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Aerodynamics - Inviscid & Incompressible Flow Quiz(MCQ)
1 .
The aircraft fly based on which principle ______
A)
Gravity
B)
Bernoulli’s principle
C)
Newton’s third law
D)
Conservation of mass

Correct 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.

2 .
Bernoulli's equation is applicable only for _______
A)
Viscous flow
B)
Irrotational flow
C)
Compressible flow
D)
Inviscid, incompressible flow

Correct 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.

3 .
The point where the fluid comes to rest is called as __________
A)
Rest point
B)
Viscous point
C)
Stagnation point
D)
Boundary layer point

Correct 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.

4 .
Stagnation pressure or the total pressure is the sum of _________
A)
Static and dynamic pressure
B)
Kinetic and potential energy
C)
Kinetic energy +potential energy +gravity
D)
None of the above

Correct 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.

5 .
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

Correct 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.

6 .
Bernoulli's equation can be applied to compressible flow at which of the following matches the number?
A)
higher mach numbers
B)
mach number equal to 1
C)
mach number less than 1
D)
does not depends on mach number

Correct 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.

7 .
The pressure for an ideal gas can be given by __________
A)
p=RT
B)
pV=T
C)
p=VT
D)
pV=nRT

Correct 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.

8 .
The flows in which all the flow parameters are the function of ‘x’ is called as ________
A)
Quasi 1D flow
B)
Quasi 2D flow
C)
3D flow
D)
None of the above

Correct 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.

9 .
Incompressible flow is the one in which density is _________
A)
negligible
B)
constant
C)
varies from point to point
D)
None of the above

Correct 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.

10 .
In a wind tunnel, the section with minimum area is called as ________
A)
exit
B)
inlet
C)
throat
D)
nozzle

Correct 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.

11 .
The below figure shows which of the following wind tunnel?
A)
Simple duct
B)
Divergent duct
C)
Convergent duct
D)
Convergent-divergent duct

Correct Answer :   Convergent-divergent duct

Explaination : The velocity increases in the convergent duct (V1) and the reaches V2 at the throat and the pressure becomes minimum at the throat condition. In the divergent section, the velocity decreases and the pressure begin to increases.

12 .
Inside a wind tunnel, the area further decreases from A2 to A3, that section is called as _______
A)
Nozzle
B)
Divergent section
C)
Throat section
D)
Converging section

Correct Answer :   Divergent section

Explanation : The purpose of the diffuser is to reduce the velocity. In order to decrease the velocity, the wind tunnel is designed in such a way that the area in the divergent section decreases and the pressure in this section increases further.

13 .
Which of the following is an application of incompressible flow in a duct?
A)
Low speed wind tunnel
B)
Flow in air
C)
Cannot be said
D)
High speed wind tunnel

Correct Answer :   Low speed wind tunnel

Explanation : Low speed wind tunnel is a large venturi where the airfoil is driven by a fan connected to some type of motor drive. The wind tunnel fan is similar to the propeller of an aircraft and is designed to draw the airflow through the tunnel circuit.

14 .
The carburetor of an automobile engine makes use of _____
A)
wind tunnel
B)
venturi duct
C)
divergent duct
D)
convergent duct

Correct Answer :   venturi duct

Explanation : In venturi duct, the pressure at the throat(p2) is lower than the pressure at the inlet(p1). The pressure difference p2-p1 helps to force the fuel into the airstream and mix it with the airstream downstream of the throat.

15 .
Which of the following parameter can be measured using venturi?
A)
volume
B)
density
C)
velocity
D)
temperature

Correct Answer :   temperature

Explanation : Using venturi, velocity can be measured. We can calculate the pressure difference using venturi. In the duct, we can place pressure gauge which will directly give us the pressure difference (p2-p1). This pressure difference can be related to velocity using Bernoulli’s equation and hence, the velocity can be calculated.

16 .
The randomness of the molecules gives us ________ pressure.
A)
Static
B)
Dynamic
C)
Absolute
D)
Stagnation

Correct Answer :   Static

Explanation : Static pressure is the measure of purely random motion of the molecules of the gas. It is the pressure which we can feel when we ride along with the gas at the local flow velocity. For reference, we always consider pressure as static pressure.

