SMALL WIND

CONFERENCE

Bloomington, Minnesota

April 11, 2017

Turbulence and Loads

Dr. David Laino and Dean Davis

Windward Engineering L.C.

TURBULENCE

QUANTIFYING TURBULENCE

©2010 Mick Sagrillo and Amy Taivalkoski

15%

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25%

30%

𝑇𝐼 =𝜎

𝑉𝑎𝑣𝑔

QUANTIFYING TURBULENCE

• IEC 61400 Standards:• -12-1: Power Performance

• Outlines test procedure to evaluate power output under field test conditions

• -1: Design Requirements• Defines external conditions a turbine design is required

to withstand

• -13: Loads Measurement• Outlines test procedure to evaluate operational loading

under field test conditions

TURBULENCE AND POWER

PERFORMANCE

NOTE: The implicit assumption of the methodof this standard is that the 10-minute meanpower yield from a wind turbine is fullyexplained by the simultaneous 10-minutemean wind speed measured at hub height,and the air density.

This is not the case…

TURBULENCE IN DESIGN

Normal Turbulence Model (NTM)

N ORMAL TURBULENCE MODEL (NTM)

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Hu

b H

eig

ht

Win

d S

pe

ed

(m

/s)

Time (sec)

10% 15% 20% 25% 30%

Snapshot for Vavg = 10 m/s

LOAD MEASUREMENTS WRT

TURBULENCE

Requirements:• Must include TI variability• No specified TI magnitude thresholds

WHAT DOES IT ALL MEAN?

Power PerformanceIEC 61400-12

Design LoadsIEC 61400-1 or -2

Loads TestingIEC 61400-13

Industry’s take TI matters TI matters TI matters

Standard’s position Don’t do any adjustments

Creates turbulence classes

Measurements should have variability

Standard’s requirement

Report TI during testing

Pick a turbulence class and simulate

No magnitude requirement but required to capture variety

WindwardEngineering

Not enough turbulencevariability on the site to investigate

Curious to look for clues in the data

DAMAGE E QUIVALENT LOADS

DEL Trusty Brand

m = Material fatigue exponent

Ra = Weighting distribution

2e+6 = 20 yrs of load cycles

YAW MOMENT DEL

YAW MOMENT DEL (12 M /S )

O THER LOAD CHANNELS

Yaw Moment

MF Pitch Mom

Blade Flap Mom

Rotor Torque

SUMMARY

• DELs trend higher with higher turbulence

• The influence of turbulence on DEL varies with load channel

• For a given wind speed the DEL tends to have a linear relationship with TI

• We suspect that the DEL - TI relationship will vary with turbine architecture and control

FUTURE WORK

• See if trends are evident in modeling simulations

• Process data from other turbines to see differences

• Investigate extrapolations to higher TI using observed trends

• Investigate if results from investigation can be used to tailor designs for very high turbulence sites