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Document search results: "pressure gradient"
 
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Title          
 Modeling and Simulation of Mixing Layer Flows...  
 
Abstract    

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
 
   
   

 

Title          
 Laminar Separation Bubble  
 
Abstract    

This essay focuses on the phenomenon of Laminar Separation Bubble observed at Low Reynolds Numbers. The effect of this bubble on the airfoil characteristics is discussed. Airfoils used at low Reynolds numbers have to be designed taking into consideration the finite space and time occupied by the bubble. Active as well as passive mechanisms to control/delay the formation of the bubble are also mentioned.

For conventional aircraft wings, whose Reynolds number exceeds a million, the flow is typically turbulent with the boundary layer able to strengthen itself by ‘mixing’. Consequently flow doesn’t separate until high angles of attack are encountered. For lower Reynolds numbers, the flow is initially laminar and is prone to separate even under mild adverse pressure gradient. Under certain flow conditions, the separated flow reattaches and forms a Laminar Separation Bubble (Fig. 1) while transitioning from laminar to turbulent state. Laminar separation bubble could modify the effective shape of the airfoil and consequently influence the aerodynamic performance, generally in a negative manner.

The need to understand low Reynolds number (104 to 106) aerodynamics is driven by variety of applicat...

 
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Added By - anandsaxena
Subject - Aeronautics and Astronautics
Document Type - White Paper
 
   
   

 

Title          
 The Role of Density Gradient in Liquid Rocket...  
 
Abstract    

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
 
   
   

 

Title          
 Experimental Study of Compressible Pipe Flow ...  
 
Abstract    

Anna Ekblom Johan Gullman-Strand's (KTH Sweeden) work on compressible pipe flow with friction and heat addition. The aim of the presented work was to compare existing theoretical analysis with experimental results in the feld of compressible pipe ow in a straight circular pipe with constant cross section area subjected to wall friction and heat addition. The equations describing pipe ow subjected to friction have been rederived. Two different models have been compared. The experiments were conducted on four pipes differing in length and friction factor.Quantities such as total inlet pressure, total inlet temperature, static pressure distribution along the pipe, venturi nozzle pressure difference, power added, outlet dynamic pressure distribution and outlet total temperature have been measured in order to determine the dependence on heat addition and friction. There was no apparent effect of heating on the flow eld though the input power was entirely transfered to the ow. The inuence of friction seems to have the predicted effect, since the achieved outlet Mach numbers were similar for all four pipes for similar input conditions. Inn contrast to the theoretical model of one-dimensional ow, the outlet Ma...

 
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Added By - autocrawler
Subject - Mechanical Engineering
Document Type - MS Thesis
 
   
   

 

Title          
 Fiber-Optic based Dynamic Pressure sensor for...  
 
Abstract    

Acquiring accurate, transient measurements in harsh environments has always pushed the limits of available measurement technology. Until recently, the technology to directly measure certain properties in extremely high temperature environments has not existed. Advancements in optical measurement technology have led to the development of measurement techniques for pressure, temperature, acceleration, skin friction, etc. using extrinsic Fabry-Perot interferometry (EFPI). The basic operating principle behind EFPI enables the development of sensors that can operate in the harsh conditions associated with turbine engines, high-speed combustors, and other aerospace propulsion applications where the flow environment is dominated by high frequency pressure and temperature variations caused by combustion instabilities, blade-row interactions, and unsteady aerodynamic phenomena. Using micromachining technology, these sensors are quite small and therefore ideal for applications where restricted space or minimal measurement interference is a consideration. In order to help demonstrate the general functionality of this measurement technology, sensors and signal processing electronics currently under development by Luna Innovations were used to...

 
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Added By - ajayvs
Subject - Mechanical Engineering
Document Type - Term Paper
 
   
   

 

Title          
 Rayleigh criteria and Combustion Instability  
 
Abstract    

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
 
   
   

 

Title          
 Adaptive Equalization Techniques using Recurs...  
 
Abstract    

In this project, we extend the use of methods of least squares to find a recursive algorithm solution of adaptive transversal filter. Given the LS solution at any time instant n-1, we find the solution at time n recursively using past solution and newly arrived data. This algorithm is known as Recursive Least Squares (RLS) algorithm. We show the convergence rate of RLS algorithm is faster than LMS algorithm by comparing the learning curves of two algorithms for specified channel response.

 
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Added By - ravigarg
Subject - Electrical Engineering
Document Type - White Paper
 
   
   

 

Title          
 Complex Classification Using Advanced Machine...  
 
Abstract    

In this report, we studied different complex classification models such as Gradient Descent, Multiclass Classification. We also used different Machine Learning tools such as LibSVM, MEGAm, and FastDT to design a complex classifier based on OVA and AVA approaches. We also designed 2 different Rank classifier using MEGAm library and evaluated its performance on the OHSUMED database. The binary classification accuracy (0-1) error using 20 different queries and 10 retrieved documents for each query was 33% for Ranking Classifier 1. The binary classification accuracy for Ranking Classifier 2 was 37%. However, the average ranking performance, as evaluated using DCG metric, was roughly 8% better for Ranking Classifier 2 as compared with Ranking Classifier 1. This improvement comes from the cost function used to penalize the mis-ranking.

 
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Added By - ravigarg
Subject - Computer Science
Document Type - Term Paper
 
   
   

 

Title          
 Combustion Instability in Liquid Rocket Engin...  
 
Abstract    

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
 
   
   

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