components-inlet Flashcards
what is the main potential problems with a diffuser (inlet) lip at low mach numbers (take off)
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.
what is the main potential problems with a diffuser (inlet) lip at high mach numbers (cruise)
a large lip will lead to acceleration on the outside which can become supersonic and lead to losses and shock
in a normal shock, which values increase, decrease, and stay the same
increase:
- static temperature
- static enthalpy
- static pressure
- entropy
- density
decrease:
- mach number
- air speed
- total pressure
same:
- total temp
- total enthalpy
what are some of the most important results about normal shocks
- 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
when do normal and oblique shocks occur?
normal: supersonic to subsonic or vise versa
oblique: at contours with wedges
how do values increase and decrease with oblique shock?
same as normal
increase:
- static temperature
- static enthalpy
- static pressure
- entropy
- density
decrease:
- mach number
- air speed
- total pressure
same:
- total temp
- total enthalpy
in an oblique shock, what angle is the streamline deflected?
wedge angle
(not the shock angle)
what is the differences in the oblique shock gas parameter relations
the oblique shock equations only include the component of Ma normal to velocity (otherwise they are identical)
what happens at a wedge angle of zero?
a normal shock (the strong shock option)
how can supersonic inlets be classified? (3 ways)
of shocks
- single
- multiple
internal vs external
- internal
- external
- mixed
geometry
- 2d (wedge)
- axial symetry (conical)
why do you want all external oblique shocks to end up at the same point on the lip
to capture the maximum mass flow
explain ideal internal compression
convergent and divergent portion of nozzle
- mach number decreases to sonic and minimum throat area
- divergent part continues slowing it down via continuity
what is the starting problem for full internal compression?
-there will be a normal shock upstream of the inlet so engine will never get to design mach
why is there a gap between the diffuser and the fuselage
so the boundary layer of the fuselage is not sucked into the engine
which has lower total pressure loses, internal or external compression
external
how are oblique external shockes typically combined
several weak oblique shocks and one normal shock in the throat
what are the disadvantages of external compression inlet
- 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
how does mixed compression work?
-several oblique shocks (external and internal) and a final normal shock at the diffuser throat
why does the variable throat area inlet come about?
even with the mixed type, there is still a starting problem because the normal shock should occur at the diffuser throat.
what are the two types of spillage in offdesign conditions for a mixed compression inlet
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.
