Aerodynamics Mcqs - Set 4

1)   Circulation is referred to as _____________

a. divergence of velocity
b. velocity field
c. flux of vorticity
d. velocity
Answer  Explanation 

ANSWER: divergence of velocity

Explanation:
Using Stoke’s theorem, the line integral of velocity field along a closed curve is equal to the surface integral of velocity field along a closed path normal to the area covered by the path. But we know that curl of velocity is called vorticity and hence, the circulation is called a flux of vorticity.


2)   Which of the following has more viscosity?

a. Water
b. Honey
c. Oil
d. Juice
Answer  Explanation 

ANSWER: Honey

Explanation:
Honey has more viscosity. Viscosity is the measure of the resistance offered by the flow to the shear or tensile stress. The relative motion between the two surfaces moving with different velocities is given by viscosity.


3)   The boundary layer is formed at the _____________

a. boundary of an object
b. surface of an object
c. at a point on an object
d. edges of an object
Answer  Explanation 

ANSWER: boundary of an object

Explanation:
The boundary layer is formed at the boundary of an object. The boundary layer divides the flow into two parts- Viscous and inviscid. The flow inside the boundary layer is highly viscous whereas, the flow outside the boundary is inviscid flow.


4)   The nature of the boundary layer depends on _____________

a. Mach number
b. Inertia force
c. Reynold’s number
d. Viscosity
Answer  Explanation 

ANSWER: Reynold’s number

Explanation:
The nature of the boundary layer depends on Reynold’s number which is the ratio of inertial force to viscous force. Depending on the value of Reynold’s number, the boundary layer may be laminar (the flow is continuous) or it may be turbulent ( the flow is discontinuous).


5)   In microscopic view, Circulation is a __________ quantity.

a. vector
b. dimension less
c. scalar
d. non-measurable
Answer  Explanation 

ANSWER: scalar

Explanation:
In a macroscopic view, circulation is a scalar quantity as it is defined as the line integral of velocity field over a closed region. In a microscopic view, circulation is a flux of vorticity, which makes it a vector quantity.


6)   The relation between pressure and velocity in an inviscid, incompressible flow is given by __________

a. p = constant
b. p + 0.5ρ*V² = constant
c. 0.5ρ*V² = 0
d. p + 0.5ρ*V² = 0
Answer  Explanation 

ANSWER: p + 0.5ρ*V² = constant

Explanation:
The relation between pressure and velocity can be given by p+0.5ρ*V² = constant which is called as Bernoulli’s equation. In the above equation, p is the pressure and V is the velocity which implies that as the pressure increases, velocity decreases and vice versa.


7)   The aircraft fly based on which principle _________

a. Newton’s third law
b. Conservation of mass
c. Bernoulli’s principle
d. Gravity
Answer  Explanation 

ANSWER: Bernoulli’s principle

Explanation:
An aircraft fly based on Bernoulli’s principle. As the air speed increases, the pressure decreases which results in high lift generation. According to this principle, the pressure is inversely proportional to velocity.


8)   Bernoulli’s equation is applicable only for _______

a. Irrotational flow
b. Viscous flow
c. Inviscid, incompressible flow
d. Compressible flow
Answer  Explanation 

ANSWER: Inviscid, incompressible flow

Explanation:
Bernoulli’s equation is applicable only for inviscid and incompressible flow because in inviscid flow, the viscosity is zero and hence no viscous forces acts on the body also incompressible flow means the density remains constant. The inviscid and incompressible flow reduces many fluid problems.


9)   The point where the fluid comes to rest is called as ___________

a. Rest point
b. Stagnation point
c. Viscous point
d. Boundary layer point
Answer  Explanation 

ANSWER: Stagnation point

Explanation:
Stagnation point is the point where the flow slows down and come to rest. The streamline divides the flow into two parts- the upper flow and the lower flow. At a point, the flow cannot enter into an object so it has to stop and that point is called a stagnation point.


10)   Stagnation pressure or the total pressure is the sum of _________

a. Kinetic and potential energy
b. Static and dynamic pressure
c. Kinetic energy +potential energy +gravity
d. Cannot be determined
Answer  Explanation 

ANSWER: Static and dynamic pressure

Explanation:
The total pressure or stagnation pressure is the sum of static and dynamic pressure. Let p0 be the total pressure, ps be the static pressure and pd be the dynamic pressure.
Therefore, p0 = ps + pd.


