lectures-intro-propulsion - 650:460 Aerodynamics Introduction to Propulsion Prof Doyle Knight Tel 848 445 4464 Email [email protected] Oce hours

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

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650:460 Aerodynamics Introduction to Propulsion Prof. Doyle Knight Tel: 848 445 4464, Email: [email protected] Office hours: Tues and Thur, 4:30 pm - 6:00 pm and by appointment Fall 2012 1
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Introduction Afterburning turbojet engine 2
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Introduction Conservation of mass X ˙ m in = X ˙ m out Thus ρ o V o A + ˙ m s + ˙ m f = ( ˙ m o + ˙ m f ) + ρ o V o ( A 9 - A ) Note definition of ρ o , ˙ m s , ˙ m o , A . The above equation simplifies to ˙ m s = ˙ m o - ρ o V o A 9 3
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Introduction Conservation of momentum X ˙ mV x | out - X ˙ mV x | in = X F x The net force is X F x = F | thrust | {z } F - ( p 9 - p o ) A 9 The momentum fluxes are X ˙ mV x | out = ( ˙ m o + ˙ m f ) V 9 + ρ o V 2 o ( A - A 9 ) X ˙ mV x | in = ρ o V 2 o A + ˙ m s V o 4
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Introduction Conservation of momentum The equation simplifies to ( ˙ m o + ˙ m f ) V 9 - ˙ m o V o = F - ( p 9 - p o ) A 9 Define F = F uninstalled = ( ˙ m o + ˙ m f ) V 9 - ˙ m o V o + ( p 9 - p o ) A 9 and D ram = ˙ m o V o For subsonic flow at exit, p 9 = p o . For supersonic flow at exit, p 9 is not necessarily equal to p o . p 9 < p o : overexpanded p 9 = p o : perfectly expanded p 9 . p o : underexpanded 5
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Introduction Conservation of momentum Define gross thrust F g = ( ˙ m o + ˙ m f ) V 9 + ( p 9 - p o ) A 9 and thus F = F g - D ram For multiple exhausts F = X F g | nozzles - D ram | inlets For turbofan F = ˙ m 9 V 9 + ˙ m 19 V 19 + ( p 9 - p o ) A 9 + ( p 19 - p o ) A 19 - ˙ m o V o 6
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Introduction Takeoff thrust At takeoff, the air speed V o is small and thus F | takeoff ( ˙ m o + ˙ m f ) V 9 + ( p 9 - p o ) A 9 7
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Installed Thrust The installed thrust is the actual measured thrust when the engine is installed on the pylon The uninstalled thrust is the thrust that would be measured if the engine were isolated from the wing and pylon The uninstalled and installed thrust are related by F | installed = F | uninstalled - D | nacelle The text shows that a different choice of control volume yields the same result for uninstalled thrust 8
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Introduction The installed net thrust accounts for the effects of the engine installation on the pylon 9
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  • Spring '09
  • Knight
  • Force, Momentum, WI, performance parameters, mo vo, ms Vo

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