Quiz
AERO FQ ALBERT (1/3)
Questions in this quiz (43)
1Under which circumstances may the volume rate-of-change entail viscous shear stresses?
- ANever for incompressible flow.
- BAlways under the Stokes hypothesis.
- CAlways.
- DNever
- ENone of the other options.
2What is true about viscous blockage?
- AAll options are correct.
- BIt corresponds to a massflow reduction in the near-wall region due to the effects of viscosity
- CIt corresponds to a momentum flux reduction in the near-wall region due to the effects of viscosity.
- DIt follows from the no-slip condition at the wall due to viscous effects.
- EIt may be quantified by the displacement and momen-
tum thicknesses of the boundary layer.
3Which of the following factors may be held responsible for both advancing turbulent transition and inducing early separation of a boundary layer?
- AAn adverse pressure gradient.
- BWall roughness.
- CHigh preturbulence levels in the outer flow.
- DHigh Reynolds number.
- ENone of the other options.
4Laminar boundary layers, as opposed to turbulent,...
- Ahave lower friction but separate earlier.
- Bhave lower friction and separate later.
- Chave higher friction and separate earlier
- Dhave higher friction but separate later.
- ENone of the other options.
5Which of the following properties of the Navier-Stokes equations do the Euler equations retain?
- ANone of the other options.
- BThe no-slip condition can be applied on all solid walls.
- CThey allow computation of friction drag.
- DThey allow computation of form drag of closed bodies.
- EThey can anticipate the occurrence of turbulence and
wakes.
6Whichofthefollowingtermsofthestreamwisemomentum equation drops under the boundary layer hypothesis?
- AStreamwise diffusion.
- BWall-normal diffusion.
- CStreamwise advection.
- DWall-normal advection.
- EStreamwise pressure gradient.
7The boundary layer (BL) integral equations...
- Aresult from integrating the BL local equations in the wall-normal coordinate over the BL thickness.
- Bresult from integrating the BL local equations along the streamwise coordinate.
- Cdiffer for laminar and turbulent BLs.
- Dresult in as many unknowns as there are equations.
- ENone of the other options.
8How is the D’Alembert’s paradox removed and the form drag obtained in an inviscid flow – boundary layer coupling calculation?
- ABy solving the inviscid problem for a second time over a body enlarged by the displacement thickness and extended with the wake.
- BBy directly solving the boundary layer equations.
- CThe paradox remains no matter what.
- DBy solving the inviscid problem over the original body.
- EThe paradox was never there in the first place.
9Which of the following inviscid potential flows admit self- similar solutions for the two-dimensional incompressible laminar boundary layer equations?
- AWedge/corner flows.
- BSource and sink flows.
- CIrrotational vortex flow.
- DDoublet flow.
- ENone of the other options.
10For the laminar boundary layer developing in the vicinity of a stagnation point...
- Amomentum thickness is locally finite and constant.
- Bdisplacement thickness grows linearly.
- Cwall shear stress is locally finite and constant.
- Dthe form factor is larger than for the Blasius solution.
- ENone of the other options.
11Which of the following statements does NOT describe tur- bulent flows?
- ALow energy dissipation.
- BIntrinsic three-dimensionality.
- CIntrinsically time-dependence.
- DDeterministic chaos.
- EEnhanced mixing capabilities.
12Which of the following methods for solving turbulent flows simulates the large turbulent structures but filters out (and then models) the smaller scales?
- ALarge Eddy Simulation (LES)
- BReynolds Averaged Navier-Sokes (RANS).
- CDirect Navier-Stokes (DNS).
- DDirect Numerical Simulation (DNS).
- ENone of the others.
13What is the actual origin of the Reynolds stresses in the RANS equations?
- AAdvective momentum transport due to turbulent fluc- tuations.
- BDiffusive momentum transport due to enhanced fluid viscosity.
- CTurbulent pressure fluctuations.
- DMass conservation in the presence of turbulent fluctu-
ations. - ENone of the other options
14How do viscous (foto)
compare within an incompressible, statistically twodimensional, turbulent boundary layer (TBL)?
- Amu*(du/dy) prevails in the inmediate vicinity of the wall.
- B-densidad·u'·v' (tot adimensional) prevails over the full TBL thickness
- Cmu*(du/dy) prevails over the full TBL thickness
- D-densidad·u'·v' (tot adimensional) prevails in the inmediate vicinity of the wall.
- EThey compete in size over the full TBL thickness.
15What is the sign of the streamwise-wall-normal velocity
fluctuation correlations (u'v') (adimensional todo) within a turbulent boundary
layer?- A(u'v') (adimensional todo) < 0
- B(u'v') (adimensional todo) > 0
- C(u'v') (adimensional todo) = 0
- D(u'v') (adimensional todo) <0 close to the wall and (u'v') (adimensional todo) >0 far from it.
