AEROSPIKE NOZZLESANAD S S ROLL NO: 50

MECHANICAL ENGINEERING

EARLY DEVELOPMENTStudies performed in Germany in conjunction with the development of the turbojet engine.NASA and the United States Air Force spent $500 million on the development of aerospike engines during the 1950s, 1960s, and 1970s.Similar work underway in West Germany from 1965 to the early 1970s. Aerospike

Engines used on the Messerschmitt Me 262.

CURRENT DEVELOPMENTLinear Aerospike SR-71 Experiment (LASRE) began at the NASA Dryden Flight Research Center in 1997.

Mounting 10% scale half-model on SR-71 Blackbird high-speed research aircraft.

Close-up view of the LASRE test engine mounted on the SR-71

Flight test of the LASRE aerospike engine mounted on the SR-71Used to measure the net thrust, plume expansion, plume aerodynamics, and other parameters of the engine. Tests performed from Mach 0.6 at 15,000 ft to Mach 3.2 at 80,000 feet to measure the altitude compensation characteristics of the design. Basic research on aerospike engines undertaken in Germany, France, and Japan.

ROCKET NOZZLE

Component of a rocket or air-breathing engine that produces thrust

Thermal energy to kinetic energy and directed it along nozzle's axis

Propellant = liquid hydrogen (H 2) + liquid oxygen (O 2)

Propellant pumped into combustion chamber and the fuel and oxidizer are mixed and burned

Exhaust gases pushed into the throat region of nozzle

Gases compressed due to less cross-sectional area of throat.

Nozzle itself gradually increases in cross-sectional area allowing the gases to expand.

Gases pushed against the walls of the nozzle creating thrust.

TYPES OF NOZZLE

Three types of nozzles :CONICAL NOZZLE :Simple and easy to construct.Small angle produces greater thrust DISADVANTAGES: longer and heavier nozzle is more

complex to build. large angles reduce performance at

low altitude

BELL NOZZLE:Bell consists of two sections.

Near the throat, the nozzle diverges at a relatively large angle but the degree of divergence tapers off further downstream. Near the nozzle exit, the divergence angle is very small.

The final bell shape will only be the optimum at one particular altitude.

Annular NozzlesThe term "annular" refers to the fact that combustion occurs along a ring, or annulus, around the base of the nozzle.

"Plug" refers to the centerbody that blocks the flow which is center portion of traditional nozzle.

Example – AEROSPIKE ENGINE

PRINCIPLE Basic concept of engine nozzle - efficiently expand the flow of exhaust gases from the rocket engine into one direction.

Bell Nozzle :Low altitudes - exhaust pressure low

Higher atmospheric pressure pushes the exhaust inward

Inequality causes exhaust to separate from the nozzle walls reducing amount of thrust generated

This is known as OVEREXPANSION

High altitude - exhaust pressure higher than ambient pressure causing the exhaust to expand past nozzle exit

Additional expansion occurs outside the nozzle

Expansion does not exert thrust on the nozzle -thrust lost

This is known as UNDEREXPANSION

Overexpansion and underexpansion reduce overall engine efficiency and thrust

Minimize the exit area at launch and increase it as the rocket ascends helps optimize the nozzle for each altitude and maximize the thrust

Such a nozzle, would markedly improve overall performance

Ideal nozzle would continually adjust its contour area ratio, and length to maximize thrust at each altitude - a concept known as altitude compensation.

Aerospike:Instead of firing exhaust out of a small hole in the middle of a bell, it avoids this random distribution by firing along the outside edge of a wedge-shaped protrusion - "spike"

Spike forms one side of a virtual bell, with the other side being formed by the outside air—thus "AEROSPIKE"

Plug centerbody forces exhaust gas flow to remain attached to the nozzle walls increasing the thrust efficiency of the nozzle

Aerospike has no outer walls Pressure of the atmosphere, or the outer free jet boundary, controls the pressure of the exhaust on the centerbody.

At high pressure - sea level – high ambient pressure forces exhaust to remain close to centerbody

Gases are more tightly focusedHence maximum efficiency and thrustAt low pressure - high altitudes - the gases will expand farther due to low atmospheric pressure

AEROSPIKE AERODYNAMICS

The nozzle generates thrust in three ways:1.THRUSTERSThrusters in chamber ,generate thrust as the fuel is combusted and exhausted

2. CENTERBODY Nozzles generate thrust when the

exhaust gases expand against the nozzle wall.

The exhaust gases in a spike nozzle expand against the spike centerbody rather than outer walls.

3.BASE"aerodynamic spike" is created

through the addition of a secondary circulating flow

Supersonic primary flow, consisting of the high-pressure gases exhausted from the thrusters, expands downstream of the base, the primary flow interacts with the subsonic, secondary flow causing it to circulate.

This low-pressure flow then re-circulates upward to exert an additional thrust force on the base.

AEROSPIKE FLOWFIELD

ADVANTAGES1. Smaller nozzle

2. Superior performance3. Less risk of failure4. Lower vehicle drag

5.Thrust vectoring

6. Lower vehicle weight

DISADVANTAGES1.Cooling2.Manufacturing

It can be concluded that aerospike engine is a solution to the loses in efficiency and thrust forces caused in other nozzles.

Cost of production is more, in long run it helps in the reduction of fuel loss and also significantly decreases the size.

The risk of failure as well is less, hence aerospike engine is an effective solution.

CONCLUSION

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