Aircraft Propulsion Systems

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Aircraft Propulsion Systems

Aircraft Propulsion Systems

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  • 1. Review AE430 Aircraft Propulsion Systems Gustaaf Jacobs
  • 2. Note
    • Bring Anderson to exam for tables.
  • 3. Goals
    • Understand and analyze gas turbine engines:
      • Turbojet
      • Turbofan (turbojet + fanned propeller)!
      • Ramjet
  • 4. Analysis
    • Analysis
      • Energy control volume per engine component
        • Pressure and temperature changes for ideal engine
        • With efficiency definitions: pressure and temperature changes for non-ideal engine
      • Control Volume over complete engine:
        • Momentum balance=> thrust, propulsion efficiency
        • Energy balance or thermo analysis:
          • Brayton cycle: Thermal efficiency
  • 5. Analysis
    • Detailed component analysis
      • Inlets
        • Subsonic flow analysis in 1D
          • Pressure recovery estimate
        • Shock analysis in 1D inlet (converging-diverging)
          • Estimate of losses
          • External deceleration principles
        • 2D shock external deceleration
          • Oblique shock analysis
          • Estimate spillage and losses
  • 6. Analysis
    • Combustor
      • Qualitative idea of combustion physics
        • Fuel-air ratio (stoichiometric)
        • Flame speed
        • Flame holding
      • Quantitative: pressure loss with 1D channel flow analysis + heat addition=> not treated due to time restrictions
    • Compressor/Turbine
      • Estimate of pressure, temperature recovery with momentum and energy balance
      • Velocity triangles analysis: first order estimate of compressor aerodynamics
  • 7. Control Volume Analysis: Basic Idea T
  • 8. Engine Performance Parameters
    • Propulsion efficiency, ratio thrust power to add kinetic energy
    • Thermal efficiency, ratio added kinetic energy to total energy consumption
    • Total efficiency
    • Thrust Specific Fuel Consumption
  • 9. Thermodynamic cycles
    • Diagram that looks at the change of state variables at various stage of the engine
    • Ideal gas turbine: Brayton cycle
    • Isentropic compression, constant p heat addition, constant p heat rejection
    • First law of thermodynamics analysis gives expression for η th
  • 10. Ideal Ramjet
    • Analyze each stage using thermodynamic analysis with energy balance and isentropic relations to find:
      • P, T, p 0 , T 0
      • v e , T/m a
      • f
  • 11. Ideal Ramjet
    • p t,0 =p t,7 , p 0 =p 7 => M 0 =M 7
    • T 7 > T 0 since heat is added during combustion, so v 7 >v 0 => Thrust
    • Fuel to air ratio, use first law:
  • 12.
    • Non-isentropic compression and expansion: losses lead to lowered total pressure and temperature
    • Define total pressure ratios before and after components to quantify the efficiency:
      • r c , r n ,r d
    Non-ideal ramjet
  • 13.
    • Major difference with ramjet p total is not constant like in ramjet but increases and decrease in compressor and turbine.
    • To find these ratios work from front to back through each stage
    • Specific: compressor and turbine power are the same so (first law)
    Non-Ideal turbojet
  • 14. Definition of component efficiencies
    • E.g. diffuser
    • Relates actual total temperature increase to an isentropic temperature increase
    • The isentropic temperature can be related to the total pressure using isentropic relations
    • The total pressure distribution is determined from front to back.
    • Each stage has an effiiciency like this.
  • 15. Turbofan
    • Example on blackboard.
  • 16. Detailed analysis of components
  • 17. Intakes
    • Convert kinetic energy to pressure
    • Subsonic
      • External acceleration or decelleration depends on intake design and speed of aircraft
      • High speed: spillage. Low speed: stall.
      • Diffuser design: prevent stall: use computational (XFOIL, MSES) and experimental validation to design
  • 18. Supersonic intake
    • 1D: converging-diverging nozzle
    • Ideal: isentropic decelleration supersonic to throat, subsonic after throat
    • Not possible in practice
    • Shocks in nozzle
    • Possible design: shock close to throat and M~1 at throat
    • Need overspeeding to swallow shock in throat.
    • Kantrowitz-Donaldson: design condition is shock swallowing condition.
  • 19. Supersonic diffuser
    • 2-D nozzle
      • Use multiple oblique shocks to slow flow down with small losses in total pressure
      • Use oblique shock analysis
  • 20. Combustor + Compressor
    • Discussed in last classes
  • 21.  
  • 22.