- E(u'v') (adimensional todo) >0 close to the wall and (u'v') (adimensional todo) <0 far from it.
16How can lift be estimated for an airfoil immersed in inviscid incompressible flow?
- ABy introducing a circulation to enforce the Kutta condition.
- BIn no way because potential flow is irrotational.
- CEnforcing wall impermeability, lift naturally arises
- DBy enforcing the no-slip condition on the walls to the
potential flow equations. - ENone of the other options.
17Which statement is true about the lifting problem within
the frame of linear potential theory?- AThe perturbation potential is anti-symmetric in the
vertical coordinate. - BThe vertical perturbation velocity is anti-symmetric
in the vertical coordinate. - CBoth the vertical and horizontal perturbation velocities are symmetric in the vertical coordinate
- DThe horizontal perturbation velocity is symmetric in
the vertical coordinate. - ENone of the other options are correct.
- AThe perturbation potential is anti-symmetric in the
18A problem that aims at computing the pressure distribution given the airfoil shape is known as...
- Aa direct problem
- Ban inverse problem
- Ca symmetric problem.
- Dan anti-symmetric problem
- ENone of the others options are correct.
19On a finite wing producing lift...
- ANone of the other options are correct.
- BWingtip vortices roll from suction to pressure side
- CThe lift distribution is homogeneous along the span
- DThere may still be no lift-induced drag
- EStreamlines are deflected towards the fuselage on the
pressure side and towards wingtip on the suction side.
20Prandtl’s lifting-line theory for finite wings...
- AAll options are correct.
- Bleads to an integro-differential equation for the circulation distribution along the span.
- Cshows that minimum lift-induced drag is obtained for
an elliptical distribution of circulation along the span. - Dis based on assessing the span-dependent effective angle of attack that results from wingtip vortices.
- Eprovides both wing global lift and lift-induced drag
coefficients.
21Into which terms may the total rate-of-change of a small
fluid volume be split, provided nonlinear effects are neglected?- ATranslation, rotation, volume change, shear deformation.
- BTranslation, rotation, volume change.
- CTranslation, rotation, shear deformation.
- DRotation, volume change, shear deformation.
- EVolume change, shear deformation.
22Why is the drag on a sphere smaller when the separating
boundary layer is turbulent rather than laminar?- ABecause wake drag dominates and is smaller
- BBecause friction drag dominates and is smaller.
- CBecause both wake and friction drag are smaller.
- DBecause wake drag is zero.
- EThe assertion is plain wrong. The opposite is true.
2323. What is true about the streamwise evolution of a boundary
layer (possibly involving a turbulent transition) developing
on a flat plate?- AIts momentum thickness grows monotonically
- BIts friction coecient decreases monotonically
- CIts momentum thickness decreases monotonically.
- DIts friction coecient increases monotonically.
- ENone of the other options.
24 Which statement is correct under the boundary layer hypothesis?
- ANone of the other options.
- BStreamwise diffusion outweighs streamwise advection
- CStreamwise diffusion outweighs wall-normal diffusion.
- DWall-normal pressure gradients are large.
- EFluid particles slip at the wall.
25Which of the following interpretations of the displacement
thickness is plain FALSE?- AIt quantifies the friction drag coefficient to be expected
- BIt quantifies the deviation of streamlines outside of the
boundary layer - CIt quantifies the massflow blockage due to viscous effects.
- DIt quantifies the amount of wall-normal momentum
that must appear for mass preservation within the
boundary layer. - EAll statements are TRUE
2626. Which of the following boundary layers is at a higher risk
of separation, all other parameters unaltered?- AOne that has a larger thickness
- BOne that has a larger outer velocity
- COne that is subject to a stronger negative (favorable)
pressure gradient. - DOne that is turbulent.
- EOne that is subject to a milder deceleration of the
outer flow
2727. What are the usual assumptions in order to devise an integral method for both laminar and turbulent boundary
layers?- AH and Cf/2 Re o taken from flat plate values
- BH and Cf/2 Re o taken from stagnation point values.
- CH and Cf/2 Re o taken from separation profile values.
- DH taken from stagnation point and Cf/2 Re o from separation profile values
- EH taken from flat plate and Cf/2 Re o from stagnation
point values.
2828. Which term of the Navier-Stokes equations is responsible
for the appearance of the Reynolds stresses in the RANS
equations?- AThe advection term
- BThe pressure term.
- CThe time-derivative term.
- DThe viscous diffusion term.
