Nozzle Research Paper

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INTRODUCTION

The nozzle is a thrust producing component of a rocket or air-breathing engine. It helps in the conversion of the thermal energy into kinetic energy of the combustion engine and then direct it along the nozzle's axis.

The fuel and the oxidiser are injected into the combustion chamber at a mass flow rate, m ̇ where they are mixed and burned. The exhaust is then pushed along the nozzle. They compress to a high pressure near the throat and gradually expand as the cross-sectional area increases.During this expansion process,they push against the wall contour,thereby producing thrust force.
Mathematically, the ultimate purpose of the nozzle is to expand the gases as efficiently as possible so as to produce maximum
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m ̇ = mass flow rate. v_(exit ) = The exit exhaust velocity. p_exit = pressure at the exit of the nozzle. p_∞ = ambient pressure of the atmosphere.
A_exit = Area at the nozzle exit.

CLASSIFICATION OF NOZZLES

Conical Nozzle:
The walls of conical nozzle diverge at a constant angle.
ADVANTAGES
They are easy and simple to design. If the conical angle is small, it will maximize the axial component of the exit velocity. Therefore, more thrust will be produced. Specific impulse produced is high.

DISADVANTAGES: They are longer and heavier. Therefore, it is difficult to manufacture. In order to reduce the size, we can increase the divergent angle but it reduces the performance at low altitude, as it leads to flow separation and over-expansion.
Bell Nozzle:
It is called so because of it’s shape. There is divergence in the nozzle at two sections: Near the throat, where the divergence angle is relatively large. Further downstream, it tapers off. Near the nozzle exit, the divergence angle is very small.
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A nozzle in which the entire expansion occurs internally.

ADVANTAGES: SMALLER NOZZLE: For the same performance, truncated spike can be far smaller than a bell nozzle. ALTITUDE COMPENSATING is their primary advantage.

Size comparison of a bell and a plug nozzle for the same performance.

SUPERIOR PERFORMANCE MODULAR COMBUSTION CHAMBER: The aerospike engine is made up of small thrusters which are easy to develop and less expensive too.This gives greater versatility to the engine. LESS RISK OF FAILURE: It uses simple gas generator with low chamber pressure which reduces the risk of catastrophic explosion. Though the performance may reduce due to low chamber pressure,The high expansion ratio of aerospike makes up for this. LOWER VEHICLE WEIGHT: Though aerospike nozzles tend to be heavier than bell nozzle, it shares major structural elements with vehicle, thereby reducing the weight.

LOWER DRAG: The base portion is filled by aerospike nozzle, which reduces the base drag. Thereby, total drag is reduced. Illustration of aerospike nozzles installed on the X-33 [from Rocketdyne,

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