This set of Aerodynamics Questions and Answers for Freshers focuses on “Angular Velocity, Vorticity, Strain”.

1. The rate of change of angular position of the body is called as _________

a) Angular displacement

b) Angular velocity

c) Angular acceleration

d) Distance

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Explanation: Angular velocity comes in the picture when the flow is rotational that is the flow which has both translational as well as rotational motion. It is the rate of change of angular displacement. It is denoted by omega and its SI unit id radian per second.

2. When an element moves in a flow field it translates, it also rotates along a streamline and in addition, its shape may undergo distortion.

a) True

b) False

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Explanation: An element may undergo distortion because when a body translates n rotate some of its parts me undergo external forces because of the shape of the element may change. The amount of distortion depends on the velocity field.

3. The angular velocity can be given by ______________

a) ω = 0.5(dθ_{1}/dt + dθ_{2}/dt)

b) ω = (dθ_{1}/dt + dθ_{2}/dt)

c) ω = 4(dθ_{1}/dt + dθ_{2}/dt)

d) ω = 8(dθ_{1}/dt + dθ_{2}/dt)

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Explanation: Angular velocity is defined as the average of the angular velocities of the lines (2D or 3D). This is the case of 2D flow. Consider a flow, let dθ

_{1}/dt be the x component of velocity and dθ

_{2}/dt be the y component of velocity.

4. The term 2*ω is called as _____________

a) Velocity

b) Divergence

c) Angular velocity

d) Vorticity

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Explanation: Vorticity is twice the angular velocity. The angular velocity of the fluid plays an important role in theoretical aerodynamics and 2*ω occurs frequently and in order to reduce the complexity, we use vorticity.

5. The curl of velocity equals to _______

a) velocity

b) pressure

c) vorticity

d) angular velocity

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Explanation: The curl of velocity and the vorticity for a 3D flow is the same. Therefore, the curl of velocity equals to the vorticity of the 3D flow element. The equation can be defined by 2*ω = ∇*V where ∇*V – curl of velocity and 2*ω is the vorticity.

6. If ∇*V is not equal to zero, then the flow is __________

a) steady

b) unsteady

c) rotational

d) irrotational

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Explanation: In rotational flow, the fluid element has a finite angular velocity which means the element can undergo rotation and as well as distortion. The amount of distortion depends on the velocity field.

7. If ∇*V is equal to zero, then the flow is _________

a) steady

b) unsteady

c) rotational

d) irrotational

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Explanation: In irrotational flow, the fluid element does not have a finite angular velocity which means the element cannot undergo rotation and as well as distortion. The motion of the fluid element is purely translational motion.

8. The subsonic flow over an airfoil is an example of __________

a) steady

b) unsteady

c) rotational

d) irrotational

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Explanation: For the subsonic flow over an airfoil, the flow is irrotational which means the motion of the fluid element is translational. In such cases, a thin boundary layer is formed around the surface. In this boundary layer, the flow is highly rotational whereas, outside the boundary layer it is irrotational.

9. The angle between the two lines (x and y direction) is called as ___________

a) viscous layer

b) strain

c) stress

d) velocity vector

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Explanation: Strain is defined as the change in angle between the two lines in a flow field. Suppose Δθ

_{1}and Δθ

_{2}are the angles between the two lines in a flow field. Therefore, strain can be given by – Strain= Δθ

_{2}– Δθ

_{1}.

10. The absence of vorticity means the flow is ________

a) steady

b) unsteady

c) rotational

d) irrotational

View Answer

Explanation: The absence of vorticity means the flow is irrotational flow, which simplifies the flow analysis. This is greatly used in case of inviscid flows. The flow analysis becomes easy for irrotational flow since there is no rotational motion of the fluid element.

**Sanfoundry Global Education & Learning Series – Aerodynamics.**

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