- EThe volume forces term.
2929. Which of the following statements is true about the
Reynolds stresses inside a turbulent, statistically twodimensional, incompressible boundary layer?- Au'v' (adim) < 0
- Bv'^2 adim > u'^2 adimd
- Cw'^2 adim = 0
- Du'v' (adim) =/ 0 at the wall
- Eu'^2 v'^2 w'^2 (adim) =/ 0
30Pregunta 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?
- AAll options are correct.
- BTo the inner region.
- CTo the viscous sublayer.
- DTo the buffer/overlap/blending region
- ETo the log-law layer.
3131. What does viscosity depend on for Newtonian fluids such
as water or air?- ATemperature
- BShear deformation rate.
- CBoth temperature and shear deformation rate.
- DNeither temperature nor shear deformation rate.
- EReynolds number
3232. Which of the following conditions entails separation of a
two-dimensional flow?- AZero wall friction
- BZero wall velocity
- CInfinite wall-normal gradient of streamwise velocity
- DZero boundary layer momentum thickness
- EZero boundary layer form factor.
33Which momentum transport mechanisms are mainly competing within a laminar boundary layer?
- AStreamwise advection and wall-normal diffusion
- BStreamwise diffusion and wall-normal advection
- CStreamwise diffusion and streamwise advection.
- DWall-normal advection and wall-normal diffusion.
- EWall-normal and streamwise diffusion.
3434. How are the integral boundary layer equations obtained?
- ABy integrating the local equations over the boundary
layer thickness. - BBy integrating the local equations along the streamwise coordinate.
- CBy searching for self-similar solutions of the local
equations - DBy applying the boundary layer hypothesis to the
Navier-Stokes equations in their integral form. - EBy adding whole wheat to the fluid.
- ABy integrating the local equations over the boundary
3535. How does the momentum thickness evolve for a laminar
boundary layer in the close vicinity of a stagnation point?- AIt is finite and constant.
- BIt remains of negligible size.
- CIt debuts with a finite value and grows linearly.
- DIt debuts at zero and grows linearly
- EIt debuts at infinity and decreases hyperbolically
36What can be said about the friction coecient Cf when
comparing growing laminar and turbulent boundary layers (BLs) developing under the same outer velocity conditions?- AIt is higher and decreases slowlier for turbulent BL.
- BIt is higher and decreases slowlier for laminar BL.
- CIt is higher but decreases faster for turbulent BL.
- DIt is higher but decreases faster for laminar BL.
- ENone of the others.
3737. Theoretical-empirical turbulent friction laws result from
the matching of the velocity profile in what regions/layers
of the turbulent boundary layer universal profile?- AInner and outer regions
- BViscous sublayer and buffer region
- CBuffer region and log-law layer
- DViscous sublayer and log-law layer
- EBuffer region and inner region.
3838. Which of the following phenomena can be ultimately ascribed to the action of viscosity?
- AAll of them
- BLift
- CFriction drag
- DWake drag
- EFlow separation
3939. 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?- APreserving laminarity of the boundary layer all the
way down to the trailing edge. - BArtificially triggering turbulent transition in the
boundary layer before it separates. - CReducing the Reynolds number
- DFavouring surface rugosity.
- ENone of the others.
- APreserving laminarity of the boundary layer all the
4040. Which of the following is NOT a consequence of the boundary layer hypothesis?
- ANegligible streamwise advection
- BWall-normal pressure gradient must cancel.
- CThe local BL equations are parabolic
- DNegligible streamwise diffusion
- EStreamwise velocity outweighs wall-normal velocity.
4141. When do boundary layers grow faster?
- AIn adverse pressure gradient conditions
- BIn favourable pressure gradient conditions.
- CIn conditions of accelerated outer flow.
- DIn conditions of accelerated (decelerated) outer flow if
the boundary layer is laminar (turbulent). - EIn adverse (favourable) pressure gradient conditions if
the boundary layer is laminar (turbulent).
42Upon averaging which term of the Navier-Stokes equations
does the Reynolds stress tensor arise?- AAdvection term
- BDiffusion term.
- CTime-derivative term.
- DPressure gradient term.
- ENone of the others.
4343. What is true when comparing solution methods for laminar and turbulent boundary layers (BLs)?
- AThe BL integral equations are formally the same.
- BThe BL local equations are formally the same.
- CThe Falkner-Skan self-similar solutions apply all the
same, provided that the outer flow is a wedge flow. - DExperimental input is needed for solving both laminar
and turbulent BLs. - EAll of the others.
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- Quiz on AERO FQ ALBERT (1/3), created by Albert Font on 13/01/2020.
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- Albert Font
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