17 .
How does the pitot tube help in measuring the airspeed?
A)
Using velocity
B)
Using temperature
C)
Using mach number
D)
Using the pressure difference

Correct Answer :   Using the pressure difference

Explanation : The pitot tube is closed at one end and is opened from other ends. When the air is filled inside the tube, the pressure at the open end equals to total pressure and it differs from the pressure outside the tube. Using this pressure difference and applying Bernoulli’s equation, the speed of air can be calculated.

18 .
The instrument which combines both the static and total pressure is _______
A)
Static probe
B)
Dynamic probe
C)
Pitot static probe
D)
Stagnation probe

Correct Answer :   Pitot static probe

Explanation : A pitot static probe is to combine the measurement of static and total pressure. It measures p0 at the nose of the probe and p1 at a suitably placed static pressure tap on the probe surface downstream of the nose.

19 .
The dynamic pressure can be given by __________
A)
sum of total and static pressure
B)
difference of total and static pressure
C)
double of total and static pressure
D)
product of total and static pressure

Correct Answer :   difference of total and static pressure

Explanation : In incompressible flow, the dynamic pressure has a special meaning, it is a difference between the total pressure and the static pressure. Let p0 be the total pressure and p1 be the static pressure.
Therefore, the dynamic pressure (q)= total pressure (p0)- static pressure (p1).

20 .
The pressure measured relative to vacuum is ______
A)
total pressure
B)
absolute pressure
C)
static pressure
D)
dynamic pressure

Correct Answer :   absolute pressure

Explanation : Absolute pressure is measured with respect to vacuum. A vacuum has an absolute pressure of 0 psi. It is also defined as the sum of gauge pressure and atmospheric pressure.

21 .
The errors generated in the pitot tube due to the location are called __________
A)
position errors
B)
normal errors
C)
positive errors
D)
negligible errors

Correct Answer :   position errors

Explanation : The errors that occur due to the location of pitot tube on an aircraft and also due to the effect of localized airflow over the pitot tube are called as position errors. These errors are needed to be considered while calculations.

22 .
The lower end of the pitot tube is bet at an angle of __________
A)
45 degrees
B)
90 degrees
C)
120 degrees
D)
360 degrees

Correct Answer :   90 degrees

Explanation : The lower end of the tube is bent at an angle of 90 degrees. The liquid rises up in the tube due to the conversion of kinetic energy into the pressure energy. The velocity is determined by measuring the rise of the liquid in the tube.

23 .
In a pitot tube, the kinetic energy is converted into ______
A)
total energy
B)
internal energy
C)
pressure energy
D)
potential energy

Correct Answer :   pressure energy

Explanation : When the velocity of the flow becomes zero, the pressure is increased due to the conversion of kinetic energy into pressure energy which leads to the generation of the pressure difference.

24 .
Coefficient of pressure is a ________
A)
negligible value
B)
dimensional quantity
C)
cannot be determined
D)
dimensionless quantity

Correct Answer :   dimensionless quantity

Explanation : Although pressure is dimensional quantity, Coefficient of pressure is dimension less quantity. It is used throughout the aerodynamics from incompressible flow to hypersonic flow. In aerodynamics, it is very easy to find coefficient of pressure rather than pressure.

25 .
The highest value of Cp is given at ________
A)
end points
B)
at boundaries
C)
stagnation point
D)
everywhere in the flow field

Correct Answer :   stagnation point

Explaination : At stagnation point, the value of velocity is 1 and therefore Cp = 1 – (V2/ V1)2
Gives the value of the coefficient of pressure as 1. This is true only for incompressible flow. Stagnation point gives the highest value of the coefficient of pressure.

26 .
For incompressible flow, Cp is expressed only in terms of ___________
A)
velocity
B)
density
C)
pressure
D)
temperature

Correct Answer :   velocity

Explaination : In incompressible flow, the pressure and velocity at two different points can be given by-
P1+0.5*ρ*V12 = P2+0.5*ρ*V22
From here we get, P2-P1 = 0.5*ρ (V12– V22)
Hence, Cp = (P2-P1)/q
Where q-dynamic pressure
On solving the above equation we get, Cp = 1 – (V2/ V1)2.

27 .
The most common device used for measuring air speed is ________
A)
altimeter
B)
thermometer
C)
pitot tube
D)
pressure gauge

Correct Answer :   pitot tube

Explanation : Pitot tube is a tube bent in L shaped. The one end of the pitot tube is exposed to air so that it can directly come in contact with the flow velocity. The pressure inside this tube is used to measure the velocity.

