Wind Lidar measurement optimization in complex terrain

transcript

Thursday. 22 April 2010

Wind Lidar measurement optimizationin complex terrain

Matthieu Boquet, Laurent Sauvage, Rémy Parmentier, Jean-Pierre Cariou - LEOSPHERE/NRGFerhat Bingöl – Risø DTUDimitri Foussekis – CRES

Armand Albergel – Aria TechnologiesGuillaume Dupont – MeteodynCatherine Meissner – WindSim

Thursday, 22 April 2010

Agenda

Introduction: complex terrain requirementsWind Lidar volume measurement vs. cups point measurement: assumptions for direct comparison and validity of these assumptionsCFD modeling and WindCube measurement process simulationGeometrical optimization and CFD combination for improving Lidar measurement in complex terrainsConclusions

Wind Resource Assessment Program

Estimate the wind speed distribution:On-site measurement: masts and remote sensorsMeteorological stations and airports recordsFlow modeling software to extend measurements both in space (hub height and turbines location) and time (long-term scaling)

In complex terrain:Requires more on-site measurement locations to gain certainty in the WS estimation

A remote sensor is a precious complementary system:

But performances need to reach cup standards, i.e. bias<2%

Pulsed Wind Lidar principleHOW AND HOW WELL DOES THE WINDCUBETM RETRIEVE WIND VELOCITY VERTICAL PROFILES?

Lidar volume measurement principle

1) Pulse length and beam width

2) Conically scanning Probed volumes are

away one from another

3) Sequentially scanning

Radial velocities measurement

vrad = v.axisbeam

qLaser shooting direction

aerosols

Radial velocity is the projection of aerosols velocity on laser beam axisFlow homogeneity assumption: aerosols velocity is the same at every radial velocity measurement locationU, V and W can be resolved

Flat Moderately complex Mountainous

Terrain complexity influence

Lidar + mast

Forest

Terrain slope 10°

Wind direction

South-East:

Plateau, no trees

North-West:

10° slope, trees

At 80m Slope = 1.024

Slope = 0.988

Intercomparison of Horizontal wind speed at 78mN±40deg

y = 0.9627x - 0.2066R2 = 0.9911

y = 0.9457xR2 = 0.9907

0 4 8 12 16 20Cup Anemometer [m/s]

At Risø test site Høvsøre

(onshore 1st phase of Norsewind Project)

Observed relative

difference:~1%

Observed relative

difference:~2%

Observed relative

difference:~6%

CFD Modeling analysisUSING A CFD MODELING TO BETTER UNDERSTAND THE LIDAR AND ANEMOMETER DIFFERENCES IN COMPLEX TERRAIN

Complex Spanish site

North-West wind

MERCURE/Aria TechnologiesCFD model adapted to complex topographyStationary CFD: A study of Lidar wind velocity retrieval process under various distorted flow conditionsSimulation of Lidar measurement process with MatLab

Met mast

WindCube

North-West wind

Lidar vs. cup simulation

Lidar overestimation >5%

Lidar underestimation <-5%

North-West Wind

Terrain elevation represented with colorsBlack stars: locations of Lidar and cup measurement simulation

CFD simulation On site measurement

-5.8% -6.1%

Horizontal gradient of vertical wind speed dependency

Lidar-cup relative difference vs. horizontal gradient of the horizontal wind speed No dependency

Lidar-cup relative difference vs. horizontal gradient of the vertical wind speed Clearly correlated

Geometrical OptimisationHOW CAN WE MODIFY THE LIDAR MEASUREMENT PROCESS TO GET CLOSER TO CUP?

Reducing the scanning cone ?

Probing a smaller volume then more homogeneous ? No! At a given height, difference depends only on

horizontal gradient of vertical wind speed

No magical scanning cone angleDangerous below 15° and above 30°

U UUW1 W2 W3

Radial vel.

Radial vel.Source of Bias

30° vs. 15° - CRES data

y = 0.9627x - 0.2066R2 = 0.9911

y = 0.9457xR2 = 0.9907

y = 0.9457xR2 = 0.9871

30° cone angle 15° cone angle

Adding more lines of sight ?

Consider first order variation of wind speedAs new unknown variables are introduced, one should add new Lidar equations to retrieve themHowever, a line of sight LOSi gives the radial velocity Si:

No LOS brings info on Wi

Lidar-CFD combinationCOULD A CFD MODEL BRING THE MISSING INFO?

Using a model to correct Lidar data

Model can provide the essential site specific info on the vertical wind speed distribution to correct Lidar data

Modeling

Relative difference on site Relative difference with corrected Lidar

Methodology validation

Meteodyn WT and WindSim correction add-on tested on 2EN and CRES WindCubes on complex Greek site

CFD combination gets the bias from 6% down to 1%

Conclusion

Point and volume measurement leads to wind speed value differences in complex terrainVertical wind speed loss of homogeneity is the main source of errorScanning cone angles between 15°-30° act similarly for horizontal wind speedMore lines of sight are not more useful infoMeteodyn WT and WindSim add-on:

WINDCUBE® Lidars data are now quantitatively useable on all types of

terrain

Questions ?www.leosphere.com

mboquet@leosphere.fr

Wind Lidar measurement optimization in complex terrain

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