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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A Numerical and Experimental Investigation of High-Speed Liquid Jets - Their Characteristics and Dynamics.

Zakrzewski, Sam, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2002 (has links)
A comprehensive understanding of high-speed liquid jets is required for their introduction into engine and combustion applications. Their transient nature, short lifetime, unique characteristics and the inability to take many experimental readings, has inhibited this need. This study investigates the outflow of a high-speed liquid jet into quiescent atmospheric air. The key characteristics present are, a bow shock wave preceding the jet head, an enhanced mixing layer and the transient deformation of the liquid jet core. The outflow regime is studied in an experimental and numerical manner. In the experimental investigation, a high-speed liquid water jet is generated using the momentum exchange by impact method. The jet velocity is supersonic with respect to the impinged gaseous medium. The resulting jet speed is Mach 1.8. The jet is visualised with the use of shadowgraph apparatus. Visualisation takes place over a variety of time steps in the liquid jet???s life span and illustrates the four major development stages. The stages progress from initial rapid core jet expansion to jet stabilisation and characteristic uniform gradient formation. The visualisation shows that at all stages of the jet???s life it is axi-symmetric. One dimensional nozzle analysis and a clean bow shock wave indicate that the pulsing jet phenomenon can be ignored. In the numerical investigation, a time marching finite volume scheme is employed. The bow shock wave characteristics are studied with the use of a blunt body analogy. The jet at a specific time frame is considered a solid body. The jet shape is found to have an important influence on the shock position and shape. Analysis of the results indicates a shock stand-off similar to that seen in experimental observations and the prediction of shock data. The jet life span is modelled using a species dependent density model. The transient calculations reproduce the key jet shape characteristics shown in experimental visualisation. The mushrooming effect and large mixing layer are shown to develop. These effects are strongest when the shock wave transience has yet to stabilise. Quantitative analysis of the mixing layer at varying time steps is presented.
2

Numerical and experimental study of transient laminar natural convection of high prandtl number fluids in a cubical cavity

Younis Taha Elamin, Obai 23 November 2009 (has links)
NUMERICAL AND EXPERIMENTAL STUDY OF TRANSIENT LAMINAR NATURAL CONVECTION OF HIGH PRANDTL NUMBER FLUIDS IN A CUBICAL CAVITYObai Younis Taha ElaminLa convección natural en espacios cerrados, se encuentra ampliamente en sistemas naturales e industriales. El objetivo general de este trabajo es desarrollar y validar una herramienta de simulación capaz de predecir las tasas de enfriamiento de aceite en un tanque. Esta herramienta ha de tener en cuenta la variación de la viscosidad del aceite para dar información detallada de las tasas de enfriamiento del aceite bajo diferentes condiciones de contorno térmicas realisticas. En primer lugar, la influencia de diferentes condiciones de contorno térmicas en las paredes, la variación de la viscosidad y la conductividad de la pared en la convección natural del flujo laminar transitorio en una cavidad cúbica con seis paredes térmicamente activo están analizadas.Para analizar el efecto individual de las paredes laterales de la cavidad en el proceso de enfriamiento, la segunda parte de este estudio considera que, tanto numéricamente como experimentalmente, la transición de la convección natural laminar en una cavidad cúbica con dos paredes opuestas frías y verticales.Nuevas relaciones de escala que tengan en cuenta la variación de la viscosidad con la temperatura, no publicadas anteriormente en la literatura, se derivan de las velocidades de la capa límite, por el tiempo necesario para la capa límite para alcanzar el estado estacionario y para la velocidad y el espesor de las intrusiones horizontales.NUMERICAL AND EXPERIMENTAL STUDY OF TRANSIENT LAMINAR NATURAL CONVECTION OF HIGH PRANDTL NUMBER FLUIDS IN A CUBICAL CAVITYObai Younis Taha ElaminFree convection in enclosed spaces is found widely in natural and industrial systems. The general objective of this work is to develop and validate a simulation tool able to predict the cooling rates of oil in a tank. This tool has to take into account the variation of the oil viscosity to give detailed information of the cooling rates of the oil under different realistic thermal boundary conditions. First, the influence of different thermal wall boundary conditions, the variation of the viscosity and the wall conductivity on the transient laminar natural convection flow in a cubical cavity with the six walls thermally active is studied numerically. To analyze the individual effect of the side walls of the cavity on the cooling process, the second part of this study considers, numerically and experimentally, the transient laminar natural convection in a cubical cavity with two cold opposite vertical walls. The shadowgraph technique is employed to visualize the development of the transient convective flow. New scaling relations that take into account the viscosity variation with temperature, not reported previously in the literature, are derived for the boundary layer velocities, for the time needed for the boundary layer to reach the steady state and for the velocity and thickness of the horizontal intrusions.
3