28 .
Which of the following is an example of hydrostatic manometer?
A)
pressure gauge
B)
piston type gauge
C)
spring manometer
D)
mercury column manometer

Correct Answer :   mercury column manometer

Explanation : This type of manometers are used to measure the pressure as well as compare it with the hydrostatic force per unit area at the base of the column. They have a poor dynamic response.

29 .
The shape of the wing is called as ________
A)
wing
B)
airfoil
C)
geometry
D)
wing box

Correct Answer :   airfoil

Explanation : The shape of the wing is called airfoil. When the flow passes over an airfoil, it produces aerodynamic forces. Instead of analyzing the complete wing, the analysis is done on an airfoil which gives similar characteristics like a wing.

30 .
The pressure and temperature are ________
A)
directly proportional to each other
B)
independent of each other
C)
inversely proportional to each other
D)
None of the above

Correct Answer :   directly proportional to each other

Explanation : Gay-Lussac’s law states the relationship between temperature and pressure. They are directly proportional to each other. Increase in temperature increases the pressure and vice versa. When the temperature increases, the gas molecules move faster and hence the pressure increases.

31 .
Pressure is _____ proportional to altitude.
A)
equal
B)
directly
C)
inversely
D)
no relation

Correct Answer :   inversely

Explanation : Pressure is inversely proportional to altitude. As altitude increases, pressure decreases and vice versa because the air molecules are pulled downwards due to the gravitational force of the earth and hence, all the molecules are close at lower altitude thus generating higher pressure at lower altitudes.

32 .
Cl vs Cd is called as _________
A)
drag polar
B)
total drag
C)
parasitic drag
D)
no significance

Correct Answer :   drag polar

Explanation : It is called drag polar and it gives the relation between the lift and drag of the aircraft. It describes the amount of lift generated per drag produced. Cl/Cd ratio must be high. The amount of lift generated should be more with relatively less drag.

33 .
The flow in which the parameters do not change with respect to time is called as ________
A)
unsteady flow
B)
transient flow
C)
continuous flow
D)
steady uniform flow

Correct Answer :   steady uniform flow

Explanation : The flow in which the flow parameters do not change with respect to time is called a steady uniform flow. The steadiness and uniformity need not occur together. The flow particles move in a line with constant velocity.

34 .
The flow in which the flow parameters change from one point to other is called _________
A)
steady flow
B)
linear flow
C)
non-uniform flow
D)
uniform flow

Correct Answer :   non-uniform flow

Explanation : The flow in which all the hydrostatic parameters change from one point to other is called non-uniform flow. The changes may be in direction of flow or in the direction perpendicular to the flow. The example of the changes perpendicular to the flow is the flow over the solid bodies.

35 .
The tapering pipe is an example of ______
A)
steady uniform flow
B)
steady non-uniform flow
C)
unsteady uniform flow
D)
unsteady non-uniform flow

Correct Answer :   steady non-uniform flow

Explanation : The flow in a tapering pipe has variable geometry. The cross section of the tapered pipe is not uniform but the rate of fluid flow is constant throughout the flow. Any duct which has non-uniform cross section but the hydrostatic parameters remain constant fall under this category.

36 .
Two pathline can ________
A)
cannot meet ever
B)
intersect each other
C)
can meet at infinity
D)
cannot intersect each other

Correct Answer :   intersect each other

Explanation : Two pathlines can intersect each other because the same particle or the different particle may come again at the same place at different time. Moreover, pathline is just a path followed by the fluid particle. Two or more fluid particles can follow the same path.

37 .
In steady flow, pathline and stream lines are _______
A)
same
B)
different
C)
slightly similar
D)
None of the above

Correct Answer :   same

Explanation : A pathline is a path followed by a fluid flow particle. Whereas, streamline is a point in the fluid flow at which if a tangent is drawn, it gives the direction of the fluid flow. But in a steady flow, the velocity remains constant throughout the flow, hence the pathline and streamline become the same.

38 .
The flow in which streamlines are directed away from the origin is called as ________
A)
sink flow
B)
doublet flow
C)
source-sink flow
D)
source flow

Correct Answer :   source flow

Explanation : In a source flow, the flow velocity is directed away from the origin. All the streamlines are the straight lines and they vary inversely with distance which means as the distance increases the velocity decreases.

