1) In steady flow, streamline, streakline, pathline are the same.
a. True
b. False
|
Answer
Explanation
|
ANSWER: True
Explanation:
The steady flow refers to the flow in which the flow velocity does not change with respect to the time and so the flow remains constant throughout. The pathline, streamline and the streakline also remains the same throughout the flow.
|
|
2) The pathline equation is ______
a. y = xt
b. 2ln y = (ln x)²
c. x = y d. x = -1 + y
|
Answer
Explanation
|
ANSWER: 2ln y = (ln x)²
Explanation:
dX/dt=U, dY/dt=V, dZ/dt=W
Consider the velocity vector,
V= Xi+Yj
T=0, U=X and V=Y*t
ln X=t and ln Y=t²/²
On substituting the above values we get, 2 lnY = (ln x)².
|
|
3) In steady state flow, the equation for streamline can be given by ________
a. x=0
b. y=0
c. x=y d. x=-1
|
Answer
Explanation
|
ANSWER: x=y
Explanation:
In steady flow, the velocity does not change with respect to time. Hence, the velocity remains constant that is dy/dx=y/x. On integrating the above equation we get, x=y, which proves that pathline and streamline are same for steady flow with same velocity field.
|
|
4) In an unsteady flow, the equation of streamline is given by __________
a. x=y
b. y=0
c. y=0 d. y=xt
|
Answer
Explanation
|
ANSWER: y=xt
Explanation:
Consider the velocity vector, V= xi +y*tj
Here u=x and v=y*t
We know that dx/u=dy/v=dz/w
On substituting the vales and integrating, we get, y=xt.
|
|
5) Which of the following is not related to the streamlines?
a. Mass
b. Velocity
c. Fluid flow d. Fluid domain
|
Answer
Explanation
|
ANSWER: Mass
Explanation:
Mass is not related to the streamlines because the velocity does not have normal component, it flows in a straight direction and does not have any normal components either and hence, the mass cannot cross the streamline.
|
|
6) Seeta used a closed curve as her start point, it will result in the ___________
a. plane
b. stream surface
c. stream line d. stream plane
|
Answer
Explanation
|
ANSWER: stream surface
Explanation:
If a curve, line or closed curve is used as a start point then the streamlines so obtained are called a stream surface. In this case, Stream function comes into the picture which defines the scalar function of these streamlines.
|
|
7) The streamlines depend on the frame of reference.
a. true
b. false
|
Answer
Explanation
|
ANSWER: true
Explanation:
The streamlines are frame dependent. It depends on the reference frame from which it is being observed. It differs from one inertial reference frame to another inertial reference frame. For example, the flow over an aircraft will be different for the people inside the aircraft and for the people on the ground.
|
|
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
|
Answer
Explanation
|
ANSWER: Angular velocity
Explanation:
Angular velocity comes in the picture when the flow is rotational that is the flow which has both translational as well as rotational motion. It is the rate of change of angular displacement. It is denoted by omega and its SI unit id 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
|
Answer
Explanation
|
ANSWER: True
Explanation:
An element may undergo distortion because when a body translates n rotate some of its parts me undergo external forces because of the shape of the element may change. The amount of distortion depends on 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)
|
Answer
Explanation
|
ANSWER: ω = 0.5(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.
|
|
11) The term 2*ω is called as _____________
a. Velocity
b. Divergence
c. Angular velocity d. Vorticity
|
Answer
Explanation
|
ANSWER: Divergence
Explanation:
Vorticity is twice the angular velocity. The angular velocity of the fluid plays an important role in theoretical aerodynamics and 2*ω occurs frequently and in order to reduce the complexity, we use vorticity.
|
|
12) The curl of velocity equals to _______
a. velocity
b. pressure
c. vorticity d. angular velocity
|
Answer
Explanation
|
ANSWER: vorticity
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.
|
|
13) If ∇*V is not equal to zero, then the flow is __________
a. steady
b. unsteady
c. rotational d. irrotational
|
Answer
Explanation
|
ANSWER: rotational
Explanation:
In rotational flow, the fluid element has a finite angular velocity which means the element can undergo rotation and as well as distortion. The amount of distortion depends on the velocity field.
|
|
14) If ∇*V is equal to zero, then the flow is _________
a. steady
b. unsteady
c. rotational d. irrotational
|
Answer
Explanation
|
ANSWER: irrotational
Explanation:
In irrotational flow, the fluid element does not have a finite angular velocity which means the element cannot undergo rotation and as well as distortion. The motion of the fluid element is purely translational motion.
|
|
15) The subsonic flow over an airfoil is an example of __________
a. steady
b. unsteady
c. rotational d. irrotational
|
Answer
Explanation
|
ANSWER: irrotational
Explanation:
For the subsonic flow over an airfoil, the flow is irrotational which means the motion of the fluid element is translational. In such cases, a thin boundary layer is formed around the surface. In this boundary layer, the flow is highly rotational whereas, outside the boundary layer it is irrotational.
|
|
16) The angle between the two lines (x and y direction) is called as ___________
a. viscous layer
b. strain
c. stress d. velocity vector
|
Answer
Explanation
|
ANSWER: strain
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.
|
|
17) The absence of vorticity means the flow is ________
a. steady
b. unsteady
c. rotational d. irrotational
|
Answer
Explanation
|
ANSWER: irrotational
Explanation:
The absence of vorticity means the flow is irrotational flow, which simplifies the flow analysis. This is greatly used in case of inviscid flows. The flow analysis becomes easy for irrotational flow since there is no rotational motion of the fluid element.
|
|
18) The line integral of a closed curve around of a velocity field is defined as____________
a. Vorticity
b. Circulation
c. Dilatation d. Streamline
|
Answer
Explanation
|
ANSWER: Circulation
Explanation:
Circulation is the line integral of the velocity around a closed curve in the flow. It depends on the velocity field and the selection of the curve. It defines the movement of the flow inside the curve. It is given by-
Γ=∮c V. ds where, Γ- circulation, ∮c – curve, V.ds – velocity field.
|
|
19) If the flow is irrotational everywhere within the contour of integration then the circulation is ____________
a. 1
b. positive
c. negative d. zero
|
Answer
Explanation
|
ANSWER: zero
Explanation:
In the case of irrotational flow, the circulation about a curve is equal to the vorticity integrated over any open surface bounded by the curve. This leads to the result that if the flow is irrotational everywhere, the circulation is zero.
|
|
20) The component of vorticity normal to dS is equal to __________
a. circulation per unit area
b. negative of circulation per unit area
c. zero d. circulation
|
Answer
Explanation
|
ANSWER: negative of circulation per unit area
Explanation:
The relation between circulation and vorticity can be given by-
(∇*V).n = -dΓ/dS
Where dS – infinitesimal area enclosed
C – Infinitesimal curve.
|
|
