EWEC06 (2006.2.28, Athens) Numerical Site Calibration on a Complex Terrain and its Application for Wind Turbine Performance Measurements Toshiyuki SANADA (Mechanical Engineering Science, Kyushu University, Japan) Masatoshi FUJINO Daisuke MATSUSHITA Takanori UCHIDA Hikaru MATSUMIYA Masao WATANABE Yoshinori HARA Minori SHIROTA Standardization research of wind turbine in Japan Supported by NEDO (New Energy Development Organization)

Outline 1 Numerical Site Calibration A pair of masts EWEC06 (2006.2.28, Athens) Outline 1 A pair of masts Numerical Site Calibration Reference meteorological mast Wind Speed at a wind turbine Wind speed CFD (Computational Fluid Dynamics) Meteorological mast Fluid Dynamics Lab, Kyushu University

Outline 2 Flow Correction Factor due to Complex Terrain LES EWEC06 (2006.2.28, Athens) Outline 2 Flow Correction Factor due to Complex Terrain LES Prediction of wind speed GIS Meteorological mast Wind Turbine Performance Measurements

~ Wind Turbine in Japan ~ Introduction ~ Wind Turbine in Japan ~ Renewable energy 1.35% of total electricity supply(2010) Ratification of Kyoto Protocol Renewable Portfolio Standard (RPS) Law 　 Wind power almost 1/10 of Germany’s !! March, 2004 926 MW 2010 3,000 MW (the official government target) 2030 11,800 MW (the new target of JWPA) Challenges for Japanese wind turbine development Complex terrain, Typhoon, Turbulence, Gust, Thunder storm …

~ Wind Turbine in Japan ~ Introduction ~ Wind Turbine in Japan ~ Wind Turbines in Japan Complex Terrain for Japanese wind turbine development mountain area 73% planes 14% 50% of the people live in plains. Wind Turbine Performance Measurements at Complex Terrain for next step… Prediction of wind power generation

Performance Measurements Introduction Performance Measurements IEC61400-12-1 Example wind speed at reference mast　　 = wind speed at wind turbine wind speed not influenced by wind turbine requirement of high accuracy in measuring wind speed

Site Calibration Complex Terrain Introduction Site Calibration Complex Terrain Flow correction factor b (=the wind speed at the wind turbine location divided by the wind speed at the meteorology mast) Test site requirements (topographical variations) ・Maximum slope <5%　（between 2L and 4L） ・Eliminate the direction > 0.02 in b between neighboring sector ・Each wind direction bin, no larger than 10° V1=bV2 IEC61400-12-1

Site Calibration Japan Introduction Site Calibration Japan Wind Turbine Performance Measurements Imamura et al. (EWEC01) Complex terrain that fails to satisfy the IEC standard Two points correlation analysis (before WT is constructed) Correlation equation using 10miniuts average. Direction with high correlation (eliminate the direction with high turbulent intensity) After measurements…., If there is no direction with high correlation? COST RISK

Objective To propose a numerical site calibration, which employs CFD for wind field simulation over a complex terrain to evaluate flow correction factor.

Methods To measure the wind speed at reference mast Measurements Numerical Analysis Methods To measure the wind speed at reference mast To calculate the flow correction factor b using CFD To correct the wind speed using b To evaluate the wind turbine performance V1=bV2 V1=bV2

Numerical Analysis Nonlinear, Unsteady simulation ! RIAM-COMPACT (Uchida & Ohya, 1999, 2003) Grid scale vortex : Navier-Stokes Eq. Sub-grid scale vortex : model LES (Large Eddy Simulation) Nonlinear, Unsteady simulation ! time series analysis correlation turbulent intensity etc…

finite-difference method Numerical Analysis coordinate system generalized curvilinear coordinate variable arrangement collocated arrangement discretization method finite-difference method coupling algorithm fractional step method time advancement method Euler explicit method poisson equation for pressure SOR method convective terms 3rd-order upwind scheme based on an interpolation method (a=0.5) other spatial derivative term 2nd-order central scheme SGS model Smagorinsky model + wall damping function boundary condition inflow 1/7 power low top and side free-slip outflow convective outflow ground no-slip

