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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

Design of 120cc Single Cylinder Experimental Engine for Analysis of Intake Swirl and Multiple Ignition Sites.

Seemann, Patrick 01 January 2009 (has links)
The intent of this thesis is to design, build, and test a cylinder head with variable swirl and ignition sites. The design aspect used Solid Works Floworks to model airflow within the head and cylinder. Swirl rate and volumetric flow rate were calculated from the results. Many design iterations took place before a suitable design was accomplished. Once the suitable design was reached, it was built using the rapid prototyping method known as 3-D printing (Fused Deposition Modeling). Valve guides and seats were installed in the head. Then valves, springs, and retainers were installed to allow for testing. The inlet was created using stereo-lithography due to its smooth surface finish and thin walls. A pin wheel swirl measuring device was built to measure tangential rotation rate of gasses in the cylinder. The experimental head was tested on the University of Miami flow bench in the Internal Combustion Engines Laboratory. The results of the experimental work and theoretical modeling were compared. The results matched closely. The difference between experimental and theoretical values for high swirl flow rates were less than 3% error and the swirl ratio was less than 10%. For the low swirl scenario, error was less than 30%. The measured flow rate for the high swirl scenario was 28.87 CFM and the swirl ratio was measured as 2.87. SolidWorks Floworks created accurate results for the high swirl scenario and further experimentation should be conducted for different geometries.
2

CFD Simulation of Multi-Dimensional Effects in Inertance Tube Pulse Tube Cryocoolers

Cha, Jeesung Jeff 12 April 2004 (has links)
Inertance Tube Pulse Tube Cryocoolers (ITPTC) are a class of rugged and high-endurance refrigeration systems that operate without a moving part at their low temperature end, and are capable of reaching 4 K or lower. ITPTCs are suitable for application in space vehicles, and attempts are underway worldwide to improve their performance and miniaturize their size. The thermo-fluidic processes in ITPTC are complicated, however, and the details of the mechanisms underlying their performance are not well understood. Elucidation of these underlying processes is the objective of this investigation. In this study, the commercial computational fluid dynamic (CFD) package Fluent䵠was utilized for modeling the entire large ITPTC system that includes a compressor, an after cooler, a regenerator that is represented as a porous medium, a pulse tube, cold and warm heat exchangers, an inertance tube, and a reservoir. The simulations represent a fully-coupled system operating in steady periodic mode, without any arbitrary assumptions. The objective was to examine the extent of multi-dimensional flow effects in an inertance tube pulse tube cryocoolers, and their impact on the performance of these cryocoolers. Computer simulations were performed for two complete ITPTC systems that were geometrically similar except for the length-to-diameter ratios of their regenerators and pulse tubes. For each ITPTC system three separate simulations were performed, one with an adiabatic cold-end heat exchanger (CHX), one with a known cooling heat load, and one with a pre-specified CHX temperature. Each simulation would start with an assumed uniform system temperature, and continue until steady periodic conditions were achieved. The results indicate that CFD simulations are capable of elucidating the complex periodic processes in PTCs very well. The simulation results also show that a one-dimensional modeling of PTCs is appropriate only when all the components of the PTC have very large aspect ratios (i.e., L/D >>1). Significant multi-dimensional flow effects occur at the vicinity of component-to-component junctions, and secondary-flow recirculation patterns develop, when one or more components of the PTC system have small aspect ratios. The simulation results, although limited in scope, also suggest that ITPTCs will have a better overall performance if they are made of components with large aspect ratios.
3