Investigation of Effervescent Atomization Using Laser-Based Measurement Techniques

Ghaemi, Sina Unknown Date
No description available.
4

Investigation of Effervescent Atomization Using Laser-Based Measurement Techniques

Ghaemi, Sina 11 1900 (has links)
Effervescent atomization has been a topic of considerable investigation in the literature due to its important advantages over other atomization mechanisms. This work contributes to the development of both effervescent atomizers and also laser-based techniques for spray investigation In order to develop non-intrusive measurement techniques for spray applications, a procedure is suggested to characterize the shape of droplets using image-based droplet analyzers. Image discretization which is a major source of error in droplet shape measurement is evaluated using a simulation. The accuracy of StereoPIV system in conducting droplet velocity measurement in a spray field is also investigated. To assist in the design of effervescent atomizers, bubble formation during gas injection from a micro-tube into liquid cross-flow is investigated using a Shadow-PIV/PTV system. The generated spray fields of two effervescent atomizers which operate using a porous and a typical multi-hole air injector are compared using qualitative images and Shadow-PTV measurement.
5

A Numerical and Experimental Investigation of High-Speed Liquid Jets - Their Characteristics and Dynamics.

Zakrzewski, Sam, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2002 (has links)
A comprehensive understanding of high-speed liquid jets is required for their introduction into engine and combustion applications. Their transient nature, short lifetime, unique characteristics and the inability to take many experimental readings, has inhibited this need. This study investigates the outflow of a high-speed liquid jet into quiescent atmospheric air. The key characteristics present are, a bow shock wave preceding the jet head, an enhanced mixing layer and the transient deformation of the liquid jet core. The outflow regime is studied in an experimental and numerical manner. In the experimental investigation, a high-speed liquid water jet is generated using the momentum exchange by impact method. The jet velocity is supersonic with respect to the impinged gaseous medium. The resulting jet speed is Mach 1.8. The jet is visualised with the use of shadowgraph apparatus. Visualisation takes place over a variety of time steps in the liquid jet???s life span and illustrates the four major development stages. The stages progress from initial rapid core jet expansion to jet stabilisation and characteristic uniform gradient formation. The visualisation shows that at all stages of the jet???s life it is axi-symmetric. One dimensional nozzle analysis and a clean bow shock wave indicate that the pulsing jet phenomenon can be ignored. In the numerical investigation, a time marching finite volume scheme is employed. The bow shock wave characteristics are studied with the use of a blunt body analogy. The jet at a specific time frame is considered a solid body. The jet shape is found to have an important influence on the shock position and shape. Analysis of the results indicates a shock stand-off similar to that seen in experimental observations and the prediction of shock data. The jet life span is modelled using a species dependent density model. The transient calculations reproduce the key jet shape characteristics shown in experimental visualisation. The mushrooming effect and large mixing layer are shown to develop. These effects are strongest when the shock wave transience has yet to stabilise. Quantitative analysis of the mixing layer at varying time steps is presented.
6

