EWEA 2011 – Brussels – 16 March 2011

B. Conan, EWEA 2011, Brussels 1 / 21

EWEA 2011 – Brussels – 16 March 2011

Feasibility of Micro Siting in Mountainous Terrain by Wind Tunnel

Physical ModelingB. Conan1,2,

S. Buckingham3, J. van Beeck1, S. Aubrun2, J. Sanz Rodrigo4

(1) von Karman Insitute for Fluid Dynamics, Rhode-Saint-Genèse, Belgium

(2) Institut PRISME, Université d’Orléans, France

(3) CENAERO, Belgium

(4) CENER, National Renewable Energy Center, Wind Energy department, Spain


The WAUDIT project

• Wind Resource Assessment Audit and StandardizationEuropean Commission Marie-Curie Initial Training Networks

Pool of 18 PhD FP7-PEOPLE-ITN-2008


Physical modeling of atmospheric flows

Pollution dispersion

Pedestrian comfort: European parliament

Aerodynamic design of the Belgium polar station

Wind loading on buildings


Physical modeling assumptions

• Modeling requirements (N-S equations):– undistorted scaling geometry

– equal dimensionless inflow conditions

– Ri (Richardson)

– Ec (Eckert)

– Pr (Prandtl): same fluid

– Ro (Rossby): Coriolis effect neglected in the near surface

– Re (Reynolds): cannot be conserved• Ensure fully turbulent state: Re > 10 000

• Minimum roughness Reynolds number:

• Reynolds number dependency study if possible

cst. temp. wind tunnel neutral stratification

5. 0* zu

R criticale


Modeling assumptions

• Modeling questions common to CFD and physical modelers:– reproduction of atmospheric inflow conditions

– choice of the modeling area

– choice of surface roughness / wall function

– integration of the model in the domain

• Specific topics for physical modeling: – Re number dependency

– high scaling factors

– choice of the measurement techniques


• Alaiz mountain, Pamplona, Spain:

– 1 130 m high (600 m)

– very complex terrain

– steep slopes

– dominant North wind

– upstream ridge > 200m

CENER - Test Case


• Mock-up in the wind tunnel:– 1 / 5000 scale (2.8 m wide x 3 m long)

– one direction tested

CENER - Test Case

Model realized by UPM (Universidad politechnica de Madrid, Spain)


Modeling inlet conditions

• Parameters to reproduce:– velocity profile

– roughness length ( )

– friction velocity ( )

0*ln.

1zZ

uU

0z

*u



• ABL generation:– grid

– fence

– adaptative roughness elements



• Parameters to reproduce:– velocity profile

– roughness length ( )

– friction velocity ( )

– turbulent profiles (3 components)

– turbulent spectra

Need for 3 components time resolved measurements

0*ln.

1zZ

uU

0z

*u


• Triple hot-wire probe– punctual measurement

– U, V, W, u, v, w, u’, v’, w’

– Iu, Iv, Iw

– TKE

– shear stress:


''.* vuu2*.uw



• Alaiz inlet conditions:

Wind tunnel can model different roughness length and scales Inflow reproduction challenging at very high scaling factor


Particle Image Velocimetry (PIV)

– 2D instantaneous velocity field (U, W)

– high spacial resolution: 150mm x 150mm with 2mm = 10m resolution

– 500 images to perform averaging


Particle Image Velocimetry (PIV)

• Averaged fields:– velocity field

– turbulence intensity

– velocity vector

• Instantaneous fields:– velocity field

– shear stress

– vorticity

– vortex detection


• PIV:– space resolution

– 2 components

• Hot-wire:– time resolution

– 3 components

Complementary measurement techniques

High wind potential areas detection by PIV Fine characterization of the wind profile with triple hot-wire

Measurement error:

Measurement error : PIV: 1.5%

HW: 2%

Statistical error:

Averaged quantities: PIV: 1.5% (95% c.l.)

HW: 1% (95% c.l.)

Fluctuating quantities: PIV: 8% (95% c.l.)

HW: 6% (95% c.l.)


Flow around the mountain

• Velocity field:– speed-up at the top of

the mountain

• Turbulence intensity:– inlet perturbation

– influence at mountain’s top

• Velocity vector field:– perturbation of the

inlet velocity profile

– speed-up at mountain’s top



• Fractional Speed-up Ratio at 90m (FSR): ref

refii U

UUFSR

Reference velocity

Max speed up

Speed-down due to the mountainRecovery from the influence of the ridge



• Comparison 2D CFD simulation:

50% speed-up at the mountain’s top High influence of the front ridge

From: D. Munoz-Esparza et al. EWEA 2011, PO. 218


Conclusions and future investigations

• Inflow conditions modeling:– the wind tunnel can model different ABL, it is more challenging at

very high scaling factors. characterization of all the inlet conditions possible to model in the

wind tunnel.

