the use of windsim for detailed site verification analysis

Use of WindSim for Site verification:

Sector Management, a case study

Beatrice Pistoni

[email protected]

WindSim User Meeting 2014

Tønsberg, 26-27 June 2014

Tønsberg, 26-27 June 2014 User Meeting

Abstract

Short overview of the case study

Analyzing an approach of Sector Management using WindSim

Evaluating the effects of Sector Management both on AEP and Ieff in the case study

Discussing about the benefit of a Sector Management calculation in WindSim

Focusing on Turbulence analysis


Surrounding Area

Hill and forested area: 350 800 m a.s.l

Site Area

700 m a.s.l.


Layout & Technology

13 WTGs positioned on an regular layout on a plateau, stretching from SW to NE

(690 m a.s.l) ; interdistance 1.6D

Technical features

E70 E4 2.3MW

Hub 57m

D 71m

Prevailing sectors: NNW and SSE


Site: orography and vegetation

High complexity site slopes with inclination higher than 35°

mainly covered by forest

Incl.(°)

H = 11÷14m


Wind Data

2 MET STATIONS: related to the same position, since installed one after the other,

with different configurations and heights (22m / 44m)

Mean wind speed

@ 22m= 6.66 m/s

@ 44m= 8.46 m/s

Met mast location very close to the

edge of the plateau in an area not

covered by forest

725 m a.s.l


Vertical wind profile at met station (44 m)

NNW N SSE

Profiles reveal the terrain complexity that needs to be represented by CFD model, in

order to describe the aerodynamic effects involved


Climatologies

2nd :Synthesized Time history @44m

Using correlation coefficient on 20m

1st : Correlation 20/44m

at 44m met mast

Time history .tws @44m

[For IEC Classification]

Weighted Frequency table.wws @44m [for AEP]

.wws .tws

8.12m/s 8.46 m/s


WindSim Model

Large model 20x20km / 80 m horizontal resolution

Nesting model 6x6km / Variable horizontal resolution (uniform 15 m in the 2x2 km area)

Variable vertical resolution (with a constant step of 11.1 m in the first 100 m)

full convergence: 3000 iterations using the SEGREGATED solver


Vertical profiles at met station – Method of the

displacement shift

NNW

N

SSE

Displacement height = 8m

Reduce Turbine Hub and

Met Mast Heights (=h-8m)


Wind Resource

Given the orography and the wind rose of the site, there is a pronounced wind

acceleration at the met station position, with average winds around 8.4 m/s

Wind resource slowly decreases moving towards turbines with Vave=7.42 m/s

57m


Turbulence Analysis

Evaluation of turbulence intensity measured experimentally at met station

Calculation of mean turbulence intensity Iref at the hub (57 m) of every wind turbine

using WindSim aerodynamic solution and the experimental data from the met station

Calculation of Ichar at the hub (57 m) of every wind turbine, using Iref and the

associated standard deviation

(IEC 61400-1 – 2nd ed.)

refIrefchar II

refIrefrep II 28.1

Calculation of Irep and Ieff at the hub (57 m) of every wind turbine, considering

Frandsen model to account for the wakes of the surrounding turbines

(IEC 61400-1 – 3rd ed.)

0.2 vref ÷ 0.4 vref

0.6 vrate ÷ vcut-out C

B

A

S

sm /195Wind Speed Range


Turbulence analysis at Mast

In the turbulence analysis, just the 44m data were used (easier extrapolation of

turbulence intensity at hub heights 57m).

A comparison between the two TI trends, related to the two met stations, at the same

height (20 m), was carried out.

Trends overlap quite well: measurement interval of mast_44m is

representative of long term turbulence.

20m


Turbulence at Mast

Experimental values at Met mast (44m) shows high TImean=16.5% at 15 m/s

According to the IEC 61400-1 2nd ed., the characteristic value of turbulence intensity,

Ichar (84th percentile of TImean) at met mast, was evaluated (Ichar=19.9% at 15 m/s)


Turbulence at Mast

According to the IEC 61400-1 3rd ed., the representative value of turbulence intensity,

Irep (90th percentile of Timean) at met mast, was evaluated (Irep=20.9% at 15 m/s)

High turbulence values Irep mainly due to contributions of prevailing sectors

PREVAILING SECTORS


Turbulence at WTGs (IEC 61400-1, 2° ed.)