On the influence of nozzle geometries on supersonic curved wall jets

Robertson Welsh, Bradley January 2017 (has links)
Circulation control involves tangentially blowing air around a rounded trailing edge in order to augment the lift of a wing. The advantages of this technique over conventional mechanical controls are reduced maintenance and lower observability. Despite the technology first being proposed in the 1960s and well-studied since, circulation control is not in widespread use today. This is largely due to the high mass flow requirements. Increasing the jet velocity increases both the efficiency (in terms of mass flow) and effectiveness. However, as the jet velocity exceeds the speed of sound, shock structures form which cause the jet to separate. Recent developments in the field of fluidic thrust vectoring (FTV) have shown that an asymmetrical convergent-divergent nozzle capable of producing an irrotational vortex (IV) has the potential to prevent separation through eliminating stream-wise pressure gradients. In this study, the feasibility of preventing separation at arbitrarily high jet velocities through the use of asymmetrical nozzle geometries designed to maintain irrotational (and stream-wise pressure gradient free) flow is explored. Furthermore, the usefulness of an adaptive nozzle geometry for the purpose of extending circulation control device efficiency and effectiveness is defined. Through a series of experiments, the flow physics of supersonic curved wall jets is characterised across a range of nozzle geometries. IV and equivalent area ratio symmetrical convergent-divergent nozzles are compared across three slot height to radius ratios (H/R): H/R = 0.1, H/R = 0.15, H/R = 0.2. The conclusion of this study is that at low H/R (0.1 and 0.15), there is no significant difference in behaviour between IV and symmetrical nozzles, whilst at high H/R (0.2), the IV nozzles begin separating whilst correctly expanded due to the propagation of pressure upstream from the edge of the reaction surface via the boundary layer. Consequently, it is shown that symmetrical nozzles of equivalent mass flow at high H/R have a higher separation NPR compared to IV nozzles. Specifically, the elimination of favourable, in addition to adverse stream-wise pressure gradients contradicts the expected behaviour of IV nozzles. The separation NPR for nozzles tested in this study, in addition to past studies is subsequently plotted against the throat height to radius ratios (A*/R). This shows that in fact, no previous experiments have shown a higher separation NPR for IV nozzles compared to symmetrical nozzles of equivalent mass flow. The overall outcome is that neither fixed geometry IV, nor adaptive nozzles are justified to maintain attachment, or to improve efficiency. This is because fixed nozzle geometries designed for higher separation NPR do not show any performance deficit when operating at lower NPRs. However, the throat height could be varied to maximise effectiveness (at the expense of mass flow). The contributions to new knowledge made by this study are as follows: the development of a new method of combining shadowgraph and schlieren images to simplify and enhance visualisation of supersonic flows; the use of pressure sensitive paint (PSP) to study the structure of the supersonic curved wall jet before and after separation; the identification of a clear mechanism for the separation of supersonic curved wall jets, valid over a broad range of nozzle geometries (including a clarification of previously unexplained behaviour witnessed in prior studies); the explanation that reattachment hysteresis occurs due to the upstream movement of the point of local separation at full separation (specifically, this explains why certain geometries such as backward-facing steps prevent reattachment hysteresis).
7

Effect of Corrugated Outer Wall On Operating Regimes of Rotating Detonation Combustors

Knight, Ethan 21 September 2018 (has links)
No description available.
8

AN EXPERIMENTAL AND COMPUTATIONAL STUDY OF PULSE DETONATION ENGINES

ALLGOOD, DANIEL CLAY January 2004 (has links)
No description available.
9

Characterization of Electrohydrodynamic (EHD) heat transfer enhancement mechanisms in melting of organic Phase Change Material (PCM)

