M.Sc. (Mechanical Engineering) / Please refer to full text to view abstract

In two-dimensional flow, the point of flow separation from the surface coincides with the point at which the skin friction vanishes. However, in three-dimensional flow, the situation is much more complex and the flow separation is rarely associated with the vanishing of the wall shear stress except in a few special cases. Though the effects of cross-plane separation are substantial and have been recognized for some time, the phenomenon of flow separation over three-dimensional bodies is still far from being completely understood. The flow is so complex that no completely satisfactory analytical tools are available at the moment. In an attempt to logically identify the various effects and parametric dependence while simultaneously minimizing configuration dependent issue, the flow over a 6 to 1 prolate spheroid, which is a generic three-dimensional body, is investigated. For the identification of the general flow pattern and better understanding of the flow field, surface-oil-flow visualization tests and force and moment tests were performed. The angle of attack effect and Reynolds number effect on the separation location are studied with natural transition. Forces and moments tests, surface pressure distribution measurements as well as the surface presure fluctuations, and mini-tuft flow visualization tests were made to document the flow characteristics on the surface of the body with an artificial boundary layer trip. It was found that there exists a critical Reynolds number at which the flow characteristics of the afterbody changes. This critical Reynolds number was also confirmed by the force and moment tests. Above this Reynolds number, as the Reynolds number increases, the separation lines do not change their circumferential location but stretch to the upstream of the body. For the low supercritical Reynolds number range, the angle of attack effect on the location of the primary separation is not as prominent as in the higher Reynolds number range where the cross-flow component effect becomes dominant. Surface pressure fluctuation data and surface pressure spectra were measured and documented for the first time for this type of three-dimensional flow. For the extension of the study to unsteady transient motion effects, a new Dynamic-Plunge-Pitch-Roll (DyPPiR) model mount was designed and developed to generate required transient motions. The measurements carried out during this study are to be used as reference data to identify the unsteady transient effect of the flow field undergoing unsteady transient maneuvers. / Ph. D.

Surgical Site Infections (SSI) are a significant and potentially preventable source of illness and death for surgical patients. An unknown, but potentially significant fraction of SSI may be caused by airborne infectious particles. Improved or optimized room air distribution may reduce these infections by minimizing the transport of infectious particles into the surgical site. A sophisticated CFD analysis, previously conducted by researchers at the National Institutes of Health (NIH), found that a buoyant thermal plume produced by heat from the surgical site itself could play a significant role in protecting the site from infectious particles. This study experimentally determines the airflow patterns around a simulated patient in a mock operating room using particle image velocimetry (PIV) to find the influence of the buoyant thermal plume on the flow. In addition, independent CFD analysis was performed using a standard commercial CFD program both to help guide and interpret the experimental results and to test the performance of a more readily available tool in predicting the experimental findings. The results of the experimental results and CFD analysis were quantitatively compared to find their agreement.

