Test 32 - Boundary Layer Separation

Question 1 ప్రశ్న 1

Which statement best describes boundary-layer separation from a solid surface?

A A condition in which the external inviscid velocity becomes zero everywhere B Detachment of the boundary-layer flow from the surface after the near-wall fluid loses sufficient streamwise momentum C A condition in which viscosity suddenly becomes zero D The normal growth of an attached boundary layer over a flat plate

Question 2 ప్రశ్న 2

For incompressible external flow with x measured downstream, which combination represents a favourable pressure gradient?

A dp/dx > 0 and dUe/dx < 0 B dp/dx = 0 and dUe/dx < 0 C dp/dx < 0 and dUe/dx > 0 D dp/dx > 0 and dUe/dx > 0

Question 3 ప్రశ్న 3

Which combination correctly represents an adverse pressure gradient in an incompressible external stream?

A dp/dx > 0 and dUe/dx < 0 B dp/dx < 0 and dUe/dx > 0 C dp/dx = 0 and dUe/dx > 0 D dp/dx < 0 and dUe/dx < 0

Question 4 ప్రశ్న 4

For steady incompressible inviscid flow immediately outside a boundary layer, which relation connects pressure gradient and external velocity Ue?

A dp/dx = rho(dUe/dx) B dp/dx = rho Ue² C dp/dx = mu(dUe/dx) D dp/dx = -rho Ue(dUe/dx)

Question 5 ప్రశ్న 5

For a Newtonian fluid adjacent to a stationary wall, how is the local wall shear stress related to the boundary-layer velocity profile?

A tau_w = rho Ue² B tau_w = mu(du/dy)_wall C tau_w = mu(du/dx)_wall D tau_w = -dp/dx for every flow

Question 6 ప్రశ్న 6

Under the classical steady two-dimensional boundary-layer description, what condition identifies the incipient separation point?

A u at the wall becomes equal to Ue B The external velocity must become zero C tau_w = 0, equivalently (du/dy)_wall = 0 for a Newtonian fluid D The pressure gradient must become zero

Question 7 ప్రశ్న 7

What is indicated when the streamwise wall shear stress becomes negative downstream of a separation point under the usual positive-downstream sign convention?

A Near-wall flow reversal has developed B The boundary layer has become inviscid C The external pressure gradient must be favourable D The no-slip condition has been violated

Question 8 ప్రశ్న 8

For the classical steady two-dimensional laminar boundary-layer equation at a stationary impermeable wall, what does an adverse pressure gradient dp/dx > 0 imply for the wall-normal curvature of the streamwise velocity profile?

A (d²u/dy²)_wall must be negative because viscosity is positive B (d²u/dy²)_wall must be zero C No relation exists between the two quantities D (d²u/dy²)_wall is positive because mu(d²u/dy²)_wall = dp/dx

Question 9 ప్రశ్న 9

What is the usual effect of a favourable pressure gradient on an attached boundary layer?

A It necessarily causes immediate reverse flow B It accelerates the external flow and generally makes separation less likely C It forces the wall shear stress to become zero D It always creates a large separated wake

Question 10 ప్రశ్న 10

Which statement about an adverse pressure gradient is most accurate?

A Any positive dp/dx causes immediate separation at that exact point B It can occur only in laminar flow C It tends to promote separation, but a sufficiently weak adverse gradient can still permit attached flow D It always increases the near-wall streamwise momentum

Question 11 ప్రశ్న 11

Why is a turbulent boundary layer generally more resistant to separation than a laminar boundary layer under a comparable adverse pressure gradient?

A Turbulent mixing transports higher-momentum fluid toward the wall, producing a fuller mean velocity profile B A turbulent boundary layer has zero wall friction C Turbulence removes the adverse pressure gradient D Turbulent flow does not satisfy the no-slip condition

Question 12 ప్రశ్న 12

What is a common flow-field consequence after boundary-layer separation from a bluff or strongly curved body?

A Complete elimination of vortical motion B Immediate restoration of uniform inviscid flow at the wall C Zero pressure drag D Formation of a separated wake containing recirculation and strong velocity deficits

Question 13 ప్రశ్న 13

How does extensive boundary-layer separation commonly affect the drag of a bluff body?