39 .
The opposite case of the source flow is ________
A)
sink flow
B)
doublet flow
C)
source flow
D)
source-sink flow

Correct Answer :   sink flow

Explanation : The flow in which the streamlines are directed towards the origin is called as sink flow. The sink flow is simply the negative of source flow. The streamlines vary inversely with the distance that is as the distance decreases the velocity increases.

40 .
The origin is called as ________
A)
sink point
B)
singular point
C)
source point
D)
multiple point

Correct Answer :   singular point

Explanation : For a source flow, divergence of velocity is zero everywhere expect at the origin where it is infinite. Thus, the origin is a singular point and we can interpret this singular point as a discrete source or sink of a given strength, with a corresponding induced flow field about the point.

41 .
________ is the scalar function of the space and time.
A)
velocity
B)
pressure
C)
velocity vector
D)
velocity potential function

Correct Answer :   velocity potential function

Explanation : Velocity function is the scalar function of space and time such that its negative derivative with respect to any direction gives the fluid velocity in that direction. It is defined by phi (?). Mathematically, it is given by, ?= f(x,y,z).

42 .
When velocity potential (?) exits, the flow is ______
A)
laminar
B)
turbulent
C)
irrotational
D)
rotational

Correct Answer :   irrotational

Explaination : When the rotational components are zero, it means that the flow travels in a linear direction and the velocity potential gives the direction of fluid velocity in a particular direction. In irrotational flow, the velocity of the fluid travels in a linear direction.

43 .
Consider a fixed point in a flow. The locus of all the point passed through this fixed point is called as _________
A)
streak lines
B)
stream-line
C)
stream tubes
D)
None of the above

Correct Answer :   streak lines

Explanation : The locus of all the points that have passed through a fixed point is called a streak line. The flow will pass through a fixed point to any other point at any instant. The locus of these points is streamline.

44 .
______ gives the velocity component at right angles to a particular direction.
A)
stream function
B)
velocity
C)
pressure line
D)
velocity vector

Correct Answer :   stream function

Explanation : Stream function is defined as the scalar function of space and time such that its partial derivative with respect to any direction gives the velocity component at right angles to that direction. It is valid only for 2D flow and is denoted by Ψ.

45 .
Stream function is defined for ____________
A)
1D flow
B)
2D flow
C)
3D flow
D)
multi-dimensional flow

Correct Answer :   2D flow

Explanation : Stream function are applicable only for 2D flow. It is denoted by psi (Ψ). For a steady state flow, it is given by- Ψ=f(x,y), such that
δΨ/δx=v and δΨ/δy=u.

46 .
When velocity potential (Φ) is constant, it is called as _____
A)
velocity line
B)
velocity curve
C)
potential line
D)
equipotential line

Correct Answer :   equipotential line

Explaination : 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.

47 .
Series of equipotential lines and streamlines is ________
A)
constant flow
B)
flow net
C)
positive flow
D)
equilibrium flow

Correct Answer :   flow net

Explanation : The grid obtained by drawing a series of equipotential lines and stream lines is called a flow net. A flow net is an important tool in analyzing two-dimensional flow problems.

48 .
When both the source and sink are of equal strength it is called ________
A)
sink
B)
source
C)
doublet
D)
positive derivative of flow

Correct Answer :   doublet

Explanation : Doublet is the special case of source and sink with equal strength. Let q and -q be the strength of source and sink respectively. Let 2a be the distance between the source and sink and it approaches zero. The product 2a*q is called as doublet strength.

49 .
Density is ratio of __________
A)
mass to volume
B)
volume to mass
C)
mass to pressure
D)
pressure to volume

Correct Answer :   mass to volume

Explanation : Density is the ratio of mass to volume and is measured in kilograms per meters cube. The density of the liquids remains constant while the density of gases changes with the variation of pressure and temperature.

50 .
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

Correct Answer :   no slip condition

Explanation : At the boundary of solids, the velocity at a point becomes zero. Dirichlet’s condition is an example of no slip-condition. When the adhesive forces are stronger than cohesive force the particle does not move and hence no slip-condition occurs.

