# Aerodynamics Questions and Answers – Pathlines, Streamlines, Streaklines

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

**1. Which of the following are the imaginary lines?**

**a) Streamline and pathline**

b) Pathline and streakline

c) Streamline and streakline

d) Only streamline

**Explanation**: Because a streamline depicts the direction of fluid flow from a specific point in the fluid flow domain, both Streamlines and Pathlines are imaginary. This imaginary point can be found everywhere in the fluid domain. The path traced by a fluid element at a certain time interval is called a pathline.

**2. In steady flow, streamline, streakline, pathline are the same.**

**a) True**

b) False

**Explanation: **The steady flow is defined as a flow in which the flow velocity does not fluctuate over time and so the flow remains constant. Throughout the flow, the pathline, streamline, and streakline remain the same.

**3. The pathline equation is ______**

a) y = x^{t}

**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=t

^{2/2}

On substituting the above values we get, 2 lnY = (ln x)

^{2}.

**4. 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:** The velocity of a steady flow remains constant over time. As a result, the velocity remains constant, dy/dx=y/x. When we integrate the preceding equation, we get x=y, which establishes that given a constant flow with the same velocity field, the pathline and streamline are the same.

**5. In an unsteady flow, the equation of streamline is given by __________**

a) x=y

b) y=0

c) y=0

**d) y=x ^{t}**

**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=x

^{t}.

**6. Which of the following is not related to the streamlines?**

**a) Mass**

b) Velocity

c) Fluid flow

d) Fluid domain

**Explanation:** Mass is unrelated to streamlines since the velocity has no normal component, it travels in a straight line with no normal components, and so the mass cannot cross the streamline.

**7. 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:** The streamlines obtained when a curve, line, or closed curve is utilised as a starting point are referred to as a stream surface. The Stream function, which determines the scalar function of these streamlines, is used in this scenario.

**8. The streamlines depend on the frame of reference.**

**a) true**

b) false

**Explanation:** The streamlines are dependent on the frame. It is dependent on the frame of reference from which it is perceived. It varies depending on the inertial reference frame you’re looking at. The flow over an aircraft, for example, will be different for those inside the plane and those on the ground.

**9. 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:** Lines in the fluid domain are known as streamlines. The direction of velocity of the fluid particle is determined by drawing tangents from these lines. As a result, when Ram visualised the spots in the fluid and drew tangents from those locations, he was able to perceive the streamlines.

**10. 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.

**11. The smoke particles coming out from the chimney falls under ____________**

a) Streamline

**b) Streakline**

c) Path line

d) Position vector

**Explanation:** The streakline is the location of a particle that has previously passed through a fixed point. In the case of the chimney, the fixed point is the chimney, and the locus is the smoke that travels through it. The smoke’s route can be followed.

Field lines in a fluid flow are streamlines, streaklines, and pathlines. They only differ when the flow varies over time, i.e. when the flow is not constant. Streaklines are the sites where all the fluid particles that have travelled through a specific spatial point in the past have collided. Because a streamline depicts the direction of fluid flow from a specific point in the fluid flow domain, both Streamlines and Pathlines are imaginary. This imaginary point can be found everywhere in the fluid domain. The path traced by a fluid element at a certain time interval is called a pathline.