Aerodynamics Mcqs - Set 8

1)   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
Answer  Explanation 

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.


2)   Density is ratio of __________

a. mass to volume
b. volume to mass
c. mass to pressure
d. pressure to volume
Answer  Explanation 

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.


3)   The units of viscosity are __________

a. N/m
b. Ns/m2
c. m/s
d. Dimension less quantity
Answer  Explanation 

ANSWER: Ns/m2

Explanation:
The viscosity is defined as the property of the fluid which offers resistance to the movement of one layer over the other layer. It is shear stress required to produce unit rate of shear strain that is force*time/length2 that is Ns/m2.


4)   A combination of uniform flow and doublet flow gives ______________

a. flow past a circular cylinder
b. flow past a wedge
c. flow past a plate
d. flow over any body
Answer  Explanation 

ANSWER: flow past a circular cylinder

Explanation:
No explanation is available for this question!


5)   The stream function can be obtained by _______

a. sum of stream function of uniform flow and doublet flow
b. difference of stream function of uniform flow and doublet flow
c. sum of stream function of uniform flow and source flow
d. sum of stream function of uniform flow and sink flow
Answer  Explanation 

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.


6)   The flow past cylinder is also called as _________

a. Vortex flow
b. Source flow
c. Rankine oval of equal axes
d. Newton’s ring
Answer  Explanation 

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.


7)   The shape of Rankine oval of equal axes can be found out by substituting ______________

a. Ψ=0
b. Ψ=1
c. U=0
d. U=1
Answer  Explanation 

ANSWER: Ψ=0

Explanation:
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. This gives us two different solutions for which the shape of oval varies.


8)   What will be the shape of Rankine oval when sin θ=0?

a. vertical line
b. horizontal line
c. a point
d. curve
Answer  Explanation 

ANSWER: horizontal line

Explanation:
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.


9)   What will be the shape of Rankine oval when U*y+ ((-u/2*pi*r) = 0?

a. open curve
b. closed body profile
c. straight line
d. point
Answer  Explanation 

ANSWER: closed body profile

Explanation:
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.


10)   The amount of lift generated in the flow over a cylinder is __________

a. Infinity
b. Positive lift
c. Negative lift
d. No lift
Answer  Explanation 

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.


11)   In real life, zero drag is acceptable.

a. True
b. False
Answer  Explanation 

ANSWER: False

Explanation:
In real life, zero drag is not acceptable because we know that drag is produced due to viscous effects which generate frictional shear stress at the body surface and which cause the flow to separate from the surface on the back of the body and thus large wake downstream is created destroying the symmetry of the flow.


12)   The free vortex flow forms _________

a. straight lines
b. concentric circles
c. parabola
d. hyperbola
Answer  Explanation 

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.


13)   Except at the origin where r=0, the vortex flow is ___________

a. rotational
b. laminar
c. irrotational
d. turbulent
Answer  Explanation 

ANSWER: irrotational

Explanation:
Vortex flow is irrotational everywhere except at the point r=0, where the vorticity is infinite. Therefore, the origin, r=0, is a singular point in the flow field. Here, the origin point represents the singularity point.


14)   The strength of the vortex flow can be given by ______________

a. Γ=2*pi*C
b. Γ=2*pi
c. Γ=-2*pi*C
d. Γ=0
Answer  Explanation 

ANSWER: Γ=-2*pi*C

Explanation:
The circulation for vortex flow can be given by –
Γ=2*pi*C where, C – constant and Γ is the strength of the vortex flow.
When Γ is positive, it means that vortex of positive strength rotates in the clockwise direction and vice versa.


15)   The combination of uniform flow and source flow gives ___________

a. flow past a cylinder
b. flow past a half body
c. flow past a full body
d. flow past a wedge
Answer  Explanation 

ANSWER: flow past a half body

Explanation:
No explanation is available for this question!


16)   The circles with their centre on the X axis _____________

a. eccentric circles
b. concentric circles
c. potential lines
d. equal circles
Answer  Explanation 

ANSWER: potential lines

Explanation:
No explanation is available for this question!


17)   Centre of pressure can be calculated using __________

a. Principle of moments
b. Principle of energy
c. Mass conservation
d. Rayleigh’s principle
Answer  Explanation 

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.


18)   A body floats on the surface when ____________

a. metacenter is above gravity
b. metacenter is below gravity
c. metacenter is equal to gravity
d. gravity is above metacenter
Answer  Explanation 

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.


19)   Why the circular cylinder will create more drag?

a. The pressure difference between upstream and downstream direction of flow
b. The pressure difference between relative wind and downstream direction of flow
c. The pressure difference between upstream and direction of flow
d. The pressure difference between downstream of flow
Answer  Explanation 

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.


20)   How the cylinder will vibrate in the wind tunnel test?

a. Due to high pressure
b. Due to low pressure
c. Due to relative pressure
d. Due to fluctuations in the flow
Answer  Explanation 

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.