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 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


 Laminar Separation Bubble  

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


 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


 Hints for understanding low speed wind tunnel...  

The effort here has been to compile and present collectively the concepts of Low Speed Wind Tunnel. I have tried to make it explanatory with help of large number of figures and pictures whose sources have been mentioned under them. I have tried to incorporate as much latest information as available via Internet although the backbone of the work is ‘Wind Tunnel Technique’ by R.C. Pankhurst, National Physical Laboratory, Teddington, England. It includes a very descriptive documentation of the Wind Tunnel and in a very organized manner.This work was done as an assignment for one of the undergrad courses. Information may not be very current but the general principles remain the same nevertheless.

Wind tunnel testing is the technical support of any major development process involving aerodynamics. It is used for aircraft, helicopters,cars, trains, and laboratory research.It is estimated that it took the Wright Brothers less than 20 hours of wind tunnel testing to produce their successful Flyer (although their empirical research was a life time achievement). The Douglas DC-3, perhaps the most successful commercial aircraft ever built, required about 100 hours of wind tunnel testing. Wind tunnel time has been steadi...

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

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