis

qyaw qy

aw


4Objective I :

4Procedure I :

Wind simulation:

Wind shear: Power law

Turbulence: Mann model

1

Aerodynamic load calculation:

Acceleration Potential Method

2

6/26

Top

Bottom

Hub

rotor plane

x z

rotor axis

wind

y

von Karman Spectrum

<Simulation of turbulence by Mann Model

・Generates turbulent wind time series at multiple points on rotor plane

・Takes account of spatial correlation between time series

・Power Spectrum： von Karman Spectrum（isotropic turbulence）

Wind Simulation

6

1722

443

53

2

1 kL

kLLkE K

L ：turbulent length scale

K ：Kolmogorov constant

：viscous dissipation rate

1E-4 1E-3 0.01 0.1 11E-3

0.01

0.1

1

10

100

Pow

er

Spe

ctr

al D

ensity o

f

Win

d S

pee

d E

(k)

[m2/s

]

Wave Number k [m-1]

400 500 600 700 8006

7

8

9

10

11

12

13

Win

d S

pe

ed

W [m

/s]

Time t [s]

Top (h=90m)

Hub (h=60m)

Bottom (h=30m)

Example of turbulent inflow by Mann model

7/26

< Acceleration Potential Method

4 Assume inviscid and incompressible flow

4 Laplace equation for pressure perturbation

4 Representation of rotor blades by spanwise and chordwise pressure distributions

4 Ability to handle three dimensional unsteady flow

without using empirical constants unlike BEM

Euler eq. Laplace eq.

linearized

Aerodynamic Load Calculation Model

pt

1vv

v

Rotor blade represented by pressure

rotor blade

wind

air particle collocation

points

Collocation points on blade

02

2

2

2

2

22

z

p

y

p

x

pp

8/26

Tjæreborg Turbine

Rotor performance

Calculation Condition I

<Rotor configuration I :

4 Tjæreborg Turbine (Denmark)

<Validity of calculation method

pitch control

[Hansen et al., 1989]

Power Coefficient:

hubW

R Tip Speed Ratio:

ratio of the rotor tip speed

to the wind speed

223RW

PChub

P

number of blades 3 rotor diameter 61 [m]

rotational speed 22 [rpm] rated power output 2 [MW]

9/26

<Examples of inflow conditions

4Yawed inflow (uniform inflow with yaw misalignment)

4Turbulent inflow

4Yawed turbulent inflow (turbulent inflow with yaw misalignment)

Calculated Results

Yawed inflow

qyaw

Turbulent inflow

qyaw

Yawed turbulent inflow

4Is summation of individual inflow effects on fatigue load equal to combined inflow effects??

4Yawed inflow effects are not considered in the fatigue load analysis in IEC standard.

+ = ?

10/26 Yawed Inflow 1/3

qyaw

Relative flow to blade section at the top of rotor plane

Yawed uniform inflow

Relative flow

Relative flow

Lift

<Relative flow to the rotating blade section changes periodically

In the rotor plane .....

4Upper half : smaller attack angle lower blade load

4Lower half :

larger attack angle higher blade load


Relative flow to blade section at the bottom of rotor plane

qyaw


Relative flow Relative flow

Lift



4Upper half : smaller attack angle lower blade load

4Lower half :

larger attack angle higher blade load


0 90 180 270 360-80

-60

-40

-20

0

20

40

60

80

=8.0

Fla

pw

ise M

om

ent P

ert

urb

ation

Mp [kN

m]

Azimuth Angle [deg]

qyaw

=10deg

qyaw

=20deg

qyaw

=30deg

W

qyaw



4Upper half : smaller attack angle lower load

4Lower half :

larger attack angle higher load

Definition of Flapwise Moment Flapwise moment fluctuation

due to yaw misalignment at =8

Periodic fluctuation

due to yaw misalignment

qyaw


Lower half

13/26

35 36 37 38 39 40600

700

800

900

1000

1100

1200

Fla

pw

ise M

om

ent [N

m]

Nondimensional Time t/Trev

[-]

TI=0.0

TI=0.1

TI=0.2

Flapwise moment fluctuation

for various turbulence at =8

Turbulent Inflow

Turbulence Intensity :

s : standard deviation of

velocity fluctuation

Whub : velocity at hub height

hubWTI s

Turbulent inflow

<Turbulent Inflow without Yaw Misalignment

4Blade load due to turbulence

8Complex fluctuation of blade load

8 Amplitude of fluctuation increases with turbulence intensity TI

14/26 Yawed Turbulent Inflow 1/2

Effect of yawed turbulence

on fatigue load on blade

qyaw ＋

200 201 202 203 204 205-200

-150

-100

-50

0

50

100

150

200

=8.0

Fla

pw

ise

Mo

me

nt

Pe

rtu

rba

tio

n

Mp [kN

m]

