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Review AE430 Aircraft Propulsion Systems Gustaaf Jacobs

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Note Bring Anderson to exam for tables.

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Goals Understand and analyze gas turbine engines: Turbojet Turbojet Turbofan (turbojet + fanned propeller)! Turbofan (turbojet + fanned propeller)! Ramjet Ramjet

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Analysis Analysis Energy control volume per engine component Energy control volume per engine component Pressure and temperature changes for ideal enginePressure and temperature changes for ideal engine With efficiency definitions: pressure and temperature changes for non-ideal engineWith efficiency definitions: pressure and temperature changes for non-ideal engine Control Volume over complete engine: Control Volume over complete engine: Momentum balance=> thrust, propulsion efficiencyMomentum balance=> thrust, propulsion efficiency Energy balance or thermo analysis:Energy balance or thermo analysis: Brayton cycle: Thermal efficiency Brayton cycle: Thermal efficiency

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Analysis Detailed component analysis Inlets Inlets Subsonic flow analysis in 1DSubsonic flow analysis in 1D Pressure recovery estimate Pressure recovery estimate Shock analysis in 1D inlet (converging-diverging)Shock analysis in 1D inlet (converging-diverging) Estimate of losses Estimate of losses External deceleration principles External deceleration principles 2D shock external deceleration2D shock external deceleration Oblique shock analysis Oblique shock analysis Estimate spillage and losses Estimate spillage and losses

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Analysis Combustor Qualitative idea of combustion physics Qualitative idea of combustion physics Fuel-air ratio (stoichiometric)Fuel-air ratio (stoichiometric) Flame speedFlame speed Flame holdingFlame holding Quantitative: pressure loss with 1D channel flow analysis + heat addition=> not treated due to time restrictions 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 Estimate of pressure, temperature recovery with momentum and energy balance Velocity triangles analysis: first order estimate of compressor aerodynamics Velocity triangles analysis: first order estimate of compressor aerodynamics

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Control Volume Analysis: Basic Idea T

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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

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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

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Ideal Ramjet Analyze each stage using thermodynamic analysis with energy balance and isentropic relations to find: P, T, p 0, T 0 P, T, p 0, T 0 v e, T/m a v e, T/m a f f

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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:

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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 r c, r n,r d Non-ideal ramjet

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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

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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.

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Turbofan Example on blackboard.

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Detailed analysis of components

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Intakes Convert kinetic energy to pressure Subsonic External acceleration or decelleration depends on intake design and speed of aircraft External acceleration or decelleration depends on intake design and speed of aircraft High speed: spillage. Low speed: stall. High speed: spillage. Low speed: stall. Diffuser design: prevent stall: use computational (XFOIL, MSES) and experimental validation to design Diffuser design: prevent stall: use computational (XFOIL, MSES) and experimental validation to design

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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.

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Supersonic diffuser 2-D nozzle Use multiple oblique shocks to slow flow down with small losses in total pressure Use multiple oblique shocks to slow flow down with small losses in total pressure Use oblique shock analysis Use oblique shock analysis

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Combustor + Compressor Discussed in last classes

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