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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
Introduction•Afterburning turbojet engine2
Introduction•Conservation 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
Introduction•Conservation 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
Introduction•Conservation 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
Introduction•Takeoff thrustAt takeoff, the air speedVois small and thusF|takeoff≈( ˙mo+ ˙mf)V9+ (p9-po)A97
Installed Thrust•Theinstalled thrustis the actual measured thrust when the engine isinstalled on the pylon•Theuninstalled thrustis the thrust that would be measured if theengine were isolated from the wing and pylon•The uninstalled and installed thrust are related byF|installed=F|uninstalled-D|nacelle•The text shows that a different choice of control volume yields thesame result for uninstalled thrust8
Introduction•Theinstalled net thrustaccounts for the effects of the engineinstallation on the pylon9
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Term
Spring
Professor
Knight
Tags
Force, Momentum, WI, performance parameters, mo vo, ms Vo