Nondimensional Time t/Trev

[-]

qyaw

=30deg, TI=0.1

qyaw

=30deg, TI=0.0

Blade load fluctuation due to yawed inflow with and without turbulence

<Turbulent Inflow with Yaw Misalignment

4Fatigue load on blade

・Yawed uniform inflow condition

→ Linear increase with yaw misalignment angle

・Yawed turbulent inflow condition

→ Non-linear increase with yaw misalignment angle


0 10 20 300

50

100

150

200

250

300

350

=8.0

TI=0.1Equ

iva

lent F

atig

ue

Load

Seq

[kN

m]

Yaw Misalignment Angle qyaw

[deg]

3d isotropic turbulence

steady inflow3d isotropic turbulence uniform inflow

3d isotropic turbulence TI = 0.1

yawed uniform inflow

15/26

0 10 20 300

50

100

150

200

250

300

350

=8.0

TI=0.1Equ

iva

lent F

atig

ue

Load

Seq

[kN

m]

Yaw Misalignment Angle qyaw

[deg]

only longitudinal component

only lateral component

only vertical component


Yawed Turbulent Inflow 2/2

Effect of turbulence component and yaw

misalignment on fatigue load on blade

qyaw ＋

<Turbulent Inflow with Yaw Misalignment

4Compare effects of turbulent components

longitudinal component

lateral component

vertical component



4Normal Inflow (qyaw=0deg)

a longitudinal comp. has

dominant effect on Fatigue Load

a small effect from

lateral and vertical comp.

4Yawed Inflow

a lateral comp. gives larger effects

with yaw misalignment angle

16/26

Clarify the effects of inflow condition on blade loads by simple analysis

Clarify the effects of blade oscillation on blade loads


qyaw qy

aw



Displacement &

Velocity of

Blade Oscillation


Analysis

Oscillation

Analysis



（Panel Method）

4Objective I :

4Objective II :

16/26 Objectives II

17/26

fy

Reference Data : Wind tunnel experiment conducted by

NREL (National Renewable Energy Laboratory)

■ Configuration of NREL Rotor

Blade num. 2 Rotational speed 72 [rpm]

Rotor diameter 10 [m] Wing section NREL S809

NREL Rotor

Uniform inflow without turbulence

Yaw Misalignment 0～30 [deg]

Wind Speed 5～12 [m/s]

■ Calculation Condition


Calculation Condition II 17/26

18/26

Clarify the effects of inflow condition on blade loads by simple analysis

Clarify the effects of blade oscillation on blade loads



Displacement &

Velocity of

Blade Oscillation


Analysis



（Panel Method）

4Objective I :

4Procedure II :

Procedure II

blades, wake vortices

and tower are modeled

by vortex lattices

Oscillation

Analysis

18/26

19/26

Multi body dynamics

Body

Hinge spring

Modeling

Flapwise Oscillation

Rotor Axis

Edgewise Oscillation

<Multi Body Dynamics Model

4 Represent rotor blade by combination of

Rigid Bodies and Hinge Springs

4 Consider forces on bodies

Aerodynamic, Gravity,

Centrifugal, and Coriolis forces

as well as Restoring and

Damping Moments from Hinges

4 Examine Flapwise and Edgewise oscillations

in the present study

<Verification of Oscillation Model

4 Compare Eigen Frequencies of Static Blade

Mode Calculation Experiment

Flapwise 1 st 7.39 Hz 7.31 Hz

2nd 30.2 Hz 30.1 Hz

Edgewise 1 st 9.27 Hz 9.06 Hz

2nd 64.9 Hz -

Validity of

Oscillation model

Blade Oscillation Model 19/26

20/26

<Blade Load Fluctuation in Flapwise direction

4 Aerodynamic Moment

Integrated moment due to aerodynamic force

Exp. results are obtained from pressure distribution on blade.

4 Structural Bending Moment

Product of spring constant & bent angle

of hinge spring at blade root

Exp. results are obtained by strain gauge installed at blade root.

yawed inflow

W=7m/s

fy=30deg

Exp.

Cal.

Cal.+Tower

1 1010

-4

10-2

100

102

104

106

PS

D o

f F

lapw

ise

Flu

id M

om

ent

[N2m

2s]

Frequency f [Hz]

frev

2frev

3frev f1

PS

D o

f A

ero

dyn

am

ic M

om

nt.

