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Unit 2: Inlets - Practice Quiz

ASE202 — Propulsion-I 60 Questions
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1 What is inlet stall in a subsonic inlet?

Internal flow and stall in subsonic inlets Easy
A. A complete absence of boundary-layer growth
B. A uniform increase in total pressure
C. A steady region of uniformly accelerated flow
D. A large region of separated and unsteady flow

2 Which condition most commonly promotes stall in a subsonic inlet diffuser?

Internal flow and stall in subsonic inlets Easy
A. A strong adverse pressure gradient
B. A uniform upstream temperature
C. A constant ambient pressure
D. A small favorable pressure gradient

3 Boundary layer separation occurs when the near-wall flow does what?

Boundary layer separation Easy
A. Accelerates to a uniform velocity
B. Maintains constant momentum everywhere
C. Reaches the local speed of sound
D. Slows down and begins to reverse

4 Which diffuser design change generally helps prevent boundary layer separation?

Boundary layer separation Easy
A. Increasing the surface roughness
B. Increasing the wall divergence angle
C. Adding a sudden area expansion
D. Reducing the wall divergence angle

5 What is inlet spillage in the external flow near a subsonic inlet?

Major features of external flow near a subsonic inlet Easy
A. Fuel flowing backward through the inlet duct
B. Exhaust gas entering the compressor face
C. Air flowing around rather than into the inlet
D. Air leaking through the diffuser wall

6 Why is a rounded inlet lip useful during subsonic operation?

Major features of external flow near a subsonic inlet Easy
A. It helps the flow remain attached
B. It eliminates all pressure losses
C. It blocks the captured streamtube
D. It creates a strong normal shock

7 For incompressible flow, if is the capture area and is the minimum inlet area, which relation follows from continuity?

Relation between minimum area ratio and eternal deceleration ratio Easy
A.
B.
C.
D.

8 Under the constant-density approximation, what happens to when the external deceleration ratio increases?

Relation between minimum area ratio and eternal deceleration ratio Easy
A. It decreases
B. It increases
C. It remains fixed
D. It becomes zero

9 Which quantity is commonly used to evaluate inlet diffuser performance?

Diffuser performance Easy
A. Total pressure recovery
B. Fuel heating value
C. Turbine blade speed
D. Exhaust nozzle thrust

10 What is the main purpose of a subsonic diffuser?

Diffuser performance Easy
A. Decrease velocity and decrease static pressure
B. Increase velocity and decrease static pressure
C. Increase velocity and increase total pressure
D. Decrease velocity and increase static pressure

11 What is the primary function of shocks in a supersonic inlet?

Supersonic inlets Easy
A. Keep the airflow fully incompressible
B. Expand and accelerate the airflow
C. Compress and decelerate the airflow
D. Remove all inlet pressure losses

12 For supersonic upstream flow, the flow immediately downstream of a normal shock is normally:

Supersonic inlets Easy
A. Subsonic
B. Supersonic
C. Stationary
D. Incompressible

13 What does it mean for a supersonic inlet to be started?

Starting problem on supersonic inlets Easy
A. The external airflow has become stationary
B. The inlet lip has reached sonic speed
C. The inlet has swallowed its starting shock
D. The engine has begun receiving fuel

14 Which feature commonly indicates an unstarted supersonic inlet?

Starting problem on supersonic inlets Easy
A. A complete recovery of inlet total pressure
B. A shock-free flow at every operating point
C. A uniform supersonic flow through the diffuser
D. A normal shock standing ahead of the inlet

15 Which area change generally helps a supersonic inlet swallow its starting shock?

Shock swallowing by area variation Easy
A. Decreasing the throat area
B. Increasing the throat area
C. Closing the capture area
D. Blocking the diffuser exit

16 Why may a variable-geometry inlet enlarge its throat during starting?

Shock swallowing by area variation Easy
A. To increase the effective contraction ratio
B. To reduce the effective contraction ratio
C. To reverse the external airflow
D. To eliminate the inlet mass flow

17 Where does external deceleration occur in an external-compression supersonic inlet?

External declaration Easy
A. Ahead of the inlet entrance
B. Behind the exhaust nozzle
C. Within the turbine rotor
D. Inside the combustion chamber

18 Which flow feature commonly produces external deceleration for a supersonic inlet?

External declaration Easy
A. Oblique shock waves
B. Fuel spray patterns
C. Exhaust expansion fans
D. Turbine wake vortices

19 In the critical operating model of a supersonic inlet, where is the terminal normal shock ideally positioned?

Models of inlet operation Easy
A. At the inlet lip
B. Far ahead of the inlet
C. Behind the turbine
D. At the nozzle exit

20 Which description best matches subcritical operation of a supersonic inlet?

Models of inlet operation Easy
A. The normal shock is ahead of the inlet
B. The normal shock is deep inside the diffuser
C. The normal shock is absent from the flow
D. The normal shock is behind the nozzle

21 A subsonic inlet diffuser is redesigned with a larger divergence angle while its length and inlet conditions remain unchanged. What is the most likely consequence?

