Inlets and Nozzles: Design Considerations
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Transcript of Inlets and Nozzles: Design Considerations
Inlets and Nozzles:Design Considerations
EGR 4347Analysis and Design of Propulsion
Systems
Subsonic Inlets:Major Design Variables/Choices• 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
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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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
• Exhaust velocity vector angularity
• Friction in the boundary layers
• Loss of massflow – leakage in nozzle
• Flow nonuniformities
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Nozzle Integration• Smooth boat tails (e.g., F-18)• Minimize interference between ...
– Nozzle and control surfaces– Nozzle and nozzle
• Pay attention to rotation geometry• Evaluate trades
– 2-D or round (axi) nozzles?– integrated into trailing edge?– shielded above? below? from the side?– thrust vectoring? reversing?