Nakhla, David January 2018 (has links)
The effect of using high voltage DC and AC on the heat transfer process during the melting of a Phase Change Material (PCM) in a rectangular enclosure was studied experimentally and numerically. The experiments were conducted for two configurations: (a) a horizontal rectangular enclosure in which the initial melting process is governed by heat conduction, (b) a vertical rectangular enclosure in which the initial melting process is governed by heat convection. The level of heat transfer enhancement was quantified by using a novel experimental facility for the horizontal configuration. The experimental methodology was verified first against non-EHD melting cases and then was further expanded to include the EHD effects. The experiments showed that EHD forces can be used to enhance a conduction dominated melting up to a maximum of 8.6-fold locally and that the level of enhancement is directly related to the magnitude of the applied voltage. It was found that the main mechanism of enhancement in these cases can be attributed to the electrophoretic forces and that the role of the dielectrophoretic forces is minimal under the applied voltages. In the vertical configuration, the effect of the magnitude of the applied voltage, the applied voltage wave-form, the gravitational Rayleigh number, Stefan number and the aspect ratio of the enclosure on the heat transfer enhancement were investigated experimentally. A novel shadowgraph experimental measurement system was developed and verified against the analytical correlations of natural convection in rectangular enclosures and the non-EHD melting performance was verified against the bench mark experiments of Ho (1984). The shadowgraph system was used to measure the local heat transfer coefficient across the heat source wall (the heat exchanger surface). The local heat transfer measurements along with the melting temporal profiles were used to explain and visualize the coupling between the Electrohydrodynamics (EHD) forces and the gravitational forces. It was found that the EHD forces could still enhance the melting process even for an initially convection dominated melting process. The mechanism of enhancement was found to be a bifurcation of the initial convection cell into multiple electro-convective cells between the rows of the electrodes. The shadowgraph system was used to assess the interaction between the electrical and the gravitational forces through the visualization of these cells and quantifying their size. The EHD heat transfer enhancement factor was found to increase by the increase of the applied voltage, reaching a 1.7 fold enhancement at the lower gravitational Rayleigh number tested and 1.45 fold for the highest gravitational Rayleigh and Stefan number. The effect of the polarity of the applied voltage was tested for the different cases and it was found that there was no significant difference between the positive and the negative polarities when the magnitude of the applied voltage was below 4 kV. At higher voltages- 6kV- the negative polarities showed better level of enhancement when compared to the positive applied voltage. It was again found that the main mechanism of enhancement is attributed to charge injection from the high voltage electrodes. A scaling analysis was conducted based on the previous conclusions and the dominant mechanism of enhancement to describe the problem in non-dimensional form. An electrical Rayleigh number was introduced and its magnitude was correlated to the magnitude of the injected current. The melt volume fraction was then represented against the non-dimensional parameter (n+1)(H/W)Fo.Ste.RaE^0.25 and the melt fraction temporal profiles for the different voltages collapsed well against this parameter. Finally, a numerical analysis was conducted on the role of the dielectrophoretic forces during the melting of Octadecane and when they would become of significant importance. The results of the numerical model supported the experimental findings and suggested that a minimum of 15 kV is needed in order to realize the effect of the dielectrophoretic forces. The numerical model was used to understand the interaction between the gravitational and the dielectrophoretic forces at different ranges of both gravitational Rayleigh number and electrical Rayleigh number. The model was complemented with scaling analysis to determine the governing scales of the problem and the dielectrophoretic Rayleigh number was deduced from the study. / Thesis / Doctor of Philosophy (PhD)
10

Design and cold flow evaluation of a miniature Mach 4 Ramjet

Ferguson, Kevin M. 06 1900 (has links)
Approved for public release, distribution is unlimited / Methods used for designing the ramjet included conic shock tables; isentropic flow tables and the GASTURB code was used for aerothermodynamic performance prediction. The flow field through the proposed geometry was computed using the OVERFLOW code, and small modifications were made. Geometry and solid models were created and built using SolidWorks 3D solid modeling software. A prototype ramjet was manufactured with wind tunnel mounting struts capable of measuring axial force on the model. Shadowgraph photography was used in the Mach 4 supersonic wind tunnel at the Naval Postgraduate School's Turbopropulsion Laboratory to verify predicted shock placement, and surface flow visualization was obtained of the airflow from fuel injection ports on the inlet cone of the model. All indications are that the cold-flow tests were successful. / Ensign, United States Naval Reserve

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