Experimental study of the wake regions in wind farms By: Alaa Hasan Under Supervision of Prof. Ryo Amano

Objective To scan in detail the scenario that takes place behind a single wind turbine model by focusing on three parameters; average main wind velocity component, velocity deficit and total turbulence intensity. The locations of low velocity and high turbulence can be avoided while sitting the subsequent turbine in an inline configuration wind farm. To estimate the distance at which the inlet flow field will restore its original characteristics after being blended through the rotor blades, as it is the distance that should separate two successive turbines in an inline wind farm to guarantee the optimum performance of the second turbine.

Experimental Setup Wind tunnel equipped with VFD suction fan to simulate inflow wind speed. Wind turbine model with 3 blades, 8 inches rotor. Traverse system to move the hot wire probe by means of stepper motors to the exact points at which measurements are done. Data acquisition card to connect the probe and stepper motor to the lab. PC. Hot wire probe of dual sensor type to measure u and v velocity components. Hot wire anemometer to provide 0-5 volts analog output voltage. Hot wire calibrator to convert the voltage signal into velocity. Air compressor to provide compressed air needed for calibration.

Approach

Results – Section Planes

Results – Average Velocity z/D = 1/4 z/D = 1/2

Results – Average Velocity z/D = 1 z/D = 2

Results – Velocity Deficit z/D = 1/4 z/D = 1/2

Results – Velocity Deficit z/D = 1 z/D = 2

Results – Turbulence Intensity z/D = 1/4 z/D = 1/2

Results – Turbulence Intensity z/D = 1 z/D = 2

Results – Percentage of Velocity Recovery

Results – Percentage of Velocity Recovery

Results – Hub Height Velocity Recovery

Conclusions It is known that experimental studies give point data, while CFD studies give field data. This work compromised the situation by giving semi-field data. The wake characteristics scan provided by this study clarifies the blur image and strengthen our grasp of the shear layer expansion and blade-formed vortices shedding downstream of a single wind turbine, particularly for low inflow wind speed (5 m/s) While selecting the distance between two successive wind turbines in an inline configuration wind farm, for low inflow wind speed (5 m/s), 6 rotor diameters is very short to obtain an appropriate velocity recovery, since it doesn’t exceed 65%. If the available space for wind farm is limited, it is preferred to compromise between the amount of extracted power and the distance separates two successive turbines. In this case, 80% velocity recovery can be obtained at downstream distance of 11 to 12 rotor diameters. If the available space for wind farm is not limited, it is preferred to extract the maximum power out of each turbine. In this case, 95% velocity recovery can be obtained at downstream distance of 25 rotor diameters.

Next Step Studying the effect of both different blowing wind speeds (by means of changing the fan’s drive motor frequency) and different blade profile designs (using 3D printing) on the optimum sitting conditions.