components-inlet

Question 1

what is the main potential problems with a diffuser (inlet) lip at low mach numbers (take off)

Answer 1

flow separation on the innerside of the lip. The stagnation point is closer to the outside so it has farther to go and less speed.

Question 2

what is the main potential problems with a diffuser (inlet) lip at high mach numbers (cruise)

Answer 2

a large lip will lead to acceleration on the outside which can become supersonic and lead to losses and shock

Question 3

in a normal shock, which values increase, decrease, and stay the same

Answer 3

increase:
- static temperature
- static enthalpy
- static pressure
- entropy
- density

decrease:
- mach number
- air speed
- total pressure

same:
- total temp
- total enthalpy

Question 4

what are some of the most important results about normal shocks

Answer 4

• can have large total pressure loss (high mach number) which represent flow loss
• limited loss near mach one (really want to design so they happen here)
• effective at increasing static pressure

Question 5

when do normal and oblique shocks occur?

Answer 5

normal: supersonic to subsonic or vise versa
oblique: at contours with wedges

Question 6

how do values increase and decrease with oblique shock?

Answer 6

same as normal

increase:
- static temperature
- static enthalpy
- static pressure
- entropy
- density

decrease:
- mach number
- air speed
- total pressure

same:
- total temp
- total enthalpy

Question 7

in an oblique shock, what angle is the streamline deflected?

Answer 7

wedge angle

(not the shock angle)

Question 8

what is the differences in the oblique shock gas parameter relations

Answer 8

the oblique shock equations only include the component of Ma normal to velocity (otherwise they are identical)

Question 9

what happens at a wedge angle of zero?

Answer 9

a normal shock (the strong shock option)

Question 10

how can supersonic inlets be classified? (3 ways)

Answer 10

of shocks

• single
• multiple

internal vs external

• internal
• external
• mixed

geometry

• 2d (wedge)
• axial symetry (conical)

Question 11

why do you want all external oblique shocks to end up at the same point on the lip

Answer 11

to capture the maximum mass flow

Question 12

explain ideal internal compression

Answer 12

convergent and divergent portion of nozzle

• mach number decreases to sonic and minimum throat area
• divergent part continues slowing it down via continuity

Question 13

what is the starting problem for full internal compression?

Answer 13

-there will be a normal shock upstream of the inlet so engine will never get to design mach

Question 14

why is there a gap between the diffuser and the fuselage

Answer 14

so the boundary layer of the fuselage is not sucked into the engine

Question 15

which has lower total pressure loses, internal or external compression

Answer 15

external

Question 16

how are oblique external shockes typically combined

Answer 16

several weak oblique shocks and one normal shock in the throat

Question 17

what are the disadvantages of external compression inlet

Answer 17

• large flow turning will lead to need for large flow turning in the subsonic portion (can lead to flow separation)
• lip shock makes high drag
• high angle of lip requires high flow turning which can again lead to flow separation

Question 18

how does mixed compression work?

Answer 18

-several oblique shocks (external and internal) and a final normal shock at the diffuser throat

Question 19

why does the variable throat area inlet come about?

Answer 19

even with the mixed type, there is still a starting problem because the normal shock should occur at the diffuser throat.

Question 20

what are the two types of spillage in offdesign conditions for a mixed compression inlet

Answer 20

supersonic spillage –> oblique shock not attatched to lip (still IS to wedge) so there is spillage

subsonic spillage –> shock detached from wedge and is normal shock.