ENGLISH ABSTRACT: A design routine was derived for designing a series of rotor-only axial flow fans. The routine was applied by designing two different series of axial flow fans. The first design was for a general application rotor-only axial flow fan. This fan series was designed, built and tested in co-operation with Howden Air Industries for both research and commercial purposes. The second design was for a low-noise fan series, which was designed, built and tested by the University of Stellenbosch for research purposes only. The design theory used the principle of blade cropping, meaning that one blade was designed to fit all the different fan sizes. The fan series was designed for diameters ranging from 3 15 mm to 1000 mm. The fan rotors were designed to conform to a velocity profile of minimum exit kinetic flux. The general application fan design was concentrated around the popular fan diameter sizes of 500 rnm, 560 mm and 630 mm and a rotor speed of 1440 rpm, using a commercially available fan series as reference. The low-noise fan design concentrated on one fan size only, namely 630 mm, while also making use of the principle of forward blade sweep. The remaining fan design principles stayed the same as for the general application fan design. The F-series airfoils were used as blade sections for both fan designs. Both fan series were tested for fan noise and performance in accordance with the BS 848 Standards part 1 (1980) and 2 (1985). A selection of fan diameter sizes was tested for the general application fan to verify its perfo!"mance over a range of fan sizes. This indicated a fan series with a wide range of efficient operation, including excellent noise characteristics. A 630 mm diameter fan was used to test the low-noise fan series. It showed both high efficiency and low noise characteristics. The reduction in fan noise achieved with the low-noise fan does not justi1)' the amount of work and costs involved in the designing process, compared to the general application fan. / AFRIKAANSE OPSOMMING: 'n Ontwerpsroetine vir die ontwerp van 'n reeks enkelrotor aksiaalwaaiers is ontwikkel. Die roetine is toegepas deur twee verskillende reekse aksiaalwaaiers te ontwerp. Die eerste ontwerp was vir 'n algemene toepassings enkelrotor aksiaalwaaier. Die waaierreeks is ontwerp, gebou en getoets in samewerking met Howden Air Industries vir beide navorsings - en kommersieIe doeleindes. Die tweede ontwerp was vir 'n lae geraas waaierreeks. Die reeks is ontwerp, gebou en getoets deur die Universiteit van Stellenbosch vir navorsingsdoeleindes. Die onwerpsteorie het gebruik gemaak van die beginsel van lemverkorting, waardeur een lem ontwerp is om op al die groottes waaierdeursnee te pas. Die waaierreekse is ontwerp vir waaierdeursnee tussen 315 mm en 1000 mm. Die rotors is ontwerp om 'n uitlaatsneIheidsprofiel te gee wat 'n minimum verlies in kinetiese energie toelaat. Die algemene toepassings waaierontwerp het gekonsentreer rondom die gewilde waaierdeursnee van 500 mm, 560 en 630 mm. Dit is ontwerp vir 'n rotorspoed van 1440 met 'n kommersieel beskikbare waaierreeks wat as verwysing gebruik is. Die lae geraas waaierreeks het op slegs een waaiergrootte gekonsentreer, naamlik 630 mm. Die lae geraas waaierreeks is ook ontwerp met vorentoe gekurfde lemme. Die res van die ontwerpsbeginsels was dieseIfde as vir die algemene toepassings waaierreeks. Die F-reeks vleuelprofiele is gebruik vir die lemseksies van beide waaierreekse. Beide waaiereekse is getoets vir waaiergeraas en -effektiwiteit deur gebruik te maak van die BS 848 Standaarde deel 1 (] 980) en 2 (] 985). 'n Verskeidenheid van waaierdeursnee van die algemene toepassings waaierreeks is getoets om die waaier se vertoning oor 'n gebied van waaiergroottes te bepaal. Die resuItaat was 'n waaierreeks met 'n wye gebied van effektiewe werking, asook uitstekende geraaseienskappe. 'n 630 mm Deursnee waaier is gebruik om die lae geraas waaier te toets. Die toetse het 'n waaier getoon wat beide hoe effektiwiteit en lae geraaseienskappe het. Die afname in waaiergeraas wat verkry is met die lae geraas waaier, in vergelyking met die algemene toepassings waaier, regverdig egter rue die werk en kostes verbonde aan die ontwerp van die waaierreeks nie.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The aerodynamic performance of a mission-adaptive air inlet for a stealthy unmanned aircraft was examined using CFX 5.5, a commercial Computational Fluid Dynamics package. In order to ensure that the numerical results were reliable, the package was validated against a number of flow situations for which previously-known results exist. This was done for both external and internal flow, and in all cases the conclusion could be made that the code produces realistic results. The simulation of the inlet was done in two steps. A first-order design was simulated using robust simulation parameters: the focus was on obtaining a "picture" of the flow into the inlet, not on the quantitative values of flow variables. On account of the results of these simulations, the design was suitably modified. This second-order design was then simulated using more accurate simulation parameters, and the results analysed in detail. Comparative simulations between the two design iterations showed that their pressure recoveries are similar, but that the distortion of the velocity profile at the engine compressor face is lower for the second-order design than for the first-order design over a significant portion of the operational range. When compared with an idealized theoretical analysis, the numerical results showed that the performance of the inlet was severely degraded at most operating conditions. This is mainly due to the effects of flow separation ahead of the inlet capture plane. To alleviate this problem, recommendations for the modification of the design are proposed. This thesis demonstrates that CFD is a valuable tool for both qualitative and quantitative evaluation of performance during the design process of an air inlet. / AFRIKAANSE OPSOMMING: Die lugdinamiese werkverrigting van 'n missie-aanpasbare luginlaat vir 'n radarontduikende onbemande vliegtuig is ondersoek, deur gebruik te maak van CFX 5.5, 'n kommersiële numeriese vloeidinamika-sagteware pakket. Om te verseker dat die numeriese resultate betroubaar was, is die pakket gevalideer teen 'n aantal gevalle waarvoor vooraf-bekende resultate bestaan. Dit is gedoen vir beide interne en eksterne vloei, en die gevolgtrekking kon gemaak word dat die kode wel realistiese resultate lewer. Die simulasie van die inlaat is in twee stappe gedoen. 'n Eerste-orde ontwerp is gesimuleer deur gebruik te maak van robuuste simulasieparameters: die fokus hiervan was om 'n visuele indruk van die vloeipatrone in die inlaat te kry, nie op kwantitatiewe waardes van die vloeiveranderlikes nie. Na aanleiding van hierdie resultate van hierdie simulasies is die ontwerp dienooreenkomstig aangepas. Hierdie tweede orde ontwerp is dan gesimuleer deur gebruik te maak van meer akkurate simulasieparameters, en die resultate is in detail geanaliseer. Vergelykende simulasies tussen die twee ontwerps-iterasies het gewys dat hulle drukherwinnings soortgelyk is, maar dat die distorsie in die snelheidsprofiel by die enjin kompressor-vlak laer is vir die tweede-orde ontwerp as vir die eerste-orde ontwerp, oor 'n beduidende gedeelte van die operasionele bestek. Wanneer dit met 'n ideale teoretiese analise vergelyk word, het die numeriese resultate getoon dat die werkverrigting van die inlaat ernstig gedegradeer is by meeste operasionele toestande. Dit kan meestal toegeskryf word aan die effekte van vloei-wegbreking voor die intreevlak van die inlaat. Om hierdie probleem te verlig, word aanbevelings vir die aanpassing van die ontwerp voorgestel. Hierdie tesis demonstreer dat numeriese vloeidinamika waardevolle gereedskap is vir beide kwalitatiewe en kwantitatiewe evaluering van werkverrigting tydens die ontwerpsproses van 'n luginlaat.

