Question 1
Question
Under which circumstances may the volume rateofchange entail viscous shear stresses?
Answer

Never for incompressible flow.

Always under the Stokes hypothesis.

Always.

Never

None of the other options.
Question 2
Question
What is true about viscous blockage?
Answer

All options are correct.

It corresponds to a massflow reduction in the nearwall region due to the effects of viscosity

It corresponds to a momentum flux reduction in the nearwall region due to the effects of viscosity.

It follows from the noslip condition at the wall due to viscous effects.

It may be quantified by the displacement and momen
tum thicknesses of the boundary layer.
Question 3
Question
Which of the following factors may be held responsible for both advancing turbulent transition and inducing early separation of a boundary layer?
Answer

An adverse pressure gradient.

Wall roughness.

High preturbulence levels in the outer flow.

High Reynolds number.

None of the other options.
Question 4
Question
Laminar boundary layers, as opposed to turbulent,...
Answer

have lower friction but separate earlier.

have lower friction and separate later.

have higher friction and separate earlier

have higher friction but separate later.

None of the other options.
Question 5
Question
Which of the following properties of the NavierStokes equations do the Euler equations retain?
Answer

None of the other options.

The noslip condition can be applied on all solid walls.

They allow computation of friction drag.

They allow computation of form drag of closed bodies.

They can anticipate the occurrence of turbulence and
wakes.
Question 6
Question
Whichofthefollowingtermsofthestreamwisemomentum equation drops under the boundary layer hypothesis?
Question 7
Question
The boundary layer (BL) integral equations...
Answer

result from integrating the BL local equations in the wallnormal coordinate over the BL thickness.

result from integrating the BL local equations along the streamwise coordinate.

differ for laminar and turbulent BLs.

result in as many unknowns as there are equations.

None of the other options.
Question 8
Question
How is the D’Alembert’s paradox removed and the form drag obtained in an inviscid flow – boundary layer coupling calculation?
Answer

By solving the inviscid problem for a second time over a body enlarged by the displacement thickness and extended with the wake.

By directly solving the boundary layer equations.

The paradox remains no matter what.

By solving the inviscid problem over the original body.

The paradox was never there in the first place.
Question 9
Question
Which of the following inviscid potential flows admit self similar solutions for the twodimensional incompressible laminar boundary layer equations?
Question 10
Question
For the laminar boundary layer developing in the vicinity of a stagnation point...
Answer

momentum thickness is locally finite and constant.

displacement thickness grows linearly.

wall shear stress is locally finite and constant.

the form factor is larger than for the Blasius solution.

None of the other options.
Question 11
Question
Which of the following statements does NOT describe tur bulent flows?
Answer

Low energy dissipation.

Intrinsic threedimensionality.

Intrinsically timedependence.

Deterministic chaos.

Enhanced mixing capabilities.
Question 12
Question
Which of the following methods for solving turbulent flows simulates the large turbulent structures but filters out (and then models) the smaller scales?
Answer

Large Eddy Simulation (LES)

Reynolds Averaged NavierSokes (RANS).

Direct NavierStokes (DNS).

Direct Numerical Simulation (DNS).

None of the others.
Question 13
Question
What is the actual origin of the Reynolds stresses in the RANS equations?
Answer

Advective momentum transport due to turbulent fluc tuations.

Diffusive momentum transport due to enhanced fluid viscosity.

Turbulent pressure fluctuations.

Mass conservation in the presence of turbulent fluctu
ations.

None of the other options
Question 14
Question
How do viscous (foto)
compare within an incompressible, statistically twodimensional, turbulent boundary layer (TBL)?
Answer

mu*(du/dy) prevails in the inmediate vicinity of the wall.

densidad·u'·v' (tot adimensional) prevails over the full TBL thickness

mu*(du/dy) prevails over the full TBL thickness

densidad·u'·v' (tot adimensional) prevails in the inmediate vicinity of the wall.

They compete in size over the full TBL thickness.
Question 15
Question
What is the sign of the streamwisewallnormal velocity
fluctuation correlations (u'v') (adimensional todo) within a turbulent boundary
layer?
Answer

(u'v') (adimensional todo) < 0

(u'v') (adimensional todo) > 0

(u'v') (adimensional todo) = 0

(u'v') (adimensional todo) <0 close to the wall and (u'v') (adimensional todo) >0 far from it.