A numerical method for fully nonlinear aeroelastic analysis

Gargoloff, Joaquin Ivan 15 May 2009 (has links)
This work presents a numerical method for the analysis of fully nonlinear aeroelastic problems. The aeroelastic model consisted of a Navier-Stokes flow solver, a nonlinear structural model, and a solution methodology that assured synchronous interaction between the nonlinear structure and the fluid flow. The flow around the deforming wing was modeled as unsteady, compressible and viscous using the Reynolds-averaged Navier-Stokes (RANS) equations. To reduce the computational time, a three-level multigrid algorithm was implemented and the flow solver was parallelized. The message-passing interface (MPI) standard libraries were used for the parallel interprocessor communication. The computational domain was divided into topologically identical layers that spanned from the root to past the tip of the wing. A novel mesh deformation algorithm was developed to deform the mesh as the structure of the wing was being displaced. The mesh deformation algorithm was able to handle wing tip deformations of up to 60 % of the wing semi-span. Besides being robust, the mesh deforming algorithm was computationally more efficient than regriding, since deforming an existing mesh was computationally less expensive than generating a new mesh for each wing position. Results are presented for the validation and verification of both the flow solver and the aeroelastic solver. The flow solver was validated using: (1) the flow over a flat plate, to validate the turbulent model implementation, and (2) the flow over the NACA 0012 airfoil and over the F-5 wing, to validate the implementation of the convective and viscous fluxes, the time integration algorithm, and the boundary conditions. The aeroelastic solver was validated using: (1) the unsteady F-5 wing undergoing forced pitch motion, and (2) the Nonlinear Aeroelastic Test Apparatus (NATA) wing. In addition, aeroelastic results were generated for the Goland wing. The aeroelastic solver developed herein allows the analysis of aeroelastic phenomena using a fully nonlinear approach. Limit cycle oscillations, which are highly nonlinear phenomena, were captured by the nonlinearities of the flow solver and the structural solver. The impact of the nonlinearities was assessed for the Goland wing, where nonlinear terms changed dramatically the aeroelastic behavior of the wing.
4

An Evaluation of Turbulence Models for the Numerical Study of Forced and Natural Convective Flow in Atria

CABLE, MATTHEW 21 May 2009 (has links)
A demand for methods that can be used in the numerical analysis of three dimensional air flow in large buildings has developed as more buildings are being designed with large atriums using a solar loading that leads to complex flow. The flow in such buildings is almost always turbulent which means that turbulence models that are accurate but which do not require undue computer resources have to be selected. As a result, a numerical study of natural convective heat transfer and turbulent flows in large atria, specifically part of the Atria in the EV building at Concordia University, has been completed. Experimental work on turbulence modeling and atria design has been studied and compared with the numerical results obtained here to gain confidence in the modeling techniques used in the study. The flow has been assumed to be steady, and the Boussinesq approximation has been used. The governing equations have been numerically solved using the CFD solver FLUENT. The three-dimensional air flow in the Concordia-like atria used the following parameters: forced flow vent inlet angle; forced flow vent velocity; date and time (for solar radiation purposes). The case with adiabatic floor and ceiling conditions was examined and compared to the case with isothermal floor and ceiling conditions. Several models were studied to compare the effect of turbulent modeling in the atria, including the following: (1) K-Epsilon; (2) K-Omega; (3) Detached Eddy Simulation (DES) model; (4) Large Eddy Simulation (LES) model. Further study was completed after it was noted the flow was completely based on natural convection when the velocity of the inlet flow was set to zero. In addition, experimental results were available and this situation was modeled using similar parameters to the work explained above. Comparing these results supported the accuracy of the work done on the Concordia Atrium. Experimental work on the Annex 26 Atrium in Yokohama Japan was also compared to numerical results to gain confidence in techniques used in the present study and results were obtained that were in good agreement. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-05-21 16:21:27.82
5

Evaluation of the potential of solar chimneys to drive natural ventilation in non domestic buildings