Frequency f [Hz]

Aerodynamic Moment

1st eigen freq. f1=7.44Hz

Rotation freq. frev=1.14Hz

1 1010

-4

10-2

100

102

104

106

PS

D o

f F

lap

wis

e S

tru

ctu

rul

Mo

men

t [N

2m

2s]

Frequency f [Hz]

frev 2frev f1

Frequency f [Hz]

Structural Bending Moment

PS

D o

f S

tru

ctu

ral

Be

nd

ing

Mo

me

nt

Coupled Analysis Results 20/26

21/26

<Blade Load Fluctuation in Flapwise direction

yawed inflow

1 1010

-4

10-2

100

102

104

106

PS

D o

f F

lapw

ise

Flu

id M

om

ent

[N2m

2s]

Frequency f [Hz]

frev

2frev

3frev f1

PS

D o

f A

ero

dyn

am

ic M

om

nt.

Frequency f [Hz]

Aerodynamic Moment


Peaks at rotation freq. and its harmonics →due to Rotational Sampling Effects


Additional peak at 1st eigen freq. of blade structure

4From comparison between Exp. and Cal.,

Calculation results are improved by including tower model.

W=7m/s

fy=30deg

Exp.

Cal.

Cal.+Tower

Coupled Analysis Results



1 1010

-4

10-2

100

102

104

106

PS

D o

f F

lap

wis

e S

tru

ctu

rul

Mo

men

t [N

2m

2s]

Frequency f [Hz]

frev 2frev f1

Frequency f [Hz]

Structural Bending Moment

PS

D o

f S

tru

ctu

ral

Be

nd

ing

Mo

me

nt

21/26

22/26

1 1010

-4

10-2

100

102

104

106

PS

D o

f E

dgew

ise

Str

uct

uru

l M

om

ent

[N2m

2s]

Frequency f [Hz]

1 1010

-4

10-2

100

102

104

106

PS

D o

f E

dg

ewis

e F

luid

Mo

men

t [N

2m

2s]

Frequency f [Hz]

yawed inflow

Edgewise dir.

frev 2frev

3frev f1

W=7m/s

fy=30deg

Exp.

Cal.

Cal.+Tower

frev

2frev f1


Amplitude is much smaller than Structural Bending Moment


Gravitational Force Effects are dominant

4Tower Effects on edgewise moment

Scarcely seen in calculated results

<Blade Load Fluctuation in Edgewise direction

Frequency f [Hz]

Frequency f [Hz]

Aerodynamic Moment Structural Bending Moment

Coupled Analysis Results



22/26

23/26

Inflow condition effects such as

a yaw misalignment

a turbulence

on fatigue load of HAWT rotor have been examined

by simple numerical calculation.

g For turbulent inflow condition,

a Longitudinal component of turbulence has dominant effects on fatigue load.

a Effects from lateral and vertical components are negligible for fatigue load evaluation.

g For combined inflow condition of yaw misalignment and turbulence, a Lateral and vertical components effects increase with yaw misalignment angle.

a 3d turbulence is necessary

for fatigue load calculation.

Summary I

qyaw ＋


Turbulent inflow

24/26

A fluid-oscillation coupled analysis model has been constructed

for the estimation of the flapwise and the edgewise blade loads

of HAWT rotor.

■ Validity of the coupled analysis model is improved

by introducing the tower model into the aerodynamic

calculation for flapwise component.

■ Tower effects can scarcely be seen

in the edgewise structural moment,

which is dominated by the gravitational force.

Summary II 24/26


Displacement &

Velocity of

Blade Oscillation


Analysis

Oscillation

Analysis

25/26 Our Future Work I

fy

Aerodynamic Load

Calculation Model

Structural Oscillation Model

Inflow Wind Model

Co

up

led

A

na

lysis

Power-Train Model

Coupled Analysis

<Design of Turbine Control

4 Include power-train model

4 Decrease fatigue load, power fluctuation

4 Suppress structural oscillation

25/26

26/26

fy

Our Future Work II

Aerodynamic Load

Calculation Model

Structural Oscillation Model

Inflow Wind Model

Co

up

led

A

na

lysis

Floating Structure Model

Coupled Analysis

<Application to Off-shore Turbine

4 Include floating structure model

26/26

27/26

Thank you for your kind attention . . .

effects of inflow wind condition and structural oscillation on … · 2013. 2. 25. · background...

Documents