Digital Map Wind turbine performance measurements Numerical simulation of wind turbine scale Digital map of wind turbine scale c.f. GSI map (50m, most commonly used) GIS (Geographic Information System) technique aero-photograph Printed atlas aero-photograph CAD data

Computational Grid 160 x 160 x 60

Test Site ~takashima~ N topographical variations Point Distance Height difference Mean slope O-A 50m 25m 50% O-B 75m 33% O-C 62.5m 40% Distance Maximum slope <2L <3% ≥2L and <4L <5% ≥4L and <8L <10% fails to satisfy the IEC standard : test site requirement site calibration

Measurements Spatial configuration of WT & mast N L=5.13D mast1: reference mast mast2: for validity check

Wind Characteristics NW, N, S mast1 mast2 1st, April, 05 ~ 30th, November, 2005 Wind Rose Average Wind Speed Average Turbulent Intensity [%] [m/s] [%] N NW, N, S

How to define the flow correction factor b ? M1 Example, North wind Condition: 5m/s, 10m/s, 15m/s, 10minuts time series of wind speed of each points z=M1 mast 1 WT

How to define the flow correction factor b ? 10 minutes averaged value (corresponding to 10 minute data set) regression line (minimum mean square method)　 correlation coefficient : high However … Uncertainly analysis

Uncertainly analysis Correction Factor mast 1 WT (a) (b) Assumption: bivariate normal distribution u=N(0, s2): component of variation from average wind speed

How to define the flow correction factor b ? confidence interval 95% (±1.97s) evaluation of correction factor b error of UWT In this case, a=21% High accuracy in measuring wind speed is required. The power is approximately proportional to wind speed to the third power.

Flow Field Results ~ NORTH WEST ~ N NW y=WT y z M2 M1 WT Mast1 & WT: flow smooth mast2: large Uz components y=M2

Flow Correction Factor Results ~ NORTH WEST ~ N NW Flow Correction Factor regression analysis b=1.059 a=0.6% Good direction for WT performance measurements

Validity Check Results ~ NORTH WEST ~ N NW validity check : mast 1 & mast 2 Measurements (10min data-set) Calculation cup vs. cup over estimation? y=M2

Results ~ NORTH ~ N Flow Field Flow Field M1 M1 WT WT z=mast1 z=mast1

Flow Correction Factor Results ~ NORTH ~ N Flow Correction Factor regression analysis b=1.2241 a=21% Poor direction for WT performance measurements

Results ~ SOUTH ~ N S Flow Field Flow Field M1 WT y=WT z=WT WT

Flow Correction Factor Results ~ SOUTH ~ N S Flow Correction Factor regression analysis b=1.0844 a=1.0% Good direction for WT performance measurements

Validity Check Results ~ SOUTH ~ What happen at the Mast 2 ? Turbulent Intensity WT M2 Siting of Meteorological mast a=53.0% !!

Power Performance ~ NORTH WEST ~ NW

Power Performance ~ NORTH ~

Power Performance ~ SOUTH ~

Conclusion A site calibration by employing CFD (LES and detail digital map obtained from GIS) is proposed. A numerical site calibration can evaluate directional flow correction factor. A numerical site calibration can be applied to the wind turbine performance measurements if terrain condition and flow direction are carefully chosen. Using numerical simulation, the appropriate direction and position of meteorological mast for site calibration where fluctuation of wind speed is small, can be chosen.

For Future Numerical site calibration at other sites. (validity check) Measurements of wind turbine performance at complex terrain (effects of flow distortion, turbulent intensity) (For Japanese wind turbine development, a performance testing of WT at complex terrain is required for prediction of electric power generation)

Validity Check Results ~ NORTH ~ N validity check : mast 1 & mast 2 Measurements (10min data-set) Calculation Measurements: north wind at mast1 = Calculation : north wind into island

Validity Check Results ~ SOUTH ~ N S validity check : mast 1 & mast 2 Measurements (10min data-set) Calculation Qualitatively good agreement