# lectures-intro-propulsion - 650:460 Aerodynamics...

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650:460 AerodynamicsIntroduction to PropulsionProf. Doyle KnightTel: 848 445 4464, Email: [email protected]Office hours: Tues and Thur, 4:30 pm - 6:00 pm and by appointmentFall 20121
IntroductionAfterburning turbojet engine2
IntroductionConservation of massX˙min=X˙moutThusρoVoA+ ˙ms+ ˙mf= ( ˙mo+ ˙mf) +ρoVo(A9-A)Note definition ofρo, ˙ms, ˙mo,A. The above equation simplifies to˙ms= ˙mo-ρoVoA93
IntroductionConservation of momentumX˙mVx|out-X˙mVx|in=XFxThe net force isXFx=F|thrust|{z}F-(p9-po)A9The momentum fluxes areX˙mVx|out=( ˙mo+ ˙mf)V9+ρoV2o(A-A9)X˙mVx|in=ρoV2oA+ ˙msVo4
IntroductionConservation of momentumThe equation simplifies to( ˙mo+ ˙mf)V9-˙moVo=F-(p9-po)A9DefineF=Funinstalled= ( ˙mo+ ˙mf)V9-˙moVo+ (p9-po)A9andDram= ˙moVoFor subsonic flow at exit,p9=po.For supersonic flow at exit,p9is not necessarily equal topo.p9<po: overexpandedp9=po: perfectly expandedp9.po: underexpanded5
IntroductionConservation of momentumDefinegross thrustFg= ( ˙mo+ ˙mf)V9+ (p9-po)A9and thusF=Fg-DramFor multiple exhaustsF=XFg|nozzles-Dram|inletsFor turbofanF= ˙m9V9+ ˙m19V19+ (p9-po)A9+ (p19-po)A19-˙moVo6
IntroductionTakeoff thrustAt takeoff, the air speedVois small and thusF|takeoff( ˙mo+ ˙mf)V9+ (p9-po)A97
Installed ThrustTheinstalled thrustis the actual measured thrust when the engine isinstalled on the pylonTheuninstalled thrustis the thrust that would be measured if theengine were isolated from the wing and pylonThe uninstalled and installed thrust are related byF|installed=F|uninstalled-D|nacelleThe text shows that a different choice of control volume yields thesame result for uninstalled thrust8
IntroductionTheinstalled net thrustaccounts for the effects of the engineinstallation on the pylon9

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