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 Combustion Instability in Liquid Rocket Engin...  

Work on liquid rocket engine combustion instabilities began in the early 1940s (Culick and Yang 1995). One of the most critical concepts in liquid rocket combustion instability, that of time lag (as a coordinating factor in influencing organized oscillations in liquid rocket combustion chambers) originated around this time in von Kármán‟s group at the Jet Propulsion Laboratory around 1941 (cf. Summerfield 1951) shortly after oscillations were observed in early tests in liquid rocket engines in the United States. The essential idea was that there existed a finite time delay when an element of propellant entered the combustor and when heat was released from it. This delay controlled the phasing between heat release and pressure oscillations thereby making the system stable or unstable as per Rayleigh‟s criteria. In the years that followed, this model was applied to various studies involving combustion instability in liquid rocket engines. Gunder and Friant (1950), Yachter (1951) and Summerfield (1951) analyzed low frequency chugging instability arising from the interaction between feed system and combustion process using a constant time lag model. Crocco (1951;1952) introduced the time varying combustion time lag and use...

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Added By - A Ghosh
Subject - Aeronautics and Astronautics
Document Type - Literature Review


 The Combustion of Aluminum in Solid Rocket Pr...  

The trophy piece of technology in any modern rocket system is without question the liquid bi-propellant engine. Despite their sophistication, power, and precision the workhorse responsible for launching men and machines into space is based on solid rocket technology more than 700 years old. The earliest historical use of gunpowder dates back to the 300 B.C where in modern day China bamboo tubes filed with gunpowder were thrown into fires during celebrations, the noise warding away evil spirits. 500 years later in 1232 A.D at the battle of Kai-fung-fu the Chinese military used the first recorded rockets against the invading Mongol Horde. As the Mongols moved through china, they took emerging technologies with them and by 1241 A.D, the rocket had made it to the battlefields of Europe. By 1300 A.D, arsenals around Europe had some rocket technology, based entirely on the use of gunpowder for propulsive motive. A lack of control over rocket trajectories hindered much development by western militaries, who also found the tendency of a misguided missile to start a fire counterproductive. In the Eighteenth century, work had begun on developing a more powerful propellant, and although some progress had been made the independent work of Rob...

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Added By - ajayvs
Subject - Aeronautics and Astronautics
Document Type - Term Paper


 The Role of Density Gradient in Liquid Rocket...  

Experimental and analytical studies were conducted to investigate key physical mechanisms responsible for flame-acoustic coupling during the onset of acoustically driven combustion instabilities in liquid rocket engines (LREs). Controlled experiments were conducted in which a turbulent hydrogen-oxygen (GH2-GO2) diffusion flame, established downstream of a two-dimensional model shear coaxial injector was acoustically forced by a compression driver unit mounted in a transverse direction and excited through a broad range of frequencies (200Hz-2000Hz) and amplitudes. Characteristic interactions between flame and acoustics visualized through OH* and CH* chemiluminescence imaging and dynamic pressure measurements obtained using high frequency dynamic pressure transducers indicated that small acoustic disturbances could be amplified by flame-acoustic coupling under certain conditions leading to substantial modulation in spatial heat release fluctuations. Density gradient between fuel and oxidizer was found to significantly affect the way acoustic waves interacted with density stratified flame fronts. The particular case of an asymmetric flame front oscillation under transverse acoustic forcing indicated that baroclinic vorticity, generat...

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Added By - A Ghosh
Subject - Aeronautics and Astronautics
Document Type - PhD Thesis


 Modeling and Simulation of Mixing Layer Flows...  

Film cooling has been selected for the thermal protection of the composite nozzle extension of the J-2X engine which is currently being developed for the second stage of NASA’s next generation launch vehicle, the Ares I rocket. However,several challenges remain in order to achieve effective film cooling of the nozzle extension and to ensure its safe operation. The extreme complexity of the flow (three-dimensionalwakes, lateral flows, vorticity, and flow separation) makes predicting film cooling performance difficult. There is also a dearth of useful supersonic film cooling data available for engineers to use in engine design and a lack of maturity of CFD tools to quantitatively match supersonic film cooling data. This dissertation advances the state of the art in film cooling by presenting semi-empirical analytical models which improve the basic physical understanding and prediction of the effects of pressure gradients, compressibility and density gradients on film cooling effectiveness. These models are shown to correlate most experimental data well and to resolve several conflicts in the open literature. The core-to-coolant stream velocity ratio, R, and the Kays acceleration parameter, KP, are identified as the critical paramete...

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Added By - kdellimo
Subject - Aeronautics and Astronautics
Document Type - PhD Thesis

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