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 Rayleigh criteria and Combustion Instability  

A short literature review on Rayleigh's Criteria is provided. This criteria is widely used in mechanical and aerospace engineering areas to understand the phenomena of combustion instability. In continuously running combustion systems where combustion occurs inside a volume of relatively low losses, small amplitude pressure disturbance and small amplitude heat release fluctuations can couple with each other in a positive feedback loop leading to very large amplitude pressure oscillations often ending up in limit cycle oscillations. Such oscillations are detrimental to the combustion system (power or propulsion) for it exposes the system to large mechanical fatigue, thermal loads and can lead to catastrophic failures.

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


 A report discussing critical factors affectin...  

Various researches have tried to determine the factors that are responsible for a successful project. The purpose of this paper is to explore the critical factors affecting project performance and develop a framework for measuring success of construction projects. In this paper, a set of key performance indicators (KPIs), namely planning and control, procurement, time, cost, quality and environmental performance are identified as crucial to project performance amongst many others. The importance and the limitations of the suggested KPIs are discussed. The validity of the proposed KPIs is also tested by three case studies. Recommended solutions targeting each area of concern from lessons learnt in the case studies provide a basis for improved project management for large scale projects. With the development of KPIs, a benchmark for measuring the performance of a construction project can be set.

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Added By - Arpita Ghosh
Subject - Architecture
Document Type - Assignment


 Sustainable Energy Production and Utilization...  

A comprehensive development plan has been generated for creating a sustainable community in a remote location as part of a graduate research project. Southeast Tucson, in the state of Arizona, is the region of interest. The community is designed using the Leadership in Energy and Environmental Design (LEED) for Neighborhood Development standards as a guideline.

The Leadership in Energy and Environmental Design (LEED) Green Building Rating System, developed by the U.S. Green Building Council (USGBC), provides a suite of standards for environmentally sustainable construction. Since its inception in 1998, LEED has grown to encompass more than 14,000 projects in the United States and 30 countries covering 1.062 billion square feet (99 km˛) of development area.The hallmark of LEED is that it is an open and transparent process where the technical criteria proposed by the LEED committees are publicly reviewed for approval by the more than 10,000 membership organizations that currently constitute the USGBC. Individuals recognized for their knowledge of the LEED rating system are permitted to use the LEED Accredited Professional (AP) acronym after their name, indicating they have passed the accreditation exam given by the...

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Added By - sidpatel
Subject - Energy
Document Type - White Paper


 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 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

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