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Propulsion Integration (Engine intakes (functions
decelerate flow
incr…
Propulsion Integration
-
Engine intakes
functions
- decelerate flow
- incr flow P
- avoid shocks/separated flow
- minimise total energy loss (ie maximise total P recovery)
intake nomenclature
- mass flow rate MFR: freestream area/highlight area
- highlight: stagnation point
- throat: narrowest part
at high speed/cruise:
- MFR<1 (free stream area is smaller than highlight area so flow EXPANDS towards highlight
- supervel OUTSIDE the intake (possible separation)
- near supersonic sp, a blunt nose leads to more drag so sharp nose is better for high sp!
- also note: the faster u fly, the longer the cowling shd be so that the vel grad is more gentle (u dont want flow separation!)
at low speeds
- MFR>1 (freestream area larger than highlight area)
- supervel INSIDE intake (ie near the throat)
- throat M shd be capped <0.8 to prevent exponential decr in P recovery (this is when shocks form and flow is choked at throat)
- NOTE: another cause of total P loss is separation at lip aka lip loss
- you would want a larger contraction ratio cos that would make the lip blunter
- but if u wanna fly fast, u need a sharper lip
HOW?
use blow-in doors to prevent flow separation
inlet installation
- shorter lower lip than upper lip to "tip" the inlet at a slight -ve aoa because of the upwash from the wing
- this also decr the cowl drag
OEI flight
- OEI means low sp, high aoa and possibly high sideslip angle
- theres additional D due to large rudder def
- wind milling/blocked rotor D
- incr forebody D
SO, cowling design has to minimise the extra D of the failed engine
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