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Inlets and Nozzles: Design Considerations

Inlets and Nozzles: Design Considerations. EGR 4347 Analysis 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

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Inlets and Nozzles: Design Considerations

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  1. Inlets and Nozzles:Design Considerations EGR 4347 Analysis and Design of Propulsion Systems

  2. 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

  3. 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

  4. Subsonic Inlets

  5. Subsonic Inlets

  6. Subsonic Inlets: Total Pressure Ratio

  7. Subsonic Inlets: Typical Airflow Requirements

  8. Subsonic Inlets: Total Pressure Distortion

  9. Subsonic Inlets: Drag

  10. Subsonic Inlets: Diffusers

  11. Subsonic Inlets: Boundary Layer Control

  12. 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

  13. 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

  14. Nozzle Geometry

  15. Gross Thrust Coefficient • Exhaust velocity vector angularity • Friction in the boundary layers • Loss of massflow – leakage in nozzle • Flow nonuniformities

  16. 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?

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