Windfarm Flow Modelling Using Cf d

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2011 ANSYS, Inc. May 8, 20121

Wind Farm FlowModelling Using CFD

2012 Update Webinar

Christiane Montavon, Ian Jones

ANSYS


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2011 ANSYS, Inc. May 8, 20122

15:00 Introduction to the webinar and ANSYS

15.10 Presentation

Why CFD Simulation?

Validation and technical advances

Overview of ANSYS CFD tools for wind farm flow modelling

15.45 Software Demonstration Automated workflow for wind farm modelling

16.05 Question and Answers

16.15 Close

Agenda


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2011 ANSYS, Inc. May 8, 20123

Carbon Trust, project CT090-091, Power from OnshoreWind Farms, and partners,

RWE, Scottish Power, SgurrEnergy

Carbon Trust OWA Phase 1 and partners

(Dong, RWE, Scottish Power, SSE Renewables, Statoil,Frazer-Nash).

SSE Renewables

E.ON

EU BREIN project

Loughborough University

University of Strathclyde...

and many more

Acknowledgements


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2011 ANSYS, Inc. May 8, 20124

Site selection, land and

sea

Generator and shaft design

Wind farm configuration for

optimal power generation

Blade design

Rotor sizing

and acoustics

Tower design

and FSI

Offshore Installation and

certification

ANSYS:A Comprehensive Simulation Platform

Electric Machine

Transformer

Power Distribution

Speed Sensor

Electromechanical

Component

Power Electronic


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2011 ANSYS, Inc. May 8, 20125

More and more onshore sites developed in complex terrain and

complex forestry environment.

Associated risks:

Separation, negative shear exponent factors

Increased turbulence

implications for turbine longevity and energy output

On such sites, standard industry tools (linearised models) used outside

of the envelope where they are meant to operate

Large array losses, particularly so offshore

Empirical models tend to underestimate the losses for large arrays

Atmospheric stability significantly affects array efficiency (e.g. L. Jensen, EWEC

proceedings, Milan 2007)

CFD models increasingly advocated to address these issues.

Need for fidelity of solution and reliability validation!

Need for automated solution for users without CFD background

Background


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2011 ANSYS, Inc. May 8, 20126

N-S Solvers vs. Linearised models

Advantages of Navier-Stokes solvers as

compared to linearized models:

Accurate prediction of turbulence:

- flow turbulence is modeled or resolved using RANS/LES

Better prediction of multiple-wake effects

- accurate geometry description and wake prediction from

multiple installations

- no limit to number of wind turbines considered

Separation/shade effects due to complex terrain- complex terrain is resolved

- shading effects, recirculation and separation are captured

Ref. 2

Ref. 1

Ref. 1

1. Barthelmie, R.J et al., Modelling and measurements of wakes in large wind farms, Journal of Physics: Conference Series 75 (2007) 012049.

2. Barthelmie, R.J et al., Modelling Uncertainties in power prediction offshore, IEA, Risoe, March 2004.


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On range of sites

Onshore: Blacklaw, An Suidhe, Nant y Moch, Harestanes

Offshore: Horns Rev, North Hoyle

On range of issues

Complex terrain

Complex forestry

Stability

Wake interaction

Some done by our users

Offshore: Burbo Bank, Gunfleet Sands, Barrow (DONG

energy)

Forestry: Loughborough University

Validation material

CFD delivers increased accuracy and insight in flow conditions


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ExampleBlacklaw Power Prediction

Complex forestry

Significant wake effects

Good prediction of normalised power

output

RMSE for power prediction over all

turbines and over both masts is 8.5%

R. Spence, C. Montavon, I. Jones, C. Staples, C. Strachan, D.

Malins, 2010, Wind modelling evaluation using an

operational wind farm site,

http://www.ewec2010proceedings.info/allfiles2/517_EWEC

2010presentation.pdf


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Forestry model (resistive model)