published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

In various industries, specialized filters with activated carbon are used for adsorbing mercury from air-flows. MRT has eight such Activated CarbonFilters (ACFs) in one of their devices. The main purpose of research is tostudy the flow in the ACF filter and suggest a mathematical model for the complete system through which an improved design can be found.Simulation of a single ACF illustrates how the current system’s air flow does not cover the whole filter leaving part of the carbon bed unused forthe adsorption. This is validated by experimental data. A theoretical studybased on a mathematical model is made and the improved air flow pattern of a re-designed ACF is presented. An additional improvement is that byswitching inlet and outlet the usable time of the filters is prolonged.

Master of Science / Department of Mechanical and Nuclear Engineering / B. Terry Beck / The purpose of the research was to quantify the influence of several duct disturbances on volumetric flow rate measurements and use these in developing guidelines for field technicians. This will assist the field technicians in making more accurate volumetric air flow measurements in rectangular ducts during a test and balance operation. Multiple duct sizes, fittings, probes, traverse algorithms, and locations upstream and downstream of the disturbances are used to compare a variety of situations. The two traverse algorithms used are the log-Tchebycheff and equal area methods. Two upstream and five downstream locations are tested for each duct configuration. Two air velocity probes are used for local velocity measurements on each traverse: a pitot-static probe and a hot wire anemometer. A nozzle bank and Air Flow Measurement Station are used as the flow measurement standards for comparison with each traverse. This paper discusses the setup and initial results of ASHRAE 1245-RP. Data collected subsequent to this thesis will complete the balance of results and will be collected and analyzed by other researchers. Results will be summarized and presented in a way which allows technicians to use it in the field for more accurate balancing results.

Neste trabalho pretende-se desenvolver o dispositivo para a fixação de cabeçotes e acionamento de válvulas em um equipamento para medição de swirl, que é um dos movimentos do ar dentro da câmara de combustão nos motores de ignição por compressão. Este desenvolvimento tem como objetivos facilitar a montagem do cabeçote no equipamento e desenvolver o avanço automático das válvulas, visando a redução do tempo total do ensaio. No desenvolvimento, foi feito um comparativo das características e componentes montados nos cabeçotes e nos diferentes modelos que serão testados no equipamento, para que não fossem necessários retrabalhos no cabeçote ou desmontagens de componentes para a realização dos ensaios, abrangendo a maior gama possível de produtos. Foram definidos os métodos de posicionamento do cabeçote no dispositivo e o sistema de fixação. Para garantir a precisão no acionamento das válvulas, foi definido um fuso de esferas recirculantes, acionadas por um motor de passo. O projeto foi concluído e o dispositivo foi fabricado e instalado no equipamento de medição. Testes realizados mostraram resultados de medição de swirl conforme esperado, além da diminuição no tempo total do teste. A partir de observações feitas após a fabricação e os testes no dispositivo, algumas melhorias estão sendo propostas, como, por exemplo, acionamentos por balancins independentes para cada válvula. / In this work, the aim is to develop the device for the fixture of the cylinder head and the valve actuation in a swirl meter test bench. Swirl is a movement inside the combustion chamber in a compression ignition engine. The development aims to facilitate the assembling of the cylinder head in the equipment and develop the valve lift device, focusing in decreasing the total time for the test. Also, the valve actuator shall be able to perform the continuous valve lift in the swirl measurement. During the development of this work, a comparative of the main features and the components assembled in the different cylinder head types to be tested in the equipment was done, to avoid rework or disassembling of components for the test, including the most variety of types. It was defined the positioning method for cylinder head in the device and the fixation system. To ensure the precision in the valve actuation, it was defined a ball screw, driven by a step motor. The project was finalized, manufactured and installed in the measurement equipment. Performed tests have showed results of swirl measurement according to expected, and the total time of test was decreased. After this first project, some improvements are proposed in the device, for example, individual actuation per valve.