51 .
The sound which can be related to explosion in human ears is _____
A)
boom
B)
high frequency sound
C)
low frequency sound
D)
sonic boom

Correct Answer :   sonic boom

Explanation : The sound which is related to shock waves that are created by the object travelling faster than the speed of sound is called a sonic boom. When an aircraft travels with a high speed, series of pressure waves are also created and these when combine together leads to sonic boom.

52 .
When the amount of fluid displaced is equal to weight of body, it is called as _______
A)
buoyancy
B)
metacentre
C)
centre of gravity
D)
centre of buoyancy

Correct Answer :   buoyancy

Explanation : When a body is immersed in a fluid, an upward fluid is exerted by the fluid on the body. This upward force is equal to the weight of the fluid displaced by the body and is called as buoyancy or the force of buoyancy.

53 .
Which of the following is suitable for the jet of oil in an unbroken stream?
A)
capillarity
B)
temperature
C)
surface tension
D)
vapour pressure

Correct Answer :   surface tension

Explanation : The surface tension is the property of a fluid which occurs because of the cohesive force between the molecules of the fluid. In a jet of oil, the molecules of oil and the air interact and also the molecules of the oil try to acquire the minimum area.

54 .
The ratio of Inertia force to elastic force is called as _____
A)
Weber number
B)
Froude number
C)
Mach number
D)
Reynold’s number

Correct Answer :   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).

55 .
A combination of uniform flow and doublet flow gives _______
A)
flow past a plate
B)
flow past a wedge
C)
flow over any body
D)
flow past a circular cylinder

Correct Answer :   flow past a circular cylinder

Explanation :
In the above figure, the first diagram shows the uniform flow whereas, the second one shows the doublet flow (source sink combination of equal strength). The combination of these two leads to the flow past a cylinder.

56 .
The stream function can be obtained by _______
A)
sum of stream function of uniform flow and sink flow
B)
sum of stream function of uniform flow and doublet flow
C)
sum of stream function of uniform flow and source flow
D)
difference of stream function of uniform flow and doublet flow

Correct Answer :   sum of stream function of uniform flow and doublet flow

Explanation : The stream for the resultant flow can be given by the sum of stream function of uniform flow and doublet flow. Here we need to consider cylindrical coordinates. Mathematically,
Ψ = U*y + ((-u/2*pi*r)*sin θ.

57 .
The flow past cylinder is also called as ________
A)
Vortex flow
B)
Source flow
C)
Newton's ring
D)
Rankine oval of equal axes

Correct Answer :   Rankine oval of equal axes

Explanation : The flow past cylinder is called a Rankine oval of equal axes as it was discovered by Rankine and also the flow parameters on the upper and lower surface of the doublet flow remains the same.

58 .
What will be the shape of Rankine oval when sin θ=0?
A)
horizontal line
B)
curve
C)
a point
D)
vertical line

Correct Answer :   horizontal line

Explaination : The shape of the Rankine oval of equal axes can be given by substituting the stream function as zero in the equation Ψ = U*y + ((-u/2*pi*r)*sin θ. When sin θ=0, θ=0, then a horizontal line through the origin of the doublet is formed and it is x-axis.

59 .
The amount of lift generated in the flow over a cylinder is _________
A)
No lift
B)
Infinity
C)
Positive lift
D)
Negative lift

Correct Answer :   No lift

Explanation : The pressure distribution over the top of the cylinder is exactly balanced the lower of the cylinder and also, the pressure distribution over the front of the cylinder is balanced by the pressure over the back of the cylinder and hence no lift is generated.

60 .
What will be the shape of Rankine oval when U*y+ ((-u/2*pi*r) = 0?
A)
point
B)
open curve
C)
straight line
D)
closed body profile

Correct Answer :   closed body profile

Explaination : The shape of the Rankine oval of equal axes can be given by substituting the stream function as zero in the equation Ψ = U*y + ((-u/2*pi*r)*sin θ. When U*y+ ((-u/2*pi*r) =0, a closed profile body is a circular cylinder of radius R with the centre on the doublet.

61 .
The free vortex flow forms _______
A)
parabola
B)
hyperbola
C)
concentric circles
D)
straight lines

Correct Answer :   concentric circles

Explanation : The free vortex flow is a circulatory flow of the fluid such that its stream lines are concentric circles. The velocity components for a free vortex flow are Ur and Uθ and is equal to Ur=0 and Uθ=circulation/ 2*pi*r.