Variable forestry height

Variable loss coefficient

Wake Model, large array losses

Horns Rev, North Hoyle

Atmospheric stability accounted for via equation for

potential temperature, buoyancy effect in turbulence

model

Harestanes, An Suidhe

Horns Rev

Technical Advances


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Resistive Canopy Model

available:

Svensson

Lopes da Costa

Katul

Resistance in momentum only

Canopy Input Data

From roughness data

CFX Interpolation Table

variable tree heights

Forestry loss coefficient

Constant or variable with height

Forest Canopy Model

Max Forestry Loss Coef

Height Max

Galion Lidar data

CFD

Flow separation off forested region

C. Montavon, I. Jones, D. Malins, C. Strachan, R. Spence, R. Boddington, 2012, Modelling of wind speed and turbulence intensityfor a forested site in complex terrain, EWEA 2012, Copenhagen.


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2011 ANSYS, Inc. May 8, 201211

Horns RevResults at Hub HeightSector 280

Horizontal velocity Turbulence intensity

Uref= 8 m/s at 70m, z0= 0.0002mWind direction: sector 280


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2011 ANSYS, Inc. May 8, 201212

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10NormalisedPower

Turbine Group

10m/s 270 2 bin

ANSYS CFD

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10

Normalis

edPower

Turbine Group

10m/s 270 10 bin

ANSYS CFD

Data - UpWind

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10

Normalis

edPower

Turbine Group

10m/s 270 30 bin

ANSYS CFD

Data - UpWind

Horns Rev

Normalised Power Down a Row

Simulations by step of 1 degree, sector 270285, averaged for three different bin sizes.

Reasonably good prediction

Tendency for over-estimation of array losses

Good prediction of slope down the row

Consistent for various bin sizes

Upwind data from WakeMeasurements Used in the Model Evaluation. K.S. Hansen, R. Barthelmie, D. Cabezon and E.

Politis. Upwind Wp8: Flow; Deliverable D8.1 Data. 18 June 2008.


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2011 ANSYS, Inc. May 8, 201213

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5

Norm

alisedPower

Column

10 deg bin

ANSYS CFD

Measured Data

Upper 25%

Lower 25%

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5

Norm

alisedPower

Column

30 deg bin

ANSYS CFD

Measured Data

Upper 25%

Lower 25%

North Hoyle

Normalised Power Down a Row

Very good agreement with power data for both bin sizes

Absolutely blind test case!

Uref= 10 m/s at 67m, z0= 0.0001m, upstream TI = 7%Wind direction: sector 260

C. Montavon, S.-Y. Hui, J. Graham, D. Malins, P. Housley, E. Dahl, P. de Villiers, B. Gribben, 2011, Offshore Wind Accelerator:

wake modelling using CFD, EWEA 2011, Brussels.


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2011 ANSYS, Inc. May 8, 201214

Improved results with atmospheric stability

Atmosphere on average stable

above boundary layer

Including this effect

Changes the relative distribution of

the wind speed between hill topsand valleys improves mast tomast cross prediction when masts

located in different type of

positions (i.e. hill tops vs valleys)

Improves the prediction of the

relative TI on site

Including surface stability effects

significantly affects the predictionof array losses

C. Montavon, C. Staples, C. Weaver, 2011, Simulating the flow conditions over complex terrain with RANS models: sensitivity to

a selection of parameters including atmospheric stability , EWEA 2011, Brussels.

C. Montavon, I. Jones, D. Malins, C. Strachan, R. Spence, R. Boddington, 2012, Modelling of wind speed and turbulence intensity

for a forested site in complex terrain, EWEA 2012, Copenhagen.