At WTGs, Ichar was calculated coupling mast turbulence with CFD analysis.

Results indicates Ichar above the class A limit for every turbine in a wide range of wind

classes.

WTG02


Turbulence at WTGs (IEC 61400-1, 3° ed.)

Ieff effective turbulence takes into account both the structural stress of turbine

components’s material, using the Wholer exponent m, and the wake effects from

neighbouring wind turbines, according to Frandsen study.

WTG02 Ieff above class A

in a wide range of

wind classes


Sector Management: strategy

Managed WTG sector action

Eol-02 NNE-ENE-SSW-WSW off






NNE

ENE

SSW

WSW

Wind rose extremely directional: layout almost othogonal to the prevailing directions

In the sporadic case of wind blowing parallel to the layout, the small inter-distance

may induce anomalously high loads on turbines.

1 2 3 4 5

6 7

8 9

10 11

12 13


Sector Management in WindSim

WindSim : running 2 layouts A) All 13 turbines

B) Curtailed layout 7 turbines

Sectorial Curtailment AEP

Turbulence Ieff

A B

Sectorial combination of AEP and IEC

classification parameters results, from

the 2 layouts, in Wind Energy Module


Sector Management: AEP Calculation

Unmanaged WTGs

Layout A) 13 WTGs - NO curtailment Layout A) 13 WTGs - NO curtailment

Layout B) 7 WTGs - CURTAILMENT

Replace sectorial AEPs of the

unmanaged layout, with the ones

obtained in curtailed layout (with wake

effects) in the managed sectors:

NNW- WNW - SSE - ESE

Sum new sectorial net AEPs


Sector Management: AEP Calculation

Managed WTGs

Layout A) 13 WTGs - NO curtailment Layout A) 13 WTGs - NO curtailment

Set to 0 AEPs (both with wake and no wake effects) in the managed sectors:

NNW- WNW - SSE - ESE

Sum new sectorial gross & net AEPs

=0.0 =0.0

=0.0 =0.0

=0.0 =0.0

=0.0

=0.0


Effects of Sector Management on AEP

D AEP= - 0.05%

D Wake(%)= - 0.22(%)


Sector Management : Ieff Calculation

10;

/1

12

1

,

12

1

,,

m

s

sIeff

Ieff

m

j

ji

j

ji

m

ji

i

Ieff

samples

Replace sectorial Ieff (j) with the

ones obtained in curtailed layout

in the managed sectors:

NNW- WNW - SSE – ESE

Unmanaged WTGs

Managed WTGs

Set to 0 Number of Samples in

the managed sectors:

NNW- WNW - SSE – ESE

IEC_Classification.log file from Layout with NO curtailment:


Effects of Wind-Sector Management on Ieff

6 m/s

Results on Ieff are minimally affected by sectorial curtailment, especially for winds

> 5-6 m/s

WTG02


Sector-wise values of Irep

Wind rose (especially for high winds) is highly directional, and the managed sectors

modestly contribute to the statistics of Irep

MANAGED SECTORS

Irep WTG02


Conclusions

In some other cases, in order to reduce fatigue loading on turbines’ components, a

Sector Management could be useful (i.e. layout with low efficiency, straight turbines

rows, orthogonal to prevailing winds, with close spacing).

WindSim

Sector Management

Calculation

In the examined case-study, Sector Management has a modest impact on the high

turbulence intensity.

Why? highly directional wind rose;

managed sectors modestly contribute to the statistics of Ieff

high turbulence values are due to ambient turbulence in the prevailing sectors, as

appears in the measurements of the mast

- Run different Sector Management Strategy solutions

- Easily evaluate AEP and TI for each solution

- Helps to find the optimum balance between loads

on turbines and power production

Since the case-study is based on a short set of data (2 years), customer could

choose to adopt Sector Management to avoid even rare occasions of severe

turbulence that may occur, considering the close distance between WTGs.


Contacts

www.studiorinnovabili.it

e-mail: [email protected]

Ing. Beatrice Pistoni

e-mail: [email protected]

Ing. Luigi Imperato

Corso Vittorio Emanuele II, 282-284 - 00186 Roma

Tel. +39 06 8079555

Fax +39 06 80693106

web: www.studiorinnovabili.it

the use of windsim for detailed site verification analysis

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