Internal flow and stall in subsonic inlets Medium
A. Earlier flow separation and lower pressure recovery
B. Later flow separation and higher pressure recovery
C. Lower wall pressure and unchanged flow uniformity
D. Higher exit Mach number and lower diffusion

22 Which observation most directly indicates that a subsonic inlet has entered a stalled operating condition?

Internal flow and stall in subsonic inlets Medium
A. A gradual reduction in external spillage only
B. Large pressure fluctuations and distorted exit flow
C. Uniform velocity with a lower inlet temperature
D. A steady increase in exit total pressure

23 A diffuser contains a thick, low-momentum boundary layer near its wall. Which modification is most effective for delaying separation?

Boundary layer separation Medium
A. Raising the downstream back pressure substantially
B. Polishing the wall while retaining the same adverse pressure gradient and diffuser geometry
C. Increasing the diffuser angle without changing its length
D. Removing low-momentum air through boundary-layer bleed

24 Why can vortex generators delay boundary-layer separation in an inlet diffuser?

Boundary layer separation Medium
A. They convert all turbulent flow into laminar flow
B. They reduce the core-flow total temperature
C. They eliminate the adverse pressure gradient completely
D. They transfer high-momentum fluid toward the wall

25 A subsonic inlet captures less mass flow than the amount approaching its geometric capture area. What external-flow feature should be expected?

Major features of external flow near a subsonic inlet Medium
A. Choked flow across the capture plane
B. A normal shock ahead of the inlet
C. Complete stagnation of the entire approaching stream
D. Flow spillage around the inlet lip

26 During high mass-flow operation, strong acceleration around a rounded subsonic-inlet lip primarily produces which local condition?

Major features of external flow near a subsonic inlet Medium
A. Reduced static pressure near the lip
B. Increased total pressure near the lip
C. A detached normal shock extending across the complete inlet entrance
D. Uniform stagnation pressure throughout the boundary layer

27 For incompressible external deceleration, the velocity at the inlet plane is . Using continuity, what is the required ratio of inlet area to upstream capture area ?

Relation between minimum area ratio and eternal deceleration ratio Medium
A.
B.
C.
D.

28 During external deceleration, and . What area ratio follows from steady continuity?

Relation between minimum area ratio and eternal deceleration ratio Medium
A.
B.
C.
D.

29 An inlet has an upstream total pressure of and a diffuser-exit total pressure of . What is its total-pressure recovery?

Diffuser performance Medium
A.
B.
C.
D.

30 Which quantity is most suitable for evaluating how effectively a subsonic diffuser converts kinetic energy into static pressure?

Diffuser performance Medium
A. Exit static pressure divided by inlet temperature
B. Wall shear stress relative to ambient pressure
C. Mass-flow rate multiplied by the diffuser length
D. Static-pressure rise relative to the ideal rise

31 Why do efficient supersonic inlets generally use several oblique shocks before a terminal normal shock?

Supersonic inlets Medium
A. They eliminate shock-wave and boundary-layer interactions under every operating condition
B. They increase Mach number before entering the diffuser
C. They reduce Mach number with less total-pressure loss
D. They keep static pressure constant through compression

32 In a mixed-compression supersonic inlet operating near its design condition, where does compression occur?

Supersonic inlets Medium
A. Both outside and inside the inlet
B. Only downstream of the engine face
C. Entirely through friction in a constant-area duct
D. Only ahead of the inlet lip

33 What is meant by an unstarted supersonic inlet?

Starting problem on supersonic inlets Medium
A. All shocks are swallowed and remain internally stable
B. A strong shock remains ahead of or near the entrance
C. The inlet delivers uniform supersonic flow directly to the combustor
D. The throat operates isentropically at every back pressure

34 Which change can help a fixed-flight-condition supersonic inlet transition from an unstarted to a started state?

Starting problem on supersonic inlets Medium
A. Increasing back pressure downstream of the inlet
B. Increasing downstream pressure until a stronger detached normal shock forms ahead of the cowl
C. Blocking boundary-layer bleed passages
D. Reducing back pressure downstream of the inlet

35 How is variable throat area commonly used to start a supersonic inlet?

Shock swallowing by area variation Medium
A. Enlarge the throat to swallow the shock, then reduce it
B. Hold the throat fixed while increasing wall friction throughout the internal duct
C. Close the throat fully and reopen it after stagnation
D. Reduce the throat until the shock moves upstream

36 An inlet contraction is too severe to swallow its normal shock at the current Mach number. Which geometric adjustment directly improves its starting capability?