62 .
The following figure is an example of _______
A)
doublet
B)
free vortex flow
C)
sink flow
D)
source flow

Correct Answer :   free vortex flow

Explaination : The above figure shows the concentric circles along with streamlines. Here, the stream function is a function of radius and it is constant value and hence the streamlines are concentric.

63 .
The combination of uniform flow and source flow gives _______
A)
flow past a cylinder
B)
flow past a half body
C)
flow past a wedge
D)
flow past a full body

Correct Answer :   flow past a half body

Explanation : When a uniform of velocity U combines with a source flow of strength q, the resultant flow is a flow over a half body.

64 .
A body floats on the surface when _______
A)
metacenter is above gravity
B)
metacenter is below gravity
C)
gravity is above metacenter
D)
metacenter is equal to gravity

Correct Answer :   metacenter is above gravity

Explanation : In case of a floating object, the metacenter should always be above gravity. Metacentre is the point about which a body starts oscillating when the body is tilted by a small angle. In the case of a floating body, the weight of an object is equal to the amount of fluid displaced.

65 .
Centre of pressure can be calculated using ________
A)
Principle of energy
B)
Mass conservation
C)
Rayleigh’s principle
D)
Principle of moments

Correct Answer :   Principle of moments

Explanation : The centre of pressure can be calculated using a principle of moments which states that the moment of the resultant force about an axis is equal to the sum of moments of the components about the same axis.

66 .
The circles with their centre on the X axis _________
A)
equal circles
B)
eccentric circles
C)
potential lines
D)
concentric circles

Correct Answer :   potential lines

Explanation : Potential lines are eccentric non-intersecting circles with their centres on x-axis. The potential lines for source pair will be eccentric non-intersecting circles.

67 .
Why the circular cylinder will create more drag?
A)
The pressure difference between downstream of flow
B)
The pressure difference between upstream and direction of flow
C)
The pressure difference between upstream and downstream direction of flow
D)
The pressure difference between relative wind and downstream direction of flow

Correct Answer :   The pressure difference between upstream and downstream direction of flow

Explanation : A circular cylinder produces large drag due to the pressure difference between upstream and downstream of the flow. The difference in pressure is causes by the periodic separation of flow over the surface of the cylinder. This will increase the drag in the cylinder.

68 .
How the cylinder will vibrate in the wind tunnel test?
A)
Due to low pressure
B)
Due to high pressure
C)
Due to relative pressure
D)
Due to fluctuations in the flow

Correct Answer :   Due to fluctuations in the flow

Explanation : The difference in pressure is caused by the periodic separation of flow over the surface of the cylinder. Periodic separation induces fluctuations in the flow and makes cylinder vibrate in the wind tunnel.

69 .
What is passive flow control method used to reduce the drag co-efficient over a cylinder?
A)
Wiring surfaces
B)
Roughened surfaces
C)
Surface framing
D)
Flow visualization

Correct Answer :   Roughened surfaces

Explanation : To reduce the amount of drag on a cylinder various active and passive flow control method have been employed and tested successfully.T hese method include dimpled surfaces, trip wires, roughened surfaces.

70 .
What is the reduction of drag by installing the small cylinder?
A)
48%
B)
55%
C)
75%
D)
95%

Correct Answer :   48%

Explanation : A 48% drag reduction of a cylinder by installing a much smaller cylinder in the upstream direction of flow. The shear layer coming from the smaller cylinder changes the pressure distribution around the layer cylinder in such a way that the drag is dramatically altered.

71 .
What are the quantitative flow visualization techniques?
A)
Surface framing
B)
Smoke flow visualization
C)
Shadow projecting
D)
Shadow graphic technique

Correct Answer :   Smoke flow visualization

Explanation : The visualization technique such as smoke flow visualization, surface oil film technique, particle image velocimetry have been employed to locate the position of transition and separation of a boundary layer.

72 .
What types of visualization is used to delay the separation of the flow?
A)
PVT
B)
Shadow projecting
C)
Smoke flow visualization
D)
Surface oil film technique

Correct Answer :   Smoke flow visualization

Explanation : Smoke flow visualization has been used by bakic and peric to visualize the delayed separation of the flow over a smooth sphere. The flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient.