Swainson, M. J. January 1997 (has links)
The solar chimney allows natural ventilation to be achieved during periods when the wind velocities are low and the difference between internal and external air temperatures is minimal. The correct design of such building components requires that designers have appropriate design tools available to them that are both effective and easy to use. The aim of this project was to evaluate design tools currently available and if appropriate to provide a tool that would allow the effects of variations in key physical parameters to be evaluated. Two design tools are currently available to designers; zonal models and CFD programmes. Both of these were however found to be unsuitable for the evaluation of the performance of a solar chimney. Zonal models assume that the air within a zone is fully mixed which results in the effects of variations in physical parameters on the mass flow rate being incorrectly predicted. CFD programmes require validation of any models developed before confidence in the predictions can be established, it was found however that data for such validation was not available for realistic flow configurations. An experimental rig was designed and tested to ensure that the uncertainty in the data produced was both minimised and accurately quantified. A detailed review of the sensitivity of a CFD programme to model and input variables was undertaken allowing development of an appropriate model. Comparison of the results of the experimental investigation and CFD predictions showed that the CFD programme, utilising the ke turbulence model accurately predicted air flow rates through a solar chimney across a range of key physical parameter variations. Within the limits of the validity determined for the CFD model, a detailed parametric investigation was then undertaken. The result of the parametric investigation was the development of a design tool appropriate for the determination of the effects of variations of the key physical variables on the mass flow rate through a solar chimney.
6

Experimental and CFD Study of Wind-Induced Response for Bridge Cables with Ice accretion

Songyu, Cao January 2015 (has links)
Cable-stayed bridges are massive structures which rely on their structural elements such as deck girder, towers and stay-cables for their stability. The bridge stay-cables can be considered as the most flexible elements of the cable-stayed bridges, and thus their structural stability integrity is verified for several phenomena which might affect them. Wind and wind/rain induced vibrations for bridge stay-cables were comprehensively studied by researchers worldwide; however recent projects have identified a new type of cable vibrations caused by ice accretion formed around the cable circumference. The current research proposed two ice accretion profiles for inclined bridge cables and has experimentally investigated the wind-induced vibrations of the two models for the bridge stay-cables with ice accretion, under different vertical (inclination) and horizontal (yaw) angles, and for different wind speeds. Initially, three models of the bridge cable with 1.0 cm and 2.0 cm ice profile were tested in the wind tunnel of cross-section 61 cm × 90 cm, and a maximum wind speed of 30 m/s. In total 6 cases with 1.0 cm ice thickness and 3 cases with 2.0 cm ice thickness were investigated and the vertical and torsional oscillatory displacements were recorded for wind speeds from 1.5 m/s to 15 m/s at intervals of 1.5 m/s. The wind-induced vibrations were analyzed and were compared with the response reported for cables without ice and with the rain-induced response for stay-cables. Computational Fluid Dynamics (CFD) simulations were performed to observe the drag, lift and pressure coefficients around the surface of the accreted cable models yawed and inclined at α = 0°, β = 0° and α = 60°, β = 15° under the effect of 10 m/s and 15 m/s wind speed applied for both cases. A verification for galloping divergent instability was conducted based on the Den Hartog formulation and the vertical vibrations obtained from the wind tunnel experiment.
7

A Detailed Look into the Aerodynamic Forces Due to the Drag-Reducing Aerospike

Douglas, Philip 09 December 2016 (has links)
This thesis aims to simulate previous wind tunnel experiments on the drag-reducing aerospike in order to help validate the accuracy of CFD analysis. Multiple grids were created with the Pointwise grid generation software. The CFD analysis software used was Ansys Fluent, with both planar and axisymmetric cases being tested for the primary rocket in order to compare the differences. The tests with the primary rocket followed how a spike of set length reacted at various speeds. Two additional experiments were duplicated. These helped confirm that the results obtained via Fluent were accurate. One case was a simple transonic spike model, and the other was a more complex hypersonic model. The results from both cases matched well with wind tunnel tests, validating results for the primary rocket. This thesis paves the way for anyone wanting to continue a more in depth study into the flow properties of any type of projectile.
8

Investigation of the Capability of a Computational Fluid Dynamics Code for Low Reynolds Number Propeller

Harich, Naoufal 06 May 2017 (has links)
The amount of research and publication on low Reynolds number propellers has increased recently, especially because of the high number of UAVs produced during the past years. The use of CFD on propellers has been focused primarily on commercial propellers, propfans, and general aviation propellers. The aim of this work is to use a CFD code designed mainly for large scale (i.e. high Reynolds number) propellers to compute the performance characteristics of a low Reynolds number propeller and then compare those results with another software product that has been used more for low Reynolds number propellers.
9