A It eliminates pressure differences between the front and rear of the body B It commonly increases pressure or form drag by producing a low-pressure wake C It guarantees zero total drag D It affects only skin friction and cannot affect pressure drag

Question 14 ప్రశ్న 14

Why can streamlining a body help delay boundary-layer separation?

A It removes viscosity from the fluid B It forces the wall velocity to equal the free-stream velocity C It can make the downstream pressure recovery more gradual and reduce the severity of the adverse pressure gradient D It guarantees turbulent flow everywhere

Question 15 ప్రశ్న 15

How can boundary-layer suction through a porous surface delay separation?

A It removes low-momentum fluid from the near-wall region and produces a thinner, more energetic attached layer B It increases the amount of stagnant fluid next to the wall C It necessarily creates an adverse pressure gradient D It makes viscosity equal to zero

Question 16 ప్రశ్న 16

What is the principal purpose of vortex generators used for separation control?

A To eliminate all turbulent motion from the boundary layer B To reduce the external velocity to zero C To make the pressure constant everywhere D To mix higher-momentum outer fluid into the near-wall region and thereby energize the boundary layer

Question 17 ప్రశ్న 17

Which statement best describes deliberately triggering an earlier transition to turbulence as a possible separation-control strategy?

A It always reduces both pressure drag and skin-friction drag B It can delay separation because a turbulent boundary layer is more resistant to adverse pressure gradients, but it may increase skin-friction drag C It prevents all wake formation under every condition D It works by eliminating wall shear stress

Question 18 ప్రశ్న 18

Water of density 1000 kg/m³ has an external boundary-layer-edge velocity Ue = 4.0 m/s that is increasing at dUe/dx = +0.50 s^-1. What is dp/dx approximately?

A +8000 Pa/m B +2000 Pa/m C -2000 Pa/m D -8000 Pa/m

Question 19 ప్రశ్న 19

Air of density 1.2 kg/m³ has an external velocity Ue = 5.0 m/s that decreases at dUe/dx = -0.40 s^-1. What is the streamwise pressure gradient?

A +2.4 Pa/m B -2.4 Pa/m C +6.0 Pa/m D -6.0 Pa/m

Question 20 ప్రశ్న 20

Oil has dynamic viscosity mu = 1.0 × 10^-3 Pa·s. If the streamwise velocity gradient at a wall is (du/dy)_wall = 200 s^-1, what is the wall shear stress?

A 0.002 Pa B 0.020 Pa C 2.00 Pa D 0.200 Pa

Question 21 ప్రశ్న 21

In water of density 1000 kg/m³, the external velocity at a location is Ue = 2.0 m/s and the measured pressure gradient is dp/dx = +500 Pa/m. Using the incompressible external-flow relation, what is dUe/dx?

A +0.25 s^-1 B -0.25 s^-1 C +4.0 s^-1 D -4.0 s^-1

Question 22 ప్రశ్న 22

Along a surface, the static pressure rises from 100 kPa to 103 kPa over a downstream distance of 2.0 m. If the variation is approximated as linear, what is the average pressure gradient and its classification?

A -1500 Pa/m, favourable B +3000 Pa/m, favourable C +1500 Pa/m, adverse D -3000 Pa/m, adverse

Question 23 ప్రశ్న 23

For flow over a smoothly curved body, why is boundary-layer separation often associated with the downstream region after the external velocity has passed a maximum?

A The external stream then usually decelerates and experiences pressure recovery, producing an adverse pressure gradient B The external stream necessarily accelerates indefinitely C Pressure must decrease continuously after the velocity maximum D Wall shear must become zero at the velocity maximum itself

Question 24 ప్రశ్న 24

Which statement correctly distinguishes the no-slip condition from the separation criterion at a stationary solid wall?

A At separation, u at the wall suddenly becomes equal to the external velocity B Before separation, the fluid velocity at the wall is nonzero C The no-slip condition is invalid once an adverse pressure gradient begins D The wall velocity remains u = 0, while incipient separation is identified by (du/dy)_wall = 0

Question 25 ప్రశ్న 25

Consider the following statements about boundary-layer separation: I. A favourable pressure gradient corresponds to external-flow acceleration. II. An adverse pressure gradient tends to decelerate the external flow and can promote separation. III. At classical incipient separation, wall shear stress becomes zero. IV. Separation can produce a wake and substantially increase pressure drag. Which option is correct?

A I and II only B I, II and III only C II, III and IV only D I, II, III and IV

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