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2011 ANSYS, Inc. May 8, 201215

4 masts on site, 3 near hill tops, 1 in a location with difficult flowconditions (valley, proximity to forestry)

Cross prediction done for 3 masts with long concurrent time series

Harestanes, Masts on site

All masts with data at 70m, 60m,40m, 30m

Hill top masts:

Holehouse Hill

Hareshaw Rig

Valley mast:

Bran Rig

Hareshaw Rig

Holehouse Hill

Bran Rig


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2011 ANSYS, Inc. May 8, 201216

Maximum relative errors in wind speed cross predictions for three model

configurations:

1.Purely neutral

2. Conventionally neutral i.e. stableconditions in free stream, with

potential temperature gradient of US standard atmosphere, and neutralconditions at ground (adiabatic).

HarestanesMast to Mast Cross Prediction (wind speed)

3 masts (70m only) 3 masts (all heights)

Model BRAN-HOL BRAN-HAR HOL-HAR BRAN-HOL BRAN-HAR HOL-HAR

neutral 11.8% 13.3% 1.8% 24.0% 24.0% 3.2%

stable 0.4% 4.1% 5.4% 2.9% 6.5% 6.2%

Improved results with atmospheric stability


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2011 ANSYS, Inc. May 8, 201217

Ongoing validation exercise together with end users,see e.g. our joint EWEA publications at

Copenhagen 2012, available from:

https://docs.google.com/open?id=0B6Cp_fvx8o5Dei0tenVqelZZQzQ

Brussels 2011, available from:

https://docs.google.com/leaf?id=0B6Cp_fvx8o5DMjBkMzQxNWMtOTk

xYy00ZmFiLWFlNzMtZGFhM2U0NWQ1ODFh&hl=en_GB

Previous years, available from:

https://docs.google.com/leaf?id=0B6Cp_fvx8o5DZmEzYzYxMDAtZGYxZi00YmI0LWIwMjYtZWM3NmViYWM2NDI3&hl=en_GB

Validated Tools
https://docs.google.com/open?id=0B6Cp_fvx8o5Dei0tenVqelZZQzQhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DMjBkMzQxNWMtOTkxYy00ZmFiLWFlNzMtZGFhM2U0NWQ1ODFh&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DMjBkMzQxNWMtOTkxYy00ZmFiLWFlNzMtZGFhM2U0NWQ1ODFh&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DZmEzYzYxMDAtZGYxZi00YmI0LWIwMjYtZWM3NmViYWM2NDI3&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DZmEzYzYxMDAtZGYxZi00YmI0LWIwMjYtZWM3NmViYWM2NDI3&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DZmEzYzYxMDAtZGYxZi00YmI0LWIwMjYtZWM3NmViYWM2NDI3&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DZmEzYzYxMDAtZGYxZi00YmI0LWIwMjYtZWM3NmViYWM2NDI3&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DMjBkMzQxNWMtOTkxYy00ZmFiLWFlNzMtZGFhM2U0NWQ1ODFh&hl=en_GBhttps://docs.google.com/leaf?id=0B6Cp_fvx8o5DMjBkMzQxNWMtOTkxYy00ZmFiLWFlNzMtZGFhM2U0NWQ1ODFh&hl=en_GBhttps://docs.google.com/open?id=0B6Cp_fvx8o5Dei0tenVqelZZQzQhttps://docs.google.com/open?id=0B6Cp_fvx8o5Dei0tenVqelZZQzQ


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2011 ANSYS, Inc. May 8, 201218

Beaucage, P., Robinson, N., Brower, M., Alonge, C.,Overview of six commercial and research wake models

for large offshore wind farms, Proceedings EWEA 2012,

Copenhagen.

Garza, J., A. Blatt, R. Gandoin and S.-Y. Hui (2011)Evaluation of two novel wake models in offshore wind

farms . Proceedings from the EWEA Offshore

conference, 29 Nov. - 1 Dec 2011.

Desmond, C., Sayer, A., Watson, S., Hancock, P., Forest

Canopy Flows in Non-Neutral Stability , EWEA 2012,Copenhagen. (poster award).

Clive, P., Dinwoodie, I., Quail, F., Direct measurement

of wind turbine wakes using remote sensing,

Proceedings EWEA 2011, Brussels.

