wind resource assessment over a complex terrain covered by ... · wind farm design üwind resource...

Nikolaos Stergiannis

[email protected]

Wind resource assessment over a complex terrain covered by forest

using CFD simulations of neutral atmospheric boundary layer

with OpenFOAM

http://nstergiannis.com

mailto:[email protected]

27/04/2017 - slide 1

Ø Oneofthefastestgrowingindustries

Ø EUStrategyonClimateChangefor2020andbeyond

Ø 2015anewrecordyear:annual installationscrossedthe62GW

Globalcumulativeinstalledwindcapacity1997-2015(GWECReport2016)

WindEnergy

Wind resource assessment over a complex terrain covered by forest using

CFD simulations of neutral atmospheric boundary layer with OpenFOAM

IndustrialChallenges

WindTurbineDesign

ü rotoraerodynamics

ü mechanical loads

ü incomingflowfield

WindFarmDesign

ü windresourceassessment

ü wakeinteractionsandlosses

ü CAPEX&OPEX

WindFarmOptimization

ü terraineffects

ü wakeeffects

ü poweroutput

• deficitofwindspeed

• increasing turbulence

WakeEffects

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Totalduration:4years

Aimoftheproject:Developanon-deterministicCFDsoftwareforwindenergy

Keypoints:

• Improvedmathematicalmodelforthewindturbines

• AtmosphericBoundaryLayerovercomplexandflatterrain

• Uncertaintyquantificationonthewindconditions

• Open-sourcesoftware(OpenFOAM)

Finalgoal:

• Accurateandfastsimulationsofonshoreandoffshorewindfarms



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Motivation

growth of wind sector

scarcity of available land

wind energy installation on complex terrain is expected to increase

low-cost industrial models fail in very complex sites

inaccurate energy estimation

a crucial process for the successful development of a wind farm project

Wind resource assessment



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• 70% covered by thick forest

• trees of 15 to 20 m height

• mainly neutral stratification

• unidirectional wind from ESE

Site under investigation



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Wind Mast 2

Wind Mast 1



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Wind Mast 2

Wind Mast 1

Wind direction



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NW




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Computational domain

generated with

blockMesh

snappyHexMesh

final mesh characteristics

18 blocks

7.7Mi cells

6km x 6km x 3km

3 layers

1st cell height = 0.9m



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Governing equations & boundary conditions

neutral ABL stratification

homogeneous flow

local equilibrium of k and ε

assumptions*

* Richards, P. J., Hoxey R. P. Appropriate boundary conditions for computational wind engineering models using the k-ε turbulence model. 1993



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Initial conditions

* Troen, I., Lundtang Petersen, E.: European Wind Atlas. 1989

terrain surface characteristic*

forest canopy: z0 = 0.8 m



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Numerical modelling

Incompressible steady state solver

simpleFoam

Turbulence modelling

RANS

modified k-ε turbulence model

* Prospathopoulos J. M., Politis E. S. and Chaviaropoulos P. K.: Modelling wind turbine wake in complex terrain.

2nd order numerical schemes

5000 iterations in total

solution converged in 1500 iterations

10 hours on 16 CPUs of 3.3GHz

Model coefficients *

WM-1

2.698WM-1

CFD

3.759

WM-2

2.545

WM-2

CFD

3.603

0

40

80

120

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Height[m

]

Axialvelocity[m/s]

WM-1at78mheight WM-1CFDsimulations




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Preliminary results and discussion

CFD: 0.156 m/s

Observations: 0.153 m/s

Velocity difference

WM-1

2.698WM-1

CFD

3.759

WM-2

2.545

WM-2

CFD

3.603

0

40

80

120

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Height[m

]

Axialvelocity[m/s]





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Preliminary results and discussion

CFD: 0.156 m/s

Observations: 0.153 m/s

Velocity difference

agreement in the absolute values is much less…



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Conclusions

Test case over a very complex site

Terrain covered with dense forest canopy

Neutral stratification and constant roughness have been assumed

CFD simulations were capable to predict the velocity difference between wind masts

Absolute values were not correct since the profile of WM1 used at the inlet

Challenge

Impose the correct inlet conditions to derived the desired profile at the WM1 location

use a flat terrain before?

use mesoscale models?



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Future work

Simulate over different wind sectors and compare with observations

Include the local roughness map with non-uniform roughness length z0

Use mesoscale model to predict the inlet conditions

Compare with MeteoDyn

“Apersonwhonevermadea

mistakenevertriedanythingnew”

AlbertEinstein

[email protected]

[email protected]



27/04/2017 - slide 14

¿ QUESTIONS ?

wind resource assessment over a complex terrain covered by ... · wind farm design üwind resource...

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