(u'v') (adimensional todo) >0 close to the wall and (u'v') (adimensional todo) <0 far from it.
Question 16
Question
How can lift be estimated for an airfoil immersed in inviscid incompressible flow?
Answer

By introducing a circulation to enforce the Kutta condition.

In no way because potential flow is irrotational.

Enforcing wall impermeability, lift naturally arises

By enforcing the noslip condition on the walls to the
potential flow equations.

None of the other options.
Question 17
Question
Which statement is true about the lifting problem within
the frame of linear potential theory?
Answer

The perturbation potential is antisymmetric in the
vertical coordinate.

The vertical perturbation velocity is antisymmetric
in the vertical coordinate.

Both the vertical and horizontal perturbation velocities are symmetric in the vertical coordinate

The horizontal perturbation velocity is symmetric in
the vertical coordinate.

None of the other options are correct.
Question 18
Question
A problem that aims at computing the pressure distribution given the airfoil shape is known as...
Question 19
Question
On a finite wing producing lift...
Answer

None of the other options are correct.

Wingtip vortices roll from suction to pressure side

The lift distribution is homogeneous along the span

There may still be no liftinduced drag

Streamlines are deflected towards the fuselage on the
pressure side and towards wingtip on the suction side.
Question 20
Question
Prandtl’s liftingline theory for finite wings...
Answer

All options are correct.

leads to an integrodifferential equation for the circulation distribution along the span.

shows that minimum liftinduced drag is obtained for
an elliptical distribution of circulation along the span.

is based on assessing the spandependent effective angle of attack that results from wingtip vortices.

provides both wing global lift and liftinduced drag
coefficients.
Question 21
Question
Into which terms may the total rateofchange of a small
fluid volume be split, provided nonlinear effects are neglected?
Answer

Translation, rotation, volume change, shear deformation.

Translation, rotation, volume change.

Translation, rotation, shear deformation.

Rotation, volume change, shear deformation.

Volume change, shear deformation.
Question 22
Question
Why is the drag on a sphere smaller when the separating
boundary layer is turbulent rather than laminar?
Answer

Because wake drag dominates and is smaller

Because friction drag dominates and is smaller.

Because both wake and friction drag are smaller.

Because wake drag is zero.

The assertion is plain wrong. The opposite is true.
Question 23
Question
23. What is true about the streamwise evolution of a boundary
layer (possibly involving a turbulent transition) developing
on a flat plate?
Answer

Its momentum thickness grows monotonically

Its friction coecient decreases monotonically

Its momentum thickness decreases monotonically.

Its friction coecient increases monotonically.

None of the other options.
Question 24
Question
Which statement is correct under the boundary layer hypothesis?
Answer

None of the other options.

Streamwise diffusion outweighs streamwise advection

Streamwise diffusion outweighs wallnormal diffusion.

Wallnormal pressure gradients are large.

Fluid particles slip at the wall.
Question 25
Question
Which of the following interpretations of the displacement
thickness is plain FALSE?
Answer

It quantifies the friction drag coefficient to be expected

It quantifies the deviation of streamlines outside of the
boundary layer

It quantifies the massflow blockage due to viscous effects.

It quantifies the amount of wallnormal momentum
that must appear for mass preservation within the
boundary layer.

All statements are TRUE
Question 26
Question
26. Which of the following boundary layers is at a higher risk
of separation, all other parameters unaltered?
Answer

One that has a larger thickness

One that has a larger outer velocity

One that is subject to a stronger negative (favorable)
pressure gradient.

One that is turbulent.

One that is subject to a milder deceleration of the
outer flow
Question 27
Question
27. What are the usual assumptions in order to devise an integral method for both laminar and turbulent boundary
layers?
Answer

H and Cf/2 Re o taken from flat plate values

H and Cf/2 Re o taken from stagnation point values.

H and Cf/2 Re o taken from separation profile values.