• Choice of the modeling area:– a ridge of 1/3 of the main mountain height and situated 4km

upstream influences a lot the FSR. parametric study with simplified geometries


Conclusions and future investigations

• Measurement techniques:– combination of PIV and triple hot-wire very powerful. implementation of Stereoscopic PIV (2D-3C) on Bolund

• Remaining questions:– model roughness implementation Alaiz

– comparison with field data Alaiz

– Reynolds number dependency

• Quantification of the influence of each parameter


Thank you for your attention

References:[1]. Cermak, J.E. “Laboratory simulation of the Atmospheric Boundary Layer” AIAA Journal

vol. 9 num. 9 pp1746-1754 (1971).

[2]. Sanz Rodrigo, J., Van Beeck, J. and Dezsö Weidinger, G. “Wind tunnel simulation of 1the wind conditions inside bidimensional forest clear-cuts. Application to wind turbine siting” J. Wind Eng. Ind. Aerodyn. 95(7)609-634, 2007.

[3]. Siddiqui, K., Hangan, H., Rasouli, A. “PIV technique implementation for wind mapping in complex topographies” Meas. Sci. Technol. 19 (2008) 065403 doi:10.1088/0957-0233/19/6/065403.

[4]. ESDU Engineering Science Data Unit. Characteristics of atmospheric turbulence near the ground. 1985.

[5]. VDI-guidelines 3783/12, 2000. Physical modelling of flow and dispersion processes in the atmospheric boundary layer – application of wind tunnels. Beuth Verlag, Berlin

[6]. Raffel, M., Willert, C., Wereley, S. “Particle Image Velocimetry: a practical guide” Springer Verlag, 2007

[7]. Bruun, H.H., ”Hot-wire anemometry” Oxford University Press Oxford (2002) ISBN: 0198563426


The WAUDIT project

• Wind Resource Assessment Audit and Standardization

EU program: Marie-Curie Initial Training Networks Action

FP7-PEOPLE-ITN-2008

– Scientific/Technical:

Advance the state-of-the-art on wind assessment

– Academic:

Provide a multidisciplinary education around wind energy with specialization on wind resource assessment (18 PhDs)


Back-up

• Modeling requirements (N-S equations):

forcesInertialforcesBoyancy

Ri

ydiffusivitThermalydiffusivitMomentumPr onacceleratiCoriolis

onacceleratilocalRo

forcesviscousforcesInertialRe

enthalpyenergykinetic

Ec


Back-up

• Pressure gradient

• Fully developed flow– Two profiles at X and X+2m

05.0.

2

.

2

U

dXdP

a

0dXdU


Back-up


3

2

1

2

2

21

22

22

22

23

22

21

44

33

2210

.

cossin.sincos.sin

0cossin

sinsin.coscos.cos

.

1

1

1

....

X

X

X

W

V

U

U

U

U

kh

kh

hk

X

X

X

EPEPEPEPPU

III

II

I

i

eff

eff

eff

IIIIII

IIII

II

iiiieff

Back-up

Calibration with a 4th polynomial:

Velocity components in the frame of the wires:

Velocity in wind tunnel frame:


Modelling boundary conditions

Velocity in wind tunnel frame:


Back-up


• PIV:– space resolution

– 2 components

• Hot-wire:– time resolution

– 3 components

Back-up

High wind potential areas detection by PIV Fine characterization of the wind profile with triple hot-wire

Measurement error:

Measurement error : PIV: 1.5%

HW: 2%

Statistical error:

Averaged quantities: PIV: 1.5% (95% c.l.)

HW: 1% (95% c.l.)

Fluctuating quantities: PIV: 8% (95% c.l.)

HW: 6% (95% c.l.)


Back-up

Assessment of wind potential in complex terrain with high accuracy

– field measurements: reality, but long, expensive and low resolution– linear models: limited to slopes < 30%– numerical simulation: (main area of research) high resolution, controlled boundary

conditions, modeling all scales but also high level of modeling: need for precise validation

Wind tunnel modeling:– constant conditions– space and temporal resolution– moderated level of modeling

• Example on a mountainous terrain

EWEA 2011 – Brussels – 16 March 2011

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