<p> The thesis is concerned with the design and construction of an instrumentation system for a machine set in a power laboratory. As the system was designed primarily to replace conventional analog metering its operation is very easy to master given minimal instruction. The system is capable of measuring rotor speed, rotor angle and reactive torque. From these values mechanical power and slip are calculated. While acting as a measuring instrument the system can also simultaneously provide speed setting of a dc machine by means of a controlled rectifier. As this system is constructed around a microcomputer it is possible to expand some of the functions as well as interconnect to other digital devices for enhanced performance.</p> / Thesis / Master of Engineering (MEngr)

The importance of sports engineering has increased in the past decade as the demand for athletