# Aerodynamics Questions and Answers – The Kutta-Joukowski Theorem

This set of Aerodynamics Multiple Choice Questions & Answers (MCQs) focuses on “The Kutta-Joukowski Theorem”.

**1. Define Kutta-Joukowski theorem.**

**a) Lift per unit span on the airfoil**

b) Drag per unit span on the airfoil

c) Moment per unit span on the airfoil

d) Thrust per unit span on the airfoil

**Explanation**: According to the Kutta-Joukowski theorem, lift per unit span on a two-dimensional body is proportional to circulation across the body. It is an aerodynamics fundamental theorem that is used to calculate the lift of an airfoil and any two-dimensional body.

**2. What is the angle of attack of lift producing airfoil?**

a) Angle of attack less than zero

**b) Angle of attack greater than zero**

c) Angle of attack is zero

d) Angle of attack remains the same

**Explanation**: A lift-producing airfoil has camber or is translating in a uniform fluid at a larger than zero angle of attack. It must also have a sharp trailing edge. When air passes over an airfoil, it exerts a downward pull on the air.

**3. How the fluid moves on the airfoil?**

a) Lower surface

b) Upper and middle surface

c) Upper surface

**d) Lower and upper surface**

**Explanation:** The sharp trailing edge should meet fluid travelling along the lower and upper surfaces of the airfoil. The fluid cannot turn around the sharp edge due to viscous dissipation. For genuine flow, this is known as the Kutta-Condition.

**4. What is the condition for Kutta and Joukowski theorem?**

**a) Pressure and lift**

b) Pressure and drag

c) Drag and lift

d) Lift and moment

**Explanation**: Kutta and Joukowski demonstrated that if the Kutta condition is imposed, the pressure and lift of a thin enough airfoil in a flow with a big enough Reynolds number and a short enough angle of attach can be assumed inviscid in the entire region.

**5. What is the flow outside the airfoil?**

**a) Irrotational**

b) Rotational

c) Circumferential

d) Constant

**Explanation**: Because the flow outside the airfoil is irrotational, circulation around any closed curve that does not enclose the airfoil is zero. When the boundary layer separates, the displacement thickness of the outer potential flow and pressure field changes dramatically.

**6. How rotating flow is induced?**

a) Joint effect of airfoil

b) Joint effect of chord

**c) Joint effect of camber**

d) Joint effect of camber line

**Explanation**: The combined effects of camber, angle of attack, and the sharp trailing edge of the airfoil produce rotating flow, which should not be mistaken with a tornado-like vortex encircling the cylinder or wing of an aeroplane in flight.

**7. Kutta-Joukowski theorem refers to __________**

**a) two-dimensional flow around an airfoil**

b) one-dimensional flow around an airfoil

c) three-dimensional flow around an airfoil

d) flows around an airfoil

**Explanation:** The Kutta-Joukowski theorem determines the lift generated by one unit of a span in two-dimensional flow around an airfoil. Although the Kutta-Joukowski theorem is an opaque theory, it is a decent approximation for real viscous flow in most aeronautical applications.

**8. What is the condition for rotational flow in Kutta-Joukowski theorem?**

a) Small number of unsteady flow

**b) Large number of unsteady flow**

c) Large number of steady flow

d) Small number of steady flow

**Explanation**: The flow is rotational when there are free vortices outside of the body, as there may be in a large number of unstable flows. If fluid particles rotate around their own mass centre, the fluid is said to be rotational; otherwise, the flow is said to be irrotational.

**9. Is Kutta-Joukowski theorem is fundamental theorem of aerodynamics?**

**a) True**

b) False

**Explanation**: The Kutta-Joukowski theorem is a fundamental theorem of aerodynamics that may be used to calculate the lift of an airfoil or any two-dimensional body, such as circular cylinders, moving in a uniform fluid at a constant speed big enough to keep the flow visible in the body steady and unseparated.

**10. Is Kutta-Joukowski theorem relate to lift?**

a) False

**b) True**

**Explanation**: The Kutta-Joukowski theorem is a relationship between the lift created by an airfoil and its speed. The fluid, the density of the fluid, and the circulation are all influenced by the fluid. This theorem connects lift and circulation in the same way as the Magnus effect connects side force and rotation.

**11. Define circulation.**

**a) Line integral around a closed loop enclosing the airfoil**

b) Line integral around an open loop enclosing the airfoil

c) Line integral around an in loop enclosing the airfoil

d) Line integral of airfoil

**Explanation**: The line integral around a closed loop enclosing the airfoil of the component of the fluid velocity tangent to the loop is defined as circulation. To compute the force on an airfoil, the vorticity outside the boundary layer is zero, and the circulation through each circuit is the same.

The Kutta–Joukowski theorem is a fundamental theorem in aerodynamics that is used to calculate the lift of an airfoil and any two-dimensional bodies, such as circular cylinders, moving in a uniform fluid at a constant speed large enough to keep the flow steady and unseparated in the body-fixed frame. According to the Kutta-Joukowski theorem, lift per unit span on a two-dimensional body is proportional to circulation across the body. It is an aerodynamics fundamental theorem that is used to calculate the lift of an airfoil and any two-dimensional body.