Correct Answer

Concept & PrincipleElectricalPower Generation

Option C

Lift & drag

Quick Summary: Wind turbine blades operate based on the principles of aerodynamics, specifically the generation of lift and drag forces due to the airflow over an airfoil profile. The resultant of these forces creates the torque necessary to rotate the turbine hub and generate electricity.

💡 Explanation

Wind turbine blades operate based on the principles of aerodynamics, specifically the generation of lift and drag forces due to the airflow over an airfoil profile. The resultant of these forces creates the torque necessary to rotate the turbine hub and generate electricity.

🔢 Key Formulas

$F_L = \frac{1}{2} \rho A v^2 C_L$ — Lift force acting perpendicular to the relative wind

$F_D = \frac{1}{2} \rho A v^2 C_D$ — Drag force acting parallel to the relative wind

⚙️ Working Principle

As wind flows over the curved surface of a blade, a pressure difference is established between the upper and lower surfaces (Bernoulli's principle), resulting in a lift force perpendicular to the wind direction. Simultaneously, friction and pressure imbalances cause a drag force parallel to the wind direction. The vector sum of these forces provides the driving force for the turbine, where $F_{lift} = \frac{1}{2} \rho A v^2 C_L$ and $F_{drag} = \frac{1}{2} \rho A v^2 C_D$ .

📌 Key Points

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Lift force is primarily responsible for the rotational torque of the turbine.
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Drag force opposes the motion and can cause losses, though it is used in some specialized designs.
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The airfoil shape is optimized to maximize the Lift-to-Drag ratio ( $C_L/C_D$ ).
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Wind turbines are essentially energy converters that transform kinetic wind energy into mechanical energy via these aerodynamic forces.

✅ Advantages

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High conversion efficiency at optimal wind speeds.
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Well-understood aerodynamic principles allowing for precise blade design.

❌ Disadvantages / Limitations

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Subject to mechanical stress and fatigue due to force fluctuations.
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High sensitivity to wind turbulence and gusting conditions.

🛠️ Applications / Uses

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Horizontal Axis Wind Turbines (HAWT)
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Vertical Axis Wind Turbines (VAWT)

📄 Additional Information

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$\rho$ represents air density (approx $1.225 kg/m^3$ at sea level).
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Option A (Viscous force) is a component of drag, but incomplete. Option B (Inertia force) relates to the structural mass during start-up or gust conditions, but is not the primary force for power generation.

📊 Diagram / Illustration

✅

C is correct — Lift and drag are the two primary aerodynamic forces generated by the interaction between the wind and the turbine blade profile.

Core Concepts Used

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Aerodynamics of airfoils Bernoulli's Principle Wind kinetic energy extraction

💡 EXAM TIP

Remember that in turbine design, the Angle of Attack determines the ratio of Lift to Drag; managing this is critical for maximizing power coefficient ( $C_p$ ).

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