Experimental and Computational Investigation of

Flow Distortion Around a Tubular Meteorological Mast

Matthew Filippelli - Pawel Mackiewiczmfilippelli@awstruewind.com - pmackiewicz@awstruewind.com

AWS Truewind LLC255 Fuller Road, Suite 274

Albany, New York

CanWEA Conference – Toronto, Ontario – October 2005

IntroductionThe accuracy of wind resource assessments can be affected by the meteorological mast.

Two- and three-dimensional CFD models were created to examine the effects and mitigate induced error

Procedure

• Computational Model Created– 2D and 3D models of tubular met mast were designed– Physical and environmental parameters were chosen

• Model Runs Executed– 2D and 3D models run on Fluent® v. 6.0 CFD software– Numerous case studies were executed to study varying tower

and flow configurations

• Field Measurement Comparisons– Selected long term, well-documented data sets North America– Compared results with several instrumentation configurations

2D Computational Model Parameters• Environmental Parameters: Representative of

common North American monitoring environments• Density: ρ= 1.18 kg/m³• Viscosity: μ= 1.777 x 105

• Turbulence Intensity: ti= 12.5%• Speed: V= 7.5, 11, 15 m/s

• Physical Parameters: Typical met mast dimensions• 6 in (0.1524 m) diameter cylinder • Variable surface roughness• 1.067 m Boom length (7.5 diameters from tower axis)

• Model Parameters• RANS equation based, K-epsilon turbulence model • Mesh Size: ~20,000 cells

2D Case Results: Model Output

Spe

ed R

atio

Flow Direction

Dimensions in Meters

Case 1Dashed line indicates

measurement distance

2D Case Results: Case Comparison

Angular Position (Degrees)

Per

cent

Spe

ed D

evia

tion

0.980

0.985

0.990

0.995

1.000

1.005

1.010

1.015

1.020

0 30 60 90 120 150 180 210 240 270 300 330 360

Case 1Case 2

Case 1: High Roughness Tower

Case 2: Tower w/ Signal Cables

Comparison with Existing Models: Iso-speed PlotRED: Case B CFD Black: IEA and IEC potential flow

Flow Direction

2D Data Analysis:Percent Speed Variation at Standard Instrument Stand-off

Angular Position (Degrees)

2-D model output, normalized total speed

0.85

0.90

0.95

1.00

1.05

1.10

1.15

0 30 60 90 120 150 180 210 240 270 300 330 360

Per

cent

Spe

ed D

evia

tion

2D Data Analysis:Percent Speed Variation for Two Booms (330° and 242°)

Angular Position (Degrees)

Per

cent

Spe

ed D

evia

tion

2-D model output, normalized total speed for two boom directions

0.85

0.90

0.95

1.00

1.05

1.10

1.15

0 30 60 90 120 150 180 210 240 270 300 330 360

2D Data Analysis:Output Ratio between two Booms (330° and 242°)

Angular Position (Degrees)

Per

cent

Spe

ed D

evia

tion

2-D model output, ratio for two boom directions

0.85

0.90

0.95

1.00

1.05

1.10

1.15

0 30 60 90 120 150 180 210 240 270 300 330 360

0.40

0.50

0.60

0.70

0.80

0.90

1.00

010

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160170

180190

200

210

220

230

240

250

260

270

280

290

300

310

320

330

340350

330º

242º

2D Data Analysis:Tower Validation

Angular Position (Degrees)

Per

cent

Spe

ed D

evia

tion

CFD Model and Mid-Tower Data (30 m)

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

0 30 60 90 120 150 180 210 240 270 300 330 360

CFD Model

Tower Measurement (30m)

CFD Case 1

30m Tower Data

3D Computational Model Parameters• Environmental Parameters: Representative of

common North American monitoring environments• Density: ρ= 1.18 kg/m³• Viscosity: μ= 1.777 x 105

• Turbulence Intensity: ti= 12.5%• Speed: V= 7.5 m/s

• Physical Parameters: Tower-top model• 6 in (0.1524 m) diameter hollow cylinder, 6 m total height• Surface roughness 0.15 in (3.81E-3 m)• 1.067 m Boom length (7.5 diameters from tower axis)

• Model Parameters• RANS equation based, K-epsilon turbulence model • Mesh Size: ~70,000 cells

3D Case Results: Model OutputSpeed Ratio for Y-Z Plane

(Flow into Page)Speed Ratio for X-Z Plane

(Flow Left to Right)

Dimensions in Meters

3D Data Analysis:Percent Speed Variation Radially Outward from Tower (Y-Z Plane)

Radial Distance (Tower diameters)

Per

cent

Spe

ed D

evia

tion

3D Data Analysis:Percent Speed Variation Radially Outward from Tower (X-Z Plane)

Radial Distance (Tower diameters)

Per

cent

Spe

ed D

evia

tion

Conclusions• Tower surface irregularities impact flow

at typical instrument stand-offs– Use Longer booms to lower induced error

• Significant 3D flow effects occur ~6 diameters above and below the tower top, but can be avoided – Locate side-mounted booms at least 6

mast diameters below the top– Mount tower-top instruments at least 6

mast diameters above the top

Future Work• Additional model validation against field

measurements • Refinement of CFD model construction

and parameters • Case-specific field or tunnel testing• Develop correction routines for tower

data sets

Thank You