ANSYS CFD Featured In Independent Publications


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2011 ANSYS, Inc. May 8, 201219

WindModeller: set of tools wrapped around

ANSYS standard CFD products:

Allow non-CFD experts to perform wind farm analyses inautomated way

Drive ANSYS CFX or FLUENT flow solver

Allow advanced user to encapsulate their own expertise

(access to customised setup and post-processing scripts which

can easily be altered by the user to further develop the tools )

WindModeller Tools for Automated Solution


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2011 ANSYS, Inc. May 8, 201221

WindModeller: Simulation Process

Wind farm simulation process from user perspective Set up analysis on desktop computer (either via GUI or command line)

Submit job to:

Run possible large number of cases on the local machine or on a remote server

Postprocess results to automatically generate reports/summary data files

Possibility to perform additional post-processing on individual results files using CFDPost

Setup on desktop

Run on local or remote

computer Report as html file


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2011 ANSYS, Inc. May 8, 201222

Current recognised terrain format SRTM, Shuttle Radar Topography

Mission, freely available, 90mresolution (finer resolution in the US)

NTF, National Transfer Format, contourdata (UK)

.map files (WAsP format) Generic point data file (.csv)

Terrain converted to tesselatedformat (STL)

Meshing with custom tools

Fixed mesh structure, hexahedral mesh(5 or 9 blocks), aimed at processautomation

Template mesh morphed onto STLterrain representation

Variable mesh topology forelongated/twin wind farms

Meshing Approach


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2011 ANSYS, Inc. May 8, 201223

Varying Mesh Topologies

Compact wind farm

Elongated wind farm

Twin wind farms


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2011 ANSYS, Inc. May 8, 201224

User can prescribe:

horizontal resolution in central

region

Rate of horizontally expansion

outside

first layer cell heights in vertical

Good control of mesh resolution in

lower heights (ensures appropriate

resolution is achieved in forested

regions)

Smooth vertical expansion above

Meshing Controls


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2011 ANSYS, Inc. May 8, 201225

Mesh Adaption on Wind Turbine Rotor

Improve resolution by automatically refining mesh around the turbine

location, from the specification of the rotor location and actuator diskparameters only

Automatically enabled if wake model is used.

Initial mesh 1strefinement

2ndrefinement

Final mesh


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2011 ANSYS, Inc. May 8, 201226

Outer surface divided into 24

regions

12 for inlet b.c. (Dirichlet on

velocity)

12 for outlet b.c. (entrainment

conditions with prescribed static

pressure)

Setup automated to run for e.g.

12 wind directions

Selection of surfaces defininginlet/outlet automated in script

running cases for various wind

directions

meshing done only once

Setup


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2011 ANSYS, Inc. May 8, 201227

Flow Modelling in WindModeller

Atmosphere modelled as: incompressible fluid (Air at 15C)

assuming neutral stability

solving for steady state RANS

Turbulence modelled via two-equation model Shear Stress Transport (SST) turbulence model or k- .

Ground modelled as rough wall (spatially variable roughness)

Inlet boundary conditions Classical constant-shear ABL profiles (Durbin & Petterson Reif ):

Additional physics: Forest canopy model(resistive term in momentum equation + additional source

terms in turbulence model)

Multiple wake model(actuator disk model) Atmospheric stability as beta feature

2/1

2

*

C

uk u

uln

z

z

* ( )

0 z

u

3

*


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2011 ANSYS, Inc. May 8, 201229

Simple Wake Model

Wind turbine represented by momentum sink

constant thrust per volume within

identified rotor disk.

