Theory-based Quiz

Real Viscous Flows

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1 / 45

One of the assumption of the Blasius solution for laminar boundary layers is that:

There is no velocity variation in the fluid

There is no pressure variation in the fluid

The flow is unsteady

Mass is not conserved in the domain

2 / 45

Which of the following state variables are introduced using the second law of thermodynamics?

Pressure

Density

Temperature

Entropy

3 / 45

In which of the following cases is friction drag dominant?
(Select the two correct answers.)

A truck tractor with no trailer, driving on the highway

An open parachute slowing down a falling person

The wing of an airplane, at zero angle of attack with symmetrical crossection, cruising in air

A sail boat rudder aligned with the boat direction

4 / 45

For an inertially dominant flow, based on Prandtl's boundary layer theory, the effect of the viscosity is ________

Negligible outside the boundary layer

Negligible both inside and outside the boundary layer

Negligible inside the boundary layer

Non-negligible both inside and outside the boundary layer

5 / 45

Compared to the Blasius solution for a flat plate, the Falkner-Skan solution takes into account:

Non-zero pressure gradients

Swirl in the flow

Flow separation regions

Secondary flows

6 / 45

You were asked to analyze the flow of water (assumed incompressible) through a pipe with constant diameter and were told that the flow is fully-developed. Which of the following mean quantities do you expect to be remain constant along the length of the pipe?
(Select the three correct answers.)

Density

Centerline velocity

Pressure

Average velocity at any cross-section

7 / 45

Which of the following is a scope for analyzing external flows?

Estimating pressure losses across a system

Estimating the massflow rate through the volume of analysis

Estimating the forces exerted by the fluid on the body

Estimating the spatial average of velocity across the domain

8 / 45

Which of the following are examples of Internal flows?
(select the three correct answers.)

Oil flow through pipelines

Air flow around an locomotive

Blood flow through veins

Air flow through HVAC systems

9 / 45

Any turbulent flow property can be decomposed into the following two components:

A regular quasi-steady and an oscillating time-varying flow field

An incompressible and a compressible flow-field.

An inviscid and a viscous flow-field.

A Newtonian and a non-Newtonian flow-field.

10 / 45

Which of the following cases could be predicted by Reynolds stress models, while eddy viscosity models could fail?
(Select the two correct answers.)

Presence of secondary flows

Laminar flows

Flow over a flat plate

Swirl-dominated flows

11 / 45

Conduction heat transfer can occur in:
(Select the three correct answers.)

Solids

Gases

Liquids

Vaccuum

12 / 45

For a laminar flow over a flat plate, the shear stress is dependent on the following factors:

Free-stream velocity

Fluid viscosity

Fluid density

Flat plate thickness

13 / 45

In order to close the RANS equations ______ need to be modeled.

The skin-friction coefficients

The mean velocity terms

The pressure terms

The Reynolds stress terms

14 / 45

For a flat plate with a sharp leading edge, which of the following is the appropriate range of Reynolds number for the onset of turbulence, where $x$ is the distance from leading edge of the plate.

$Re_{x}=3.5 \times 10^{5} - 10 ^{6}$

$Re_{x}=3.5 \times 10^{1} - 10 ^{2}$

$Re_{x}=2000 - 4000 $

$Re_{x}=3.5 \times10^{2} - 10 ^{3}$

15 / 45

The minor losses at the entrance of a pipe, especially due to a sharp turn at the corner, are due to:

Turbulent flow

Flow separation

Laminar flow

Flow stagnation

16 / 45

In internal flows, fully-developed region refers to a region in which _______

Boundary layers merge and viscous effects are seen across the pipe

Boundary layers do not exist

Boundary layers separate from the wall

Boundary layers form and begin to grow on the walls

17 / 45

Which of the following can be considered as a minor loss in internal viscous flows?
(Select the three correct answers.)

Pressure loss arcoss a $90^o$ bend in a pipe.

Pressure loss due to sudden expansion

Pressure loss in a horizontal straight pipe of uniform diameter

Pressure loss due to sudden contraction

18 / 45

The point of separation of the boundary layer can be reasonably estimated by monitoring the location where ______ becomes approximately zero.

Pressure gradient

Density

Velocity gradient ($du/dy$)

Viscosity

19 / 45

When analyzing an object moving in a stationary reference frame, the no-slip condition on the object surface is defined as:

$\vec{U}=\vec{\omega} \times\vec{V}_t + \vec{r}$

$\vec{U}=\vec{\omega}\ \vec{r}\ \vec{V}_t$

$\vec{U}=\vec{\omega} r^2 $

$\vec{U}=\vec{\omega} \times \vec{r} +\vec{V}_t$

20 / 45

According to the Stefan-Boltzman law, the relationship between the emissive power ($E_b$) of an ideal blackbody and the absolute surface temperature ($T_s$) is:

$E_s \propto {T_s}^4$

$E_s \propto {T_s}^3$

$E_s \propto {T_s}$

$E_s \propto {T_s}^2$

21 / 45

For an external flow over a 2D cylinder the flow:

Separates at Reynolds numbers larger than about $10$

Separates at Reynolds number less than $1$

Never separates from the body

Does not separates at Reynolds numbers smaller than $10^6$

22 / 45

Analytical solutions can be obtained for external flows over:

Complex shapes at high Reynolds numbers

Complex shapes at very low Reynolds numbers

Simple shapes at high Reynolds numbers

Simple shapes at very low Reynolds numbers

23 / 45

The viscous losses in a laminar pipe flows do NOT depend on:

Pipe length

Surface roughness

Pipe diameter

Reynlods number

24 / 45

What is the thickness of a NACA 0015 airfoil profile, relative to its chord length?

