# Angular Velocity, Vorticity, Strain Questions and Answers

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

1. The term 2*ω is called as _____________
a) Velocity
b) Divergence
c) Angular velocity
d) Vorticity

Explanation: The vorticity is equal to the angular velocity multiplied by two. In theoretical aerodynamics, the fluid’s rotational velocity is significant, because 2* happens frequently, thus we employ vorticity to simplify the complexity.

2. The curl of velocity equals to _______
a) velocity
b) pressure
c) vorticity
d) angular velocity

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.

3. If ∇*V is not equal to zero, then the flow is __________
c) rotational
d) irrotational

Explanation: The fluid element in rotational flow has a finite angular velocity, which means the element can rotate as well as deform. The magnitude of the distortion is determined by the velocity field.

4. If ∇*V is equal to zero, then the flow is _________
c) rotational
d) irrotational

Explanation: The fluid element in irrotational flow does not have a limited angular velocity, hence it cannot rotate or deform. The fluid element moves in a purely translational way.

5. The subsonic flow over an airfoil is an example of __________
c) rotational
d) irrotational

Explanation: The flow is irrotational for subsonic flow over an airfoil, which means the fluid element’s motion is translational. A thin boundary layer forms surrounding the surface in such instances. The flow in this boundary layer is strongly rotating, whereas it is irrotational outside of it.

6. The angle between the two lines (x and y direction) is called as ___________
a) viscous layer
b) strain
c) stress
d) velocity vector

Explanation: Strain is defined as the change in angle between the two lines in a flow field. Suppose Δθ1 and Δθ2 are the angles between the two lines in a flow field. Therefore, strain can be given by – Strain= Δθ2 – Δθ1.

7. The absence of vorticity means the flow is ________
c) rotational
d) irrotational

Explanation: Irrotational flow is defined by the absence of vorticity, which simplifies flow analysis. In the case of inviscid flows, this is extremely useful. Because there is no rotating motion of the fluid element, flow analysis becomes simple for irrotational flow.

8. The rate of change of angular position of the body is called as _________
a) Angular displacement
b) Angular velocity
c) Angular acceleration
d) Distance

Explanation: When a flow is rotational, that is, when it contains both translational and rotational motion, angular velocity enters the picture. It is the rate at which angular displacement changes. The symbol for it is omega, and the SI unit is radian per second.

9. 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

Explanation: When a body translates and rotates, certain of its portions may be subjected to external forces, causing the element’s shape to alter. The magnitude of the distortion is determined by the velocity field.

10. The angular velocity can be given by ______________
a) ω = 0.5(dθ1/dt + dθ2/dt)
b) ω = (dθ1/dt + dθ2/dt)
c) ω = 4(dθ1/dt + dθ2/dt)
d) ω = 8(dθ1/dt + dθ2/dt)

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 dθ1/dt be the x component of velocity and dθ2/dt be the y component of velocity.