Transcript Inlets and Nozzles - Baylor University || School of

Inlets and Nozzles:
Design Considerations
EGR 4347
Analysis and Design of Propulsion
Systems
Subsonic Inlets:
Major Design Variables/Choices
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Inlet total pressure ratio and drag at cruise
Engine location on wing or fuselage
Aircraft attitude envelope
Inlet total pressure ratio and distortion envelope
Engine out windmilling airflow and drag
Integration of diffuser and fan flow path contour
Integration of external nacelle contour with thrust
reverser or accessories
• Flow field interaction with nacelle, pylon or wing
• Noise suppression requirements
Inlet Considerations
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Proximity to Ground - FOD
Proximity to nose gear - FOD
Proximity to Gun and Missile Bays - Smoke
Boundary layer buildup / diverter / stealth
Hide compressor face - stealth
Engine running during combat turn - access
Vortex ingestion - strake wakes
Subsonic Inlets
Subsonic Inlets
Subsonic Inlets:
Total Pressure Ratio
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mi  i
Tti
Pti
i 
; i 
; mci 
Tref
Pref
i
Subsonic Inlets:
Typical Airflow Requirements
Subsonic Inlets:
Total Pressure Distortion
Subsonic Inlets:
Drag
Subsonic Inlets:
Diffusers
Subsonic Inlets:
Boundary Layer Control
Inlet Integration
• Keep ducts as short as possible
– reduces volume, reduces viscous losses
– limits on turning flow without separation
• Keep offset ducts long enough to prevent
separation
• Use the wing and fuselage to shield the
inlet, reduce distortion
• Watch proximity to ground
Nozzle Design Considerations
• Accelerate the flow to high velocity with minimum
total pressure loss
• Match exit and atmospheric pressures as closely as
desired
• Permit afterburner operation without affecting main
engine operation – requires variable-area nozzle
• Allow for cooling of walls if necessary
• Mix core and bypass streams of turbofan if necessary
• Allow for thrust reversing if desired
• Suppress jet noise and infrared radiation (IR) if
desired
• Thrust vector control if desired
Nozzle Geometry
Gross Thrust Coefficient
C
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fg
Fg actual
Fg ideal
• Exhaust velocity
vector angularity
• Friction in the
boundary layers
• Loss of massflow –
leakage in nozzle
• Flow
nonuniformities
Nozzle Integration
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Smooth boat tails (e.g., F-18)
Minimize interference between ...
– Nozzle and control surfaces
– Nozzle and nozzle
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Pay attention to rotation geometry
Evaluate trades
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2-D or round (axi) nozzles?
integrated into trailing edge?
shielded above? below? from the side?
thrust vectoring? reversing?