11)   The dynamic pressure is given by ______

a. 0.5ρ*V²
b. ρ* V²
c. 3*V²
d. 5ρ* V²
Answer  Explanation 

ANSWER: 0.5ρ*V²

Explanation:
The dynamic pressure is not actually a pressure. It simply justifies the decrease in pressure due to the increase in the velocity. It simply justifies that when the density is half and the velocity is squared, the pressure decreases.


12)   The coefficient of pressure at stagnation point is ___________

a. 0
b. 0.5
c. 1
d. 2
Answer  Explanation 

ANSWER: 1

Explanation:
The coefficient of pressure is the dimensional less quantity and it describes the relative pressure at each and every point in a flow field. At stagnation point, its value is maximum and it can change from point to point in a flow field.


13)   The pressure for an ideal gas can be given by ____________

a. pV=nRT
b. p=RT
c. pV=T
d. p=VT
Answer  Explanation 

ANSWER: pV=nRT

Explanation:
In an ideal gas, molecules does not have volume and hence they do not interact with each other. For an ideal gas, the pressure is directly proportional to temperature and is inversely proportional to volume.


14)   Bernoulli’s equation can be directly applied to viscous flow.

a. True
b. False
Answer  Explanation 

ANSWER: False

Explanation:
No, the Bernoulli’s equation cannot be directly applied to viscous flow because in viscous flow, the motion of the fluid particle is constant. Hence, we need to convert the viscous flow into Navier-stoke equation and then Bernoulli’s equation can be applied to it.


15)   Bernoulli’s equation can be applied to compressible flow at which of the following matches the number?

a. mach number less than 1
b. mach number equal to 1
c. higher mach numbers
d. does not depends on mach number
Answer  Explanation 

ANSWER: higher mach numbers

Explanation:
Bernoulli’s principle states that increasing the velocity decreases the pressure which gives us a higher lift. If the matches the number increases, gradually the pressure decreases which leads to an increase in lift.


16)   Bernoulli’s principle is derived from which of the following?

a. Conservation of mass
b. Conservation of energy
c. Newton’s law of motion
d. Conservation of momentum
Answer  Explanation 

ANSWER: Conservation of energy

Explanation:
It states that the sum of all the forms of energy in flow is the same at all the points in that flow field. The energy here refers to kinetic energy, potential energy and internal energy.


17)   An increase in the speed of the flow leads to an increase in kinetic energy and dynamic pressure.

a. True
b. False
Answer  Explanation 

ANSWER: True

Explanation:
An increase in speed of the flow leads to an increase in kinetic energy and dynamic pressure (0.5ρ*V2). As the dynamic pressure increases that is the density is halved and the velocity is squared, the static pressure decreases along with the decrease in potential energy and internal energy.


18)   The flows in which all the flow parameters are the function of ‘x’ is called as _________

a. 3D flow
b. 2D flow
c. Quasi 1D flow
d. Quasi 2D flow
Answer  Explanation 

ANSWER: Quasi 1D flow

Explanation:
Generally, the flow field properties are uniform across any cross section and hence, they vary only in x-direction. All the flow parameters are assumed to be the function of x. A=A(x), V=V(x), p=p(x) and since they vary only in one direction they are called quasi 1D flow.


19)   Incompressible flow is the one in which density is ___________

a. 0
b. constant
c. varies from point to point
d. negligible
Answer  Explanation 

ANSWER: constant

Explanation:
In incompressible flow, the density remains constant because of which the fluids cannot be compressed and are called as incompressible fluids. Water is the best example of incompressible fluids. But still some extent we can compressible water.


20)   In a wind tunnel, the section with minimum area is called as __________

a. exit
b. nozzle
c. inlet
d. throat
Answer  Explanation 

ANSWER: throat

Explanation:
When the flow enters the wind tunnel (convergent-divergent) with a velocity V1 and pressure P1. The velocity increases and the pressure decreases at the minimum area section called the throat. Pressure is minimum at the throat.