# Aerodynamics Questions and Answers – Doublet Flow

This set of Aerodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Doublet Flow”.

1. When the amount of fluid displaced is equal to weight of body, it is called as _______
a) metacentre
b) buoyancy
c) centre of buoyancy
d) centre of gravity

Explanation: When a body is submerged in a fluid, the fluid exerts upward pressure on the body. This upward force is known as buoyancy or the force of buoyancy, and it is equal to the weight of the fluid displaced by the body.

2. Which of the following is suitable for the jet of oil in an unbroken stream?
a) temperature
b) surface tension
c) capillarity
d) vapour pressure

Explanation: The surface tension of a fluid is a property that develops due to the cohesive force between the fluid’s molecules. The molecules of oil and air interact in an oil jet, and the oil molecules also aim to acquire the smallest possible area.

3. The ratio of Inertia force to elastic force is called as ________
a) Reynold’s number
b) Froude number
c) Weber number
d) Mach number

Explanation: The inertial force is given by-ρ*L2*V22 and the elastic force is given by- K*X*A.
Therefore, the mach number is given by- ρ* L2* V2/K*X*A which gives, V2/(K/ρ).

4. The sound which can be related to explosion in human ears is _____
a) high frequency sound
b) low frequency sound
c) boom
d) sonic boom

Explanation: A sonic boom is a sound that is produced by shock waves formed by an item travelling faster than the speed of sound. When an aeroplane travels at a high speed, it generates a sequence of pressure waves, which when combined result in a sonic boom.

5. When the velocity at a point becomes zero, it refers to ___________
a) slip condition
b) no slip condition
c) positive slip condition
d) negative slip condition

Explanation: The velocity at a location at the edge of a solid becomes zero. The no-slip requirement is exemplified by Dirichlet’s condition. The particle does not move when the adhesive forces are greater than the cohesive forces, and so no slip-condition arises.

6. Density is ratio of __________
a) mass to volume
b) volume to mass
c) mass to pressure
d) pressure to volume

Explanation: The density of a substance is measured in kilogrammes per metre cube and is expressed as a ratio of mass to volume. The density of liquids remains constant as pressure and temperature fluctuate, whereas the density of gases changes.

7. The units of viscosity are __________
a) N/m
b) Ns/m2
c) m/s
d) Dimension less quantity

Explanation: The viscosity of a fluid is defined as the property of the fluid that resists the movement of one layer over another. It is shear stress that is required to produce a unit rate of shear strain, which is equal to force*time/length2, or Ns/m2.

8. When velocity potential (Φ) is constant, it is called as _________
a) velocity line
b) velocity curve
c) potential line
d) equipotential line

Explanation: The line along which the velocity potential (Φ) is constant is called a equipotential line. For an equipotential line,
Φ=constant and also dΦ=0
The slope for the equipotential line can be given as=dy/dx.

9. Series of equipotential lines and streamlines is ________
a) flow net
b) constant flow
c) equilibrium flow
d) positive flow

Explanation:A flow net is a grid created by drawing a succession of equipotential lines and stream lines. In the analysis of two-dimensional flow issues, a flow net is a useful tool.

10. When both the source and sink are of equal strength it is called ________
a) sink
b) source
c) doublet
d) positive derivative of flow

Explanation: The specific case of a source and sink with identical strength is known as a doublet. Let q and -q represent the source and sink strength, respectively. Allow 2a to represent the distance between the source and the sink, which approaches zero. Doublet strength refers to the product 2a*q.

We see that a doublet is generated when the source and sink approach each other at the same moment, i.e., at the same angle. (86.4) As a result, the stream function changes. Doublet. By superimposing the velocity potential and stream functions of the above-mentioned simple flows, we may now create other flow patterns. Imagine a source and a sink of equal power K at equal distances s from the origin along the x-axis to generate a doublet, as shown in Fig. 21.4. The radial velocity tends to be infinite as the doublet’s centre is approached. It demonstrates that the doublet flow is solitary. The obvious inference from Eq. 21.20 is that doublet flow is an irrotational flow.