73 .
How the finite lift is measured in the cylinder?
A)
Moving up
B)
Spinning cylinder
C)
Moving left and right
D)
Moving up and down

Correct Answer :   Spinning cylinder

Explanation : A finite lift is measured for the spinning cylinder in the wind tunnel.T he friction between the fluid and the surface of the cylinder tends to drag the fluid near the surface in the same direction as the rotational motion.

74 .
What is the position of stagnation point, when a cylinder is placed in the wind tunnel?
A)
Lower part
B)
Middle part
C)
Upper part
D)
No stagnation point

Correct Answer :   Lower part

Explanation : The stagnation point moves to the lower part of the cylinder, similar to the theoretical flow. If the spin is sufficiently increased the stagnation point lifts off the surface. Position of stagnation point is a strong function of circulation, with zero circulation stagnation point lies at zero.

75 .
How drag is formed on the cylinder?
A)
Due to friction
B)
Due to surface layer
C)
Due to boundary layer
D)
Due to viscous effect

Correct Answer :   Due to viscous effect

Explanation : Drag is due to a viscous effect, which generate a frictional shear stress at the body surface and which causes the flow to separate from the surface on the back of the body. At the leading edge of the cylinder, a stagnation point is formed. Where the oncoming flow is brought to rest. The pressure here is equal to the stagnation pressure. At the adjacent to the cylinder surface, a thin boundary layer is formed. Which causes the drag on the cylinder.

76 .
What is the lift on the cylinder?
A)
Zero
B)
One
C)
Negative
D)
Greater than zero

Correct Answer :   Zero

Explanation : Pressure distribution over the top half of the cylinder is equal to the pressure distribution over the bottom half and hence the lift must be zero. The air flows on the cylinder is deflected the same amount upward as the flow is deflected downwards at the rear of the cylinder. So the up wash equalizes the downwash in terms of resulting reaction forces. In the end, the free stream hasn’t been deflected at all but still, lift exists.

77 .
Is Kutta-Joukowski theorem relate to lift?
A)
True
B)
False
C)
Can Not Say
D)
None of the above

Correct Answer :   True

Explanation : The Kutta-Joukowski theorem relates the lift generated by an airfoil, to the speed of the airfoil. Through the fluid, the density of the fluid and the circulation. This theorem relates lift to circulation much like the Magnus effect relates to side force to the rotation.

78 .
Define circulation.
A)
Line integral of airfoil
B)
Line integral around an in loop enclosing the airfoil
C)
Line integral around a closed loop enclosing the airfoil
D)
Line integral around an open loop enclosing the airfoil

Correct Answer :   Line integral around a closed loop enclosing the airfoil

Explanation : Circulation is defined as the line integral around a closed loop enclosing the airfoil of the component of the velocity of the fluid tangent to the loop. To calculate the force on an airfoil, outside the boundary layer the vorticity is zero, everywhere the circulation is the same around every circuit.

79 .
Define Kutta-Joukowski theorem.
A)
Drag per unit span on the airfoil
B)
Lift per unit span on the airfoil
C)
Thrust per unit span on the airfoil
D)
Moment per unit span on the airfoil

Correct Answer :   Lift per unit span on the airfoil

Explanation : The Kutta-Joukowski theorem states that lift per unit span on a Two-Dimensional body, is directly propositional to the circulation around the body. It is a fundamental theorem of aerodynamics used for the calculation of the lift of an airfoil and any two-dimensional body.

80 .
What is the angle of attack of lift producing airfoil?
A)
Angle of attack is zero
B)
Angle of attack less than zero
C)
Angle of attack remains the same
D)
Angle of attack greater than zero

Correct Answer :   Angle of attack greater than zero

Explanation : A lift producing airfoil either has camber or is translating in a uniform fluid at an angle of attack greater than zero. Moreover, it must have a sharp trailing edge. An airfoil generates lift by exerting a downward force on the air as it flows past.

81 .
How the fluid moves on the airfoil?
A)
Upper surface
B)
Lower surface
C)
Upper and middle surface
D)
Lower and upper surface

Correct Answer :   Lower and upper surface

Explanation : Fluid moving along the lower and upper surface of the airfoil should meet at the sharp trailing edge. Since viscous dissipation prevents the fluid to turn around the sharp edge. This is known as the Kutta-Condition for real flow.