Shock swallowing by area variation Medium
A. Increase the minimum flow area
B. Increase contraction while keeping the throat fixed
C. Decrease the minimum flow area
D. Extend the constant-area section without changing either the capture area or throat area

37 What is a likely penalty of obtaining substantial inlet deceleration outside the cowl at an off-design mass-flow condition?

External declaration Medium
A. Increased spillage drag
B. Elimination of wave drag
C. Perfect total-pressure recovery
D. A constant capture streamtube independent of engine demand

38 Shifting more supersonic compression from inside the inlet to external compression generally has which design effect?

External declaration Medium
A. It removes all off-design shock motion
B. It guarantees zero spillage at low mass flow
C. It reduces the required internal compression
D. It makes the downstream flow supersonic without any total-pressure loss or wave interaction

39 An inlet model defines mass-flow ratio as actual captured mass flow divided by the geometric capture mass flow. If the ratio is , what fraction of the geometric capture flow is spilled?

Models of inlet operation Medium
A.
B.
C.
D.

40 Which feedback mechanism is essential in a dynamic model of supersonic-inlet buzz?

Models of inlet operation Medium
A. Steady wall temperature coupled only with material density
B. Atmospheric humidity coupled with an otherwise perfectly steady inviscid compression field
C. Constant shock position coupled with fixed mass flow
D. Shock motion coupled with separation and mass-flow changes

41 At a fixed flight condition, a subsonic inlet is throttled to a substantially lower corrected mass flow. Which coupled mechanism most directly promotes internal inlet stall?

Internal flow and stall in subsonic inlets Hard
A. Higher mass flux reduces the boundary-layer momentum, causing separation near the diffuser exit
B. Higher back pressure strengthens the adverse pressure gradient, causing separation and increased compressor-face distortion
C. Lower back pressure accelerates the diffuser flow, causing choking and uniform compressor-face pressure
D. Lower static pressure suppresses diffusion, causing an isentropic normal shock near the inlet lip

42 Two axisymmetric subsonic diffusers have the same inlet area and terminal area ratio. Diffuser X is short with rapid initial expansion, whereas diffuser Y is longer with staged expansion. Why can Y have a larger stall margin despite greater wetted area?

Internal flow and stall in subsonic inlets Hard
A. Its larger wetted area raises wall shear, eliminating displacement thickness throughout the diffuser
B. Its staged expansion maintains constant static pressure, preventing all boundary-layer growth
C. Its smaller local diffusion angles limit adverse gradients, outweighing its additional skin-friction loss
D. Its longer passage makes the flow incompressible, eliminating adverse pressure gradients near the wall

43 Which condition most precisely identifies the onset of steady boundary-layer separation on an inlet wall?

Boundary layer separation Hard
A. The local external velocity reaches the acoustic speed at the wall
B. The wall shear stress reaches zero before becoming negative downstream
C. The streamwise pressure gradient first becomes positive at the wall
D. The displacement thickness becomes equal to the local duct radius

44 A localized shock-induced separation forms near the throat of a high-speed inlet. If only a small amount of boundary-layer bleed is available, where is it generally most effective?

Boundary layer separation Hard
A. Immediately upstream of the shock interaction, where low-momentum wall fluid can be removed
B. On the external cowl afterbody, where bleed directly increases the internal throat area
C. Far downstream of the shock interaction, where the separated shear layer has fully mixed
D. At the capture-plane centerline, where total pressure is highest and wall shear is absent

45 For a subsonic inlet whose capture streamtube area is smaller than its geometric highlight area, which external-flow state is expected?

Major features of external flow near a subsonic inlet Hard
A. All highlight flow enters the duct, while an internal sonic line controls the captured mass flow
B. A detached normal shock forms ahead of the lip, producing a subsonic terminal compression
C. The approaching streamtube contracts toward the lip, producing zero spillage and negative drag
D. Excess approaching flow spills around the lip, producing streamline curvature and additive drag

46 An inlet operating in crosswind develops strong circumferential total-pressure distortion even though its area-averaged recovery changes little. Which external-flow change best explains this result?

Major features of external flow near a subsonic inlet Hard
A. The freestream total pressure varies azimuthally before interacting with the inlet streamtube
B. The entire external boundary layer separates simultaneously at one axial cowl location
C. The capture streamtube remains axisymmetric while static pressure decreases uniformly around the lip
D. The stagnation line shifts and lip acceleration becomes azimuthally nonuniform around the inlet

47 A capture streamtube of area decelerates externally before reaching a highlight of area . If and , what area ratio follows from continuity?