H taken from stagnation point and Cf/2 Re o from separation profile values

H taken from flat plate and Cf/2 Re o from stagnation
point values.
Question 28
Question
28. Which term of the NavierStokes equations is responsible
for the appearance of the Reynolds stresses in the RANS
equations?
Question 29
Question
29. Which of the following statements is true about the
Reynolds stresses inside a turbulent, statistically twodimensional, incompressible boundary layer?
Question 30
Question
Pregunta 30 To which of the following regions in a turbulent boundary layer does the near wall hypothesis (constant shear
@⌧/@y ' 0, linear mixing length l ' y+) apply?
Question 31
Question
31. What does viscosity depend on for Newtonian fluids such
as water or air?
Question 32
Question
32. Which of the following conditions entails separation of a
twodimensional flow?
Answer

Zero wall friction

Zero wall velocity

Infinite wallnormal gradient of streamwise velocity

Zero boundary layer momentum thickness

Zero boundary layer form factor.
Question 33
Question
Which momentum transport mechanisms are mainly competing within a laminar boundary layer?
Answer

Streamwise advection and wallnormal diffusion

Streamwise diffusion and wallnormal advection

Streamwise diffusion and streamwise advection.

Wallnormal advection and wallnormal diffusion.

Wallnormal and streamwise diffusion.
Question 34
Question
34. How are the integral boundary layer equations obtained?
Answer

By integrating the local equations over the boundary
layer thickness.

By integrating the local equations along the streamwise coordinate.

By searching for selfsimilar solutions of the local
equations

By applying the boundary layer hypothesis to the
NavierStokes equations in their integral form.

By adding whole wheat to the fluid.
Question 35
Question
35. How does the momentum thickness evolve for a laminar
boundary layer in the close vicinity of a stagnation point?
Answer

It is finite and constant.

It remains of negligible size.

It debuts with a finite value and grows linearly.

It debuts at zero and grows linearly

It debuts at infinity and decreases hyperbolically
Question 36
Question
What can be said about the friction coecient Cf when
comparing growing laminar and turbulent boundary layers (BLs) developing under the same outer velocity conditions?
Answer

It is higher and decreases slowlier for turbulent BL.

It is higher and decreases slowlier for laminar BL.

It is higher but decreases faster for turbulent BL.

It is higher but decreases faster for laminar BL.

None of the others.
Question 37
Question
37. Theoreticalempirical turbulent friction laws result from
the matching of the velocity profile in what regions/layers
of the turbulent boundary layer universal profile?
Answer

Inner and outer regions

Viscous sublayer and buffer region

Buffer region and loglaw layer

Viscous sublayer and loglaw layer

Buffer region and inner region.
Question 38
Question
38. Which of the following phenomena can be ultimately ascribed to the action of viscosity?
Answer

All of them

Lift

Friction drag

Wake drag

Flow separation
Question 39
Question
39. Which of the following actions might be beneficial in terms
of drag coefficient reduction of a streamlined body (e.g.
flat plate at alpha = 0) with a laminar boundary layer naturally developing on its surface?
Answer

Preserving laminarity of the boundary layer all the
way down to the trailing edge.

Artificially triggering turbulent transition in the
boundary layer before it separates.

Reducing the Reynolds number

Favouring surface rugosity.

None of the others.
Question 40
Question
40. Which of the following is NOT a consequence of the boundary layer hypothesis?
Answer

Negligible streamwise advection

Wallnormal pressure gradient must cancel.

The local BL equations are parabolic

Negligible streamwise diffusion

Streamwise velocity outweighs wallnormal velocity.
Question 41
Question
41. When do boundary layers grow faster?
Answer

In adverse pressure gradient conditions

In favourable pressure gradient conditions.

In conditions of accelerated outer flow.

In conditions of accelerated (decelerated) outer flow if
the boundary layer is laminar (turbulent).

In adverse (favourable) pressure gradient conditions if
the boundary layer is laminar (turbulent).
Question 42
Question
Upon averaging which term of the NavierStokes equations
does the Reynolds stress tensor arise?
Answer

Advection term

Diffusion term.

Timederivative term.

Pressure gradient term.

None of the others.
Question 43
Question
43. What is true when comparing solution methods for laminar and turbulent boundary layers (BLs)?
Answer

The BL integral equations are formally the same.

The BL local equations are formally the same.

The FalknerSkan selfsimilar solutions apply all the
same, provided that the outer flow is a wedge flow.

Experimental input is needed for solving both laminar
and turbulent BLs.

All of the others.