Thesis (DTech (Mechanical engineering))--Cape Technikon, 1997 / This study forms the basis from which the aerodynamic drag of a practical supersonic inlet can be predicted. In air-breathing propulsion systems, as used in high performance flight vehicles, the fuel is carried onboard and the oxygen required for combustion is ingested from the ambient atmosphere. The main function of the inlet is to compress the air from supersonic to subsonic conditions with as little flow distortion as possible. When the velocity of the vehicle approaches or exceeds sonic velocity (M = 1,0) a number of considerations apply to the induction system. The reason for this is that the velocity of the ingested air has to be reduced to appreciably less than sonic velocity, typically to M = 0,3. Failure to do so will cause the propulsion system to be inoperative and cause damage. In the process of compressing the air from supersonic to subsonic conditions a drag penalty is paid. The drag characteristics are a function of the external geometry and internal flow control system of the inlet. The problem which was investigated dealt with drag of a specific type of inlet, namely a two-dimensional external compression inlet. This study is directed at formulating definitive relationships which can be used to design functional inlet systems. To this effect the project was carried out over three phases, a theoretical investigation where a fluid-flow analysis was done of the factors influencing drag. The second phase covered a comprehensive experimental study where intensive wind-tunnel tests were conducted for flight Mach numbers of M = 1,8; M = 2,0; M = 2,2; M = 2,3 and M = 2,4. During the third phase a comparison, between the theoretical values and experimental data was done, for validating the predicted aerodynamic drag figures. The following findings are worth recording: • the increase in total drag below the full flow conditions is more severe than predicted due to the contribution of spillage drag; • the range for subcritical mode of operation is smaller than expected due to boundary layer effects. The study has shown that reasonably good correlation could be achieved between the theoretical analysis and empirical test at low subcritical modes of operation. This suggests that the study has achieved its primary objective.

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M.Tech. (Mechanical Engineering) / This dissertation focuses on understanding the relation between aerodynamic drag and aerodynamic lift in modern passenger cars and explores what effect these forces have on a vehicle. Modern cars are capable of exceptionally high speed and are subjected to large destabilizing lift forces at these speeds. To counteract the effects of positive lift, various aerodynamic devices and body design details are included in the typical car design. These devices often increase the vehicles aerodynamic drag, reducing energy efficiency as speed increases. The problem that this project aims to address is that at typical commuting speeds where lift forces are low these counter lift devices are not required, however because these devices are fixed the losses associated with their increased drag is still incurred. The devices can however not be excluded from the design as they are required on occasions that the vehicle is driven at abnormally high speed and lift forces become large. The losses associated with the increased drag of such devices are incurred over the vehicles full range of speeds even though the devices are only required at higher speed. The objective of this project is to develop an aerodynamic system that allows the vehicle to continuously and autonomously adjust its drag vs. lift properties to an optimal compromise that suits the vehicles instantaneous aerodynamic requirements. The system offers improvements in both handling and breaking performance as well as increased energy efficiency. The feasibility and effectiveness of the developed system is compared against the performance of a standard test vehicle and against the same test vehicle equipped with various traditional fixed aerodynamic devices. The methods used to develop, analyse and compare the various test models include both practical testing of a physical vehicle and computer based simulation using a digitized model of the same vehicle. Practical testing was conducted at Gerotek test facilities in Pretoria, South Africa and includes measuring the flow rate through the engine cooling system to determine the drag contribution of the cooling system to total vehicle drag. Coast-down testing is used to characterise the test vehicles rolling resistance and skid-pan or circuit tests are used to characterise the vehicles handling properties. Acceleration and breaking tests are also performed. Data from these tests are recorded through various on-board data logging units with pitot tube, GPS and accelerometer devices as inputs. A 3D model of the test vehicle is compiled using photogrammetry software to capture the profile and dimensions of the test vehicle into digital form. A 3D CAD model is developed from the vehicle scan and is used for CFD simulations to solve for the vehicles aerodynamic properties and to assist in the design and incorporation of the various adjustable aerodynamic devices required for the project. The data accumulated through computer simulation and practical testing is combined to form a statistical computer model of the standard vehicle. Research is conducted on existing aerodynamic devices common to passenger cars and suitable devices are adapted to three additional computer models: One with an adaptive aerodynamic system and two with fixed aerodynamic configurations of different intensities. The performance and energy efficiency of the four models are analytically simulated and the results are compared directly. The study shows that in terms of sporting performance around a theoretical road circuit, the adaptive model outperforms both the standard vehicle and fixed configuration models by a small degree, +-2.3%. The standard vehicle is found to have a lift coefficient CL=0.43 with a drag coefficient of Cd=0.31. The dynamic model is able to realize combinations of low drag or low lift between the limits of Cd=0.3, CL=0.34 and Cd=0.32, CL=0.03. The variable aerodynamic properties allow for a 5.5% increase in maximum cornering speed and a 20% improvement in acceleration time from standstill to terminal speed. The percentage improved lap time would be greater if the effects of breaking from the higher terminal speed achieved by the dynamic model were ignored for the simulation...

CD-ROM containing source codes of the numerical scheme (appendix A) is attached to back cover. / Includes bibliographical references (leaves 459-472). / System requirements for accompanying CD-ROM: Macintosh or IBM compatible computer. Other requirements: Adobe Acrobat Reader. / xxxvi, 473 leaves ; ill. ; 30 cm. + 1 computer optical disk (4 3/4 in.) / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A numerical scheme, based on discrete-vortex and surface-vorticity boundary-integral methods, has been developed for stimulating time dependent, two-dimensional, viscous flow over arbitary arrays of solid bodies of arbitary cross-section / Thesis (Ph.D.)--Adelaide University, Dept. of Mechanical Engineering, 2001

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016. / This work presents the computational uid dynamics (CFD) analysis of a light road vehicle. Simulations are conducted using the lattice Boltzmann method (LBM) with the wall adapting local eddy (WALE) turbulence model. Simulations include and compare the use of a rolling road, rotating wheels, adaptive re nement as well as showing comparison with a Reynolds-averaged Navier-Stokes (RANS) solver and the Spalart- Allmaras (SA) turbulence model. The lift coe cient of the vehicle for the most part was seen to show a much greater di erence and inconsistencies when compared to drag from the comparisons of solvers, turbulence models, re nement and the e ect of rolling road. Determining the drag of a road vehicle can be easily achieved and veri ed using multiple solvers and methods, however, the lift coe cient and its validation require a greater understanding of the vehicle ow eld as well as the solvers, turbulence models and re nement levels capable of correctly simulating the turbulent regions around a vehicle. Using the presented method, it was found that the optimisation of vehicle aerodynamics can easily be done alongside the design evolution from initial low-drag shapes to the nal detail design, ensuring aerodynamic characteristics are controlled with aesthetic change.