Aerodynamics Questions and Answers – Pathlines, Streamlines, Streaklines

This set of Aerodynamics Interview Questions and Answers focuses on “Pathlines, Streamlines, Streaklines”.

1. Ram was on the bank of the river and was observing the flow of river. After sometime he got an idea and he started imagining certain points in the fluid and when he drew tangent to those points, he got direction of the flow. These lines are called as _____________
a) Streakline
b) Pathline
c) Streamline
d) Velocity vector

Explanation: Streamlines are the lines in fluid domain. When tangents are drawn from these lines, it gives the direction of velocity of the fluid particle. Hence, when Ram started imagining the points in the fluid and when he drew tangents from those points he could actually see the streamlines.

2. In the figure shown below, what does the fluid particle ‘A’ represents from t=0 to t=t?

a) Streamline
b) Streakline
c) Pathline
d) Velocity vector

Explanation: Pathline is defined as the path traced by a particular fluid particle in some given time interval. The fluid particle ‘A’ at t=0 travels till t=t.

3. The smoke particles coming out from the chimney falls under ____________
a) Streamline
b) Streakline
c) Path line
d) Position vector

Explanation: Streakline is defined as the locus of the particle that has earlier passed through the fixed point. In the case of the chimney, the chimney is the fixed point and the smoke which passes through it makes the locus. The path of the smoke can be traced.

4. Which of the following are the imaginary lines?
a) Streamline and pathline
b) Pathline and streakline
c) Streamline and streakline
d) Only streamline

Explanation: Both Streamlines and pathline are imaginary because streamline represents the direction of the fluid flow from a particular point in the fluid flow domain. This point can be anywhere in the fluid domain and is imaginary. Pathline is the path traced by a fluid element at a given interval of the time.

5. In steady flow, streamline, streakline, pathline are the same.
a) True
b) False

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.
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6. The pathline equation is ______
a) y = xt
b) 2ln y = (ln x)2
c) x = y
d) x = -1 + y

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.

7. In steady state flow, the equation for streamline can be given by ________
a) x=0
b) y=0
c) x=y
d) x=-1

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.

8. In an unsteady flow, the equation of streamline is given by __________
a) x=y
b) y=0
c) y=0
d) 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.

9. Which of the following is not related to the streamlines?
a) Mass
b) Velocity
c) Fluid flow
d) Fluid domain

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.

10. 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

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.

11. The streamlines depend on the frame of reference.
a) true
b) false

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.

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