Wind turbine orientation parallel towind direction at inlet

Works on any type of mesh, althoughit is expected that the best resultswill be obtained with resolution thatcaptures the wind turbine diskreasonably well

User input:

Coordinates of hub location

WT diameter

WT thrust and power curve


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2011 ANSYS, Inc. May 8, 201230

As part of the automatedapproach WindModeller cangenerate:

Plots of streamlines

Identification of recirculation zones

Plots at constant height AGL andprofiles at wind turbine/mastlocations for quantities such asnormalised velocity, turbulenceintensity, shear exponent factor

Exported data tables of similarquantities at wind turbine/mast

locations Export to Google Earth (.kml files)

Automated report in html format

Post-Processing in WindModeller


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2011 ANSYS, Inc. May 8, 201231




Plots at constant height AGL andprofiles at wind turbine/mastlocations for quantities such asnormalised velocity, turbulenceintensity, shear exponent factor

Exported data tables of similarquantities at wind turbine/mast

locations Export to Google Earth (.kml files)




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2011 ANSYS, Inc. May 8, 201232




Plots at constant height AGLandprofiles at wind turbine/mastlocations for quantities such asnormalised velocity, turbulenceintensity, shear exponent factor,flow angles

Exported data tables of similar

quantities at wind turbine/mastlocations

Export to Google Earth (.kml files)




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2011 ANSYS, Inc. May 8, 201233




Plots at constant height AGL andprofiles at wind turbine/mastlocations for quantities such asnormalised velocity, turbulenceintensity, shear exponent factor ,flow angles







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2011 ANSYS, Inc. May 8, 201236








Automated report in html format,including the above



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Automated report in html format,including the above



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2011 ANSYS, Inc. May 8, 201238

Wind Data Transposition Module

Simulations establish climatological relationships between wind conditions at

mast (reference site) and WTG (predicted site).

Simulations are performed independently from the data collection at the mast.

Data collected at mast

Wind conditions

predicted at WTG

Wind data transposition module


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2011 ANSYS, Inc. May 8, 201239

Energy Assessment/Cross Prediction

Wind data for input:

Time series or Frequency tables

Allows for multiple masts and with

/ without wake calculations

Can deal with heterogeneous wind

farm Masts data collected before or

after wind turbines installed

Possibility to do a post-

mortem on an existing wind

farm to understandperformance issues of single

WT if mast still measuring

when wind farm is operational

Note: masts must be within simulation domain

(no MCP)


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2011 ANSYS, Inc. May 8, 201240

Output from Data Transposition

Tables of Capacity Factors (bydirections and overall) summarising

the average annual energy output at

each WT.

Wind speed distributions (WAsP .tab

files) at WT and masts.

Resource file (WAsP .rsf) at WT

locations.

Summary table with average wind

speed at masts from cross prediction.

Summary tables of mean andrepresentative turbulence intensity by

wind speed classes at masts and WTlocations. (when working from time

series, including the wind speed

standard deviation as input).


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2011 ANSYS, Inc. May 8, 201241

Customised tools based on standard ANSYS CFDsoftware under continuous development

Driven by customer and project demands

Used on many cases

Made available to customer on service based

approach via two stage process:

1stphase: demonstration of capability on terrain chosenby customer

2ndphase: Technology Transfer. Tools made available tocustomer, also includes one-to-one training, support

and maintenance of the tools after delivery.

Develop features on request.

Availability of WindModeller Tools


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2011 ANSYS, Inc. May 8, 201242

OWA Phase II: integration of atmospheric stability andassociated effects on large array losses

Carbon Trust POWFARMM project: complex terrain,forestry, wakes, comparison with masts and Galion

LIDAR dataVarious consultancy projects recently completed for

customers

Pollution transport

Integration of buildings

More complex stability conditions (e.g. strong inversions,coastal low level jets)

Diversification into modelling of marine arrays

(TideModeller)

Ongoing Projects


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2011 ANSYS, Inc. May 8, 201243

CFD delivers increased accuracy for

Complex terrain/complex forestry cases

Estimation of large array losses

Atmospheric stability improves accuracy compared to

neutral cases, which tend to be used by other CFDpackages in the industry

ANSYS has a suite of tools (WindModeller) that helpsyou automate the simulation process, with state of the

art models for

Forestry Wakes

Atmospheric stability

Validation material available to attest this.

Summary


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Windfarm Flow Modelling Using Cf d