Aircraft Propulsion Systems

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Aircraft Propulsion Systems

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Aircraft Propulsion Systems

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

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