lecture6 - MECH 6251/498D Rocket Fundamentals So far, we...

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MECH 6251/498D
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Rocket Fundamentals • So far, we have used the conservation of momentum for a ideal rocket model to determine how a rocket engine generates thrust for a given effective exhaust velocity • Then we solved the momentum equation for a moving rocket vehicle to determine how overall mission parameters such as Δ v are related to propellant mass, structural mass, etc. • Orbital Mechanics This lecture we will look more closely at the rocket engine itself, to determine how the engine achieves such a high exhaust velocity
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Rocket Fundamentals We have identified the specific impulse as a very important characteristic of a rocket propulsion system, we have to ask ourselves: • How do we control the specific impulse? • Which components of a rocket propulsion system will affect the specific impulse? • How do we analyze and design these components, which will allows us the control over the specific impulse?
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Idealized Rocket Design Technical Objectives: • Review of basic nozzle theory (Mathematical background) • Define the parameters C* (characteristic velocity) and thrust coefficient C F and explain how they are measured • Show that C* is a function only of energetic propellant performance and thrust coefficient is a function only of the nozzle performance. Relate C* and C F to I sp , effective exhaust velocity and thrust.
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What is a Nozzle? • Function of rocket nozzle is to convert thermal energy in propellants into kinetic energy as efficiently as possible • Nozzle is substantial part of the total engine mass • Many of the historical data suggest that 50% of solid rocket failures stemmed from nozzle problems The design of the nozzle must trade off: 1. Nozzle size (needed to get better performance) against nozzle weight penalty 2. Complexity of the shape for shock-free performance vs. cost of fabrication • Mechanical Structure for carrying thrust load • Thrust vector control
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Main Component of a LRE Nozzle
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Nozzle Technology Advanced concepts with altitude adaptation Classical type
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Nozzle Types (Brief Overview) The subsonic portion of the nozzle is quite insensitive to shape – the subsonic portion of the acceleration remains isentropic. The divergent nozzle is where the decisions come into play. Conical Nozzle: easier to manufacture – for small thrusters Divergence losses: exit velocity is not all in the desired direction. Bell Nozzle: complex shape highest efficiency (nearly axial flow at exhaust) large base drag during atmospheric flight after burnout Plug nozzle or Aerospike nozzle (linear or annular) Altitude compensating Expansion-Deflection Nozzle (E-D) shortest nozzle of the “enclosed” types.
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Idealized Nozzle Design Consider the following idealized rocket engine nozzle: Basic Analysis • Expansion in the nozzle is modeled as quasi one-dimensional flow .
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This note was uploaded on 12/12/2010 for the course MECH 351 taught by Professor Chekhov during the Fall '10 term at Concordia Canada.

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lecture6 - MECH 6251/498D Rocket Fundamentals So far, we...

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