Relation between minimum area ratio and eternal deceleration ratio Hard
A.
B.
C.
D.

48 An inlet must provide at least an external velocity reduction, so . If compression limits to at most , what is the minimum feasible under one-dimensional continuity?

Relation between minimum area ratio and eternal deceleration ratio Hard
A.
B.
C.
D.

49 An incompressible diffuser has . Its measured pressure-recovery coefficient is . What is its diffuser effectiveness relative to ideal pressure recovery?

Diffuser performance Hard
A.
B.
C.
D.

50 At a compressor face, of the mass flow has , while the remaining has . Using mass-flow weighting, what is the overall total-pressure recovery?

Diffuser performance Hard
A.
B.
C.
D.

51 Why does a mixed-compression supersonic inlet generally use several oblique shocks before a terminal normal shock rather than one normal shock at the flight Mach number?

Supersonic inlets Hard
A. Multiple shocks preserve total pressure exactly because entropy changes cancel between successive shocks
B. Staged oblique compression increases terminal-shock Mach number and prevents boundary-layer growth
C. Multiple shocks remove the need for a subsonic diffuser downstream of the terminal shock
D. Staged oblique compression lowers terminal-shock Mach number and reduces total-pressure loss

52 For a calorically perfect gas with , a normal shock stands in a uniform stream at . Which pair most closely gives the downstream Mach number and total-pressure ratio?

Supersonic inlets Hard
A. and
B. and
C. and
D. and

53 For and , a normal shock at the inlet entrance gives and . According to the Kantrowitz starting condition, approximately what minimum throat-to-entrance area ratio is required?

Starting problem on supersonic inlets Hard
A.
B.
C.
D.

54 A fixed-geometry inlet exceeds the Kantrowitz contraction limit and remains unstarted despite a reduction in downstream back pressure. Which modification most directly enables starting?

Starting problem on supersonic inlets Hard
A. Increase internal contraction while holding the capture area and terminal shock fixed
B. Temporarily enlarge the throat or provide bypass flow until the normal shock is swallowed
C. Increase downstream back pressure until the subsonic region reaches the inlet entrance
D. Temporarily reduce the throat area so the external normal shock moves into the diffuser

55 Which variable-geometry sequence is most appropriate for starting a high-contraction supersonic inlet and then restoring its design compression?

Shock swallowing by area variation Hard
A. Open the throat for shock swallowing, then reduce it gradually after stable internal operation
B. Close the throat for shock swallowing, then enlarge it abruptly after external unstart
C. Reduce both throat and bypass areas during swallowing, then increase external contraction
D. Hold the throat fixed during swallowing, then close the capture area ahead of the shock

56 A disturbance drives the terminal shock upstream toward the lip of an otherwise started variable-geometry inlet. What immediate control action best opposes an unstart?

Shock swallowing by area variation Hard
A. Reduce bypass flow to decrease capacity and stabilize the shock near the lip
B. Increase effective throat area to raise swallowed mass flow and draw the shock downstream
C. Increase diffuser back pressure to strengthen the shock and move it downstream
D. Decrease effective throat area to raise back pressure and draw the shock downstream

57 Increasing external supersonic deceleration through additional oblique compression can improve terminal-shock recovery, but what competing effect can eliminate the expected benefit?

External declaration Hard
A. Higher external pressure can preserve total pressure while eliminating all cowl wave drag
B. Reduced pre-shock Mach number can increase normal-shock entropy beyond its high-Mach value
C. Weaker pressure gradients can cause choking, uniformity, and additional static-pressure recovery
D. Stronger shock-boundary-layer interactions can cause separation, distortion, and additional total-pressure loss

58 Which observation most clearly indicates that a supersonic inlet has transitioned from started operation to an externally decelerated unstarted state?

External declaration Hard
A. Oblique shocks converge at the design cowl location with a uniform compressor-face profile
B. A terminal shock remains downstream of the throat with reduced spillage and stable recovery
C. A normal shock stands ahead of the lip with increased spillage, drag, and pressure oscillation
D. The throat remains supersonic while downstream back pressure and additive drag both decrease

59 A quasi-steady inlet map predicts the mean operating point accurately but cannot reproduce inlet buzz. What minimum modeling extension is needed to represent the instability?

Models of inlet operation Hard
A. Add only a constant total-pressure loss to the steady inlet characteristic
B. Remove downstream pressure dynamics and prescribe a fixed normal-shock location
C. Add downstream volume compliance and duct-flow inertance to the inlet characteristic
D. Replace compressible continuity with an incompressible algebraic mass-flow relation

60 In a lumped inlet-plenum model, is proportional to . At an equilibrium, which local condition indicates static stability to a small plenum-pressure perturbation?

Models of inlet operation Hard
A.
B.
C.
D.
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