Investigation of the Turbulent Flow and Heat Transfer around a Heated Cube Cooled by Multiple Impinging jets in a Cross-Flow

Johansson, Robert January 2016 (has links)
The fast development in electronics has resulted in faster and faster computers. Furthermore, the electronic components trend to get smaller and smaller by the year. With more processing power combined with smaller components the heat generation rapidly increases. The scope of this study is to examine a spot cooling technique consisting with different geometry of multiple impinging jets in combination with a cross-flow by the use of CFD. The case is limited to a heated wall mounted cube cooled by a impinging jet as well as an multiple impinging jets in a low velocity cross-flow. This study can be divided into two parts a verification study and a detailed study. The verification study consist of comparison between RSM model and measured values for both the turbulent flow and the surface temperature. The single impinging mesh consists of 934 k elements while the plus 1439 k and cross consists of 2809 k elements. All the meshes are created in ANSYS fluent and this paper contains a detailed guide to create them. The verification study proved that RSM can predict the complicated flow with good agreement with the single impinging jet. The heat transfer coefficient differ substantially between the cases. The PIV compared to the UDF for the inlet velocity profiles had a 21\% increase in heat transfer coefficient in the top layer of the cube. In all the simulations the cross had at least an increase of 18\% on average \(h\). While there was no real verification study for the multiple impinging jets I would still argue that cross is better than the plus sign geometry in terms of heat transfer.
10

Prediction of ignition limits with respect to fuel fraction of inert gases. : Evaluation of cost effective CFD-method using cold flow simulations

Sjölander, Johan January 2015 (has links)
Improving fuel flexibility for gas turbines is one advantageous property on the market. It may lead to increased feasibility by potential customers and thereby give increased competiveness for production and retail companies of gas turbines such as Siemens Industrial Turbomachinery in Finspång. For this reason among others SIT assigned Anton Berg to perform several ignition tests at SIT’s atmospheric combustion rig (ACR) as his master thesis project. In the ACR he tested the limits for how high amounts of inert gases (N2 and CO2) that the rig, prepared with the 3rd generation DLE-burner operative in both the SGT-700 and SGT-800 engine, could ignite on (Berg, 2012). Research made by Abdel-Gay and Bradley already in 1985 summarized methane and propane combustion articles showing that a Karlovitz number (Chemical time scale/Turbulent time scale) of 1.5 could be used as a quenching limit for turbulent combustion (Abdel-Gayed & Bradley, 1985). Furthermore in 2010 Shy et al. showed that the Karlovitz number showed good correlation to ignition transition from a flamelet to distributed regime (Shy, et al., 2010). They also showed that this ignition transition affected the ignition probability significantly. Based on the results of these studies among others a CFD concept predicting ignition probability from cold flow simulations were created and tested in several applications at Cambridge University (Soworka, et al., 2014) (Neophytou, et al., 2012). With Berg’s ignition tests as reference results and a draft for a cost effective ignition prediction model this thesis where started. With the objectives of evaluating the ignition prediction against Berg’s results and at the same time analyze if there would be any better suited igniter spot 15 cold flow simulations on the ACR burner and combustor geometry were conducted. Boundary conditions according to selected tests were chosen with fuels composition ranging from pure methane/propane to fractions of 40/60 mole% CO2 and 50/75 mole% N2. By evaluating the average Karlovitz number in spherical ignition volumes around the igniter position successful ignition could be predicted if the Karlovitz number were below 1.5. The results showed promising tendencies but no straightforward prediction could be concluded from the evaluated approach. A conclusion regarding that the turbulence model probably didn’t predict mixing good enough was made which implied that no improved igniter position could be recommended. However by development of the approach by using a more accurate turbulence model as LES for example may improve the mixing and confirm the good prediction tendencies found. Possibilities for significantly improved ignition limits were also showed for 3-19% increase in equivalence ratio around the vicinity of the igniter.

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