82 .
What is the condition for rotational flow in Kutta-Joukowski theorem?
A)
Large number of unsteady flow
B)
Small number of unsteady flow
C)
Large number of steady flow
D)
Small number of steady flow

Correct Answer :   Large number of unsteady flow

Explanation : When there are free vortices outside of the body as may be the case for a large number of unsteady flow, the flow is rotational. A fluid is said to be rotational if fluid particles are rotating about their own mass center, otherwise, flow is irrotational.

83 .
Kutta-Joukowski theorem refers to ________
A)
flows around an airfoil
B)
one-dimensional flow around an airfoil
C)
two-dimensional flow around an airfoil
D)
three-dimensional flow around an airfoil

Correct Answer :   two-dimensional flow around an airfoil

Explanation : Kutta-Joukowski theorem refers to Two-Dimensional flow around an airfoil and determines the lift generated by one unit of a span. Kutta-Joukowski theorem is an inviscid theory, but it is a good approximation for real viscous flow in typical aerodynamic applications.

84 .
How rotating flow is induced?
A)
Joint effect of airfoil
B)
Joint effect of camber
C)
Joint effect of chord
D)
Joint effect of camber line

Correct Answer :   Joint effect of camber

Explanation : Rotating flow is induced by the joint effect of camber, angle of attack and sharp trailing edge of the airfoil and should not be confused with a vortex like a tornado encircling the cylinder or wing of an airplane in flight.

85 .
What is the condition for Kutta and Joukowski theorem?
A)
Drag and lift
B)
Pressure and lift
C)
Lift and moment
D)
Pressure and drag

Correct Answer :   Pressure and lift

Explanation : Kutta and Joukowski discovered that for computing, the pressure and lift of a thin enough airfoil for flow with large enough Reynolds number and at small enough angle of attach the flow can be assumed inviscid in the entire region provided the Kutta condition is imposed.

86 .
What is the flow outside the airfoil?
A)
Constant
B)
Rotational
C)
Circumferential
D)
Irrotational

Correct Answer :   Irrotational

Explanation : The flow outside the airfoil is irrotational and the circulation around any closed curve not enclosing airfoil is consequently zero. When the boundary layer separates, its displacement thickness increases sharply, which modifies the outside potential flow and pressure field.

87 .
Purpose of non-lifting flow over an arbitrary body is _____
A)
to find a numerical method
B)
to find a drag body
C)
to find a lifting body
D)
to find a mathematical method

Correct Answer :   to find a numerical method

Explanation : The purpose of non-lifting flow over an arbitrary bodies is to find a numerical method for appropriate solution on a high speed digital computer. The technique is called the source panel. The numerical solution of potential flows by both source and vortex panel techniques has revolutionized the analyses of low speed flows.

88 .
Is arbitrary shape body can use in free stream velocity?
A)
True
B)
False
C)
Can Not Say
D)
None of the above

Correct Answer :   True

Explanation : Source sheet is used to cover the surface of the arbitrary body were the strength varies in such a fashion that the combined action of the uniform flow and the source sheet makes the airfoil surface as stream line of the flow.

89 .
Is vector (v) is positive when directed away from the body?
A)
True
B)
False
C)
Can Not Say
D)
None of the above

Correct Answer :   True

Explanation : The direction of the outward unit normal vector is positive when directed away from the body and it is carried out in the denominator at a singular point arises on the ith panel because the control point itself can be the contribution to the j=1 panel.

90 .
What is the normal component of the flow velocity at the rth control point?
A)
Sum of source line
B)
Sum of the sink line
C)
Sum of the freestream
D)
Sum of the source and sink line

Correct Answer :   Sum of the freestream

Explanation : The normal component of the flow velocity at the rth control point is the sum of that due to the free stream and that due to the source panels. The boundary condition stats that this sum must be zero and it is the cruse of the source panel method.

91 .
Why source strength 'X' per unit length is constant over a given panel?
A)
It remains in the same panel
B)
It allows it to varies from one panel to next panel
C)
The length will be changes from panel to panel
D)
It does not allow it to varies from one panel to next panel

Correct Answer :   It allows it to varies from one panel to next panel

Explanation : The source strength ‘X’ per unit length be constant over a given panel but allow it to vary from one panel to the next, that if there are total n panel. The source panel strength per unit length is ‘Xn’. Therefore boundary condition is imposed numerically by defining the midpoint of each panel.