$1\%$

$5\%$

$15\%$

$10\%$

25 / 45

When performing an analysis in the stationary ambient frame of a maneuvering vehicle, the velocity of the solid body ($\vec{V}_{solid}$) is:

Entirely defined by fluid and body forces

Externally prescribed and unaffected by the fluid forces

Defined by fluid and external forces

Defined only by fluid forces

26 / 45

When a laminar viscous fluid is flowing over a flat plate, the boundary layer thickness at distance $L$ on the flat plate is $\delta$. If we double the velocity of the fluid, the new boundary layer thickness at the same location of the flat plate, assuming the flow is still laminar, is:

Smaller than $\delta$

Larger than $\delta$

Equal to $\delta$

$0$

27 / 45

For a round pipe, if the flow is turbulent, the entrance length can be estimated as _____, where $D$ is the diameter of the pipe and $Re$ is the Reynolds number of the flow based on the diameter

$\frac{L_e}{D}\approx4.4Re^{6}$

$\frac{L_e}{D}\approx Re$

$\frac{L_e}{D}\approx 4.4Re^{1/6}$

$\frac{L_e}{D}\approx 0.06Re$

28 / 45

A boundary layer is a thin region near the ___________ where __________ effects are important.

Inlet, viscous

Wall, surface tension

Inlet, surface tension

Wall, viscous

29 / 45

For a fluid expanding suddenly into a pipe (as shown in the figure), which of the following statement are true?
(Select the three correct answers.)

A fully-developed flow is established right at the location where the diameter of the pipe suddenly changes

The fluid exiting the small diameter pipe initially exhibits a jet-like flow

The fluid looses kinetic energy during as it re-establishes the fully developed flow

A separation region is created where the diameter suddenly changes

30 / 45

In ________, heat is transferred from more energetic to less energetic particles because of molecular interactions.

Radiation

Natural convection

Forced convection

Conduction

31 / 45

In the context of laminar-turbulent transition, critical Reynolds number refers to the Reynolds number at which ______

Laminar-turbulent transition is completed and the flow is fully turbulent

Laminar-turbulent transition never happens and the flow is always turbulent

Laminar-turbulent transition never happens and the flow is always laminar

Laminar-turbulent transition is initiated and the flow enters the transition regime

32 / 45

For a straight leveled pipe the head loss is caused by:

Difference in height between the inlet and outlet

Shear stress

Gravity

Density

33 / 45

For a turbulent flow, which of the following statements are true regarding the small scale eddies?

The small scale eddies are statistically independent of the large scale eddies. this means that the small scale eddies are not dependent on the large scale flow characteristics

The small scale eddies are statistically dependent on the large scale eddies. this means that the small scale eddies are dependent on the large scale flow characteristics

Small scale eddies have a relatively small time-scales which are associated with their rotational frequency

Small scale eddies have a relatively large time-scales which are associated with their rotational frequency

34 / 45

Heat is always transferred:

Through a material

Between two objects with equal temperature

From a hot to a cold object

From a cold to a hot object

35 / 45

The wall shear stress exerted by a flow over any body acts:

Tangential to the body surface

Normal to the free-stream flow direction

Parallel to the free-stream flow direction

Normal to the body surface

36 / 45

According to Kutta-Joukowski theorem, any 2D body in relative motion to the ambient fluid with velocity $V$ has a lift force that is given by

$F=-\rho V_{\infty}^{-1}\Gamma$

$F=-\rho V_{\infty}\Gamma$

$F=-\rho V_{\infty}^3\Gamma$

$F=-\rho V_{\infty}^2\Gamma$

37 / 45

Compressibility is the inverse of

Bulk modulus

Young's modulus

Density

Shear modulus

38 / 45

The only mode of heat transfer occuring in vaccuum is:

Forced convection

Radiation

Conduction

Natural convection

39 / 45

The energy of the smaller eddies in a turbulent flow is converted into heat because of:

Pressure

Velocity

Density

Viscosity

40 / 45

In a CFD simulation of a viscous fluid flow over a 2D symmetric airfoil, the concept of boundary layers is important near the _____________

Plane of symmetry

Fluid inlet

Airfoil wall

Fluid outlet

41 / 45

Which of the following is an example of a jet?
(Select the three correct answers.)

Water flowingfrom a faucet into a kitchen sink

Smoke rising out of an industrial chimney

Gases ejected by the exhaust pipe of an automobile

Air flow in the ducts of a hvac unit

42 / 45

As a 2D laminar jet spreads, its centerline velocity decays as:

$x^{\frac{-2}{3}}$

$x^{\frac{-1}{3}}$

$x^{\frac{2}{3}}$

$x^{\frac{1}{3}}$

43 / 45

For a flat plate, the flow along the plate is considered entirely laminar if the Reynolds Number based on the length of flat plate:

$10^8< Re_L < 10^9$

$0 < Re_L < 10^6$

$10^7 < Re_L < 10^8$

$10^6 < Re_L < 10^7$

44 / 45

Which of the following have a direct impact on the laminar-turbulent transition in boundary layer? (Select the three correct answers.)

Surface roughness

Reynolds number

Surface color

Turbulence intensity

45 / 45

The cascade of energy from large to small eddies leads to:
(Select the two correct answers.)

Increasing the vorticity of the smaller eddies

Stretching of the small eddies because of the strain induced by the larger eddies

Decreasing the vorticity of the smaller eddies

Shrinking of the small eddies because of the strain induced by the larger eddies

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Real Viscous Flows

Total time - 60 mins.

Total number of Questions - 45