Liquid Biofuels

• Aerodynamic Design of Shelterbelts and Windbreaks:
• shelterbelt reduces downwind wind speed over a leeward distance proportional to its height ($H$).
• To prevent wind eddies from wrapping around the flanks and eroding protected fields, the minimum continuous length of a shelterbelt should be at least 24 times its height ($24 H$).
• Conclusion: 24 (Option 2).

Correct option: (2) 24

• Wind Shear in the Atmospheric Boundary Layer:
• Definition: The term wind shear describes the variation in wind speed and/or direction with height above the ground surface across the Earth's atmospheric boundary layer.
• Cause: Friction between moving air and ground surface topography, vegetation, and buildings slows surface winds, creating a steep vertical velocity gradient that increases with altitude up to hub height.
• Conclusion: Wind shear (Option 1).

Correct option: (1) Wind shear

• Wind Profile Power Law in Wind Resource Assessment:
• Hellmann's Power Law:

where:

• $v_1$ and $v_2$ are wind speeds at heights $z_1$ and $z_2$
• $\alpha$ is the wind shear exponent (typically $\approx 0.14 - 0.20$ for open rural terrain)
• Application: The power law is the standard engineering formulation used to extrapolate anemometer wind speeds measured at 10 m height up to commercial wind turbine hub heights (80–120 m).
• Conclusion: The power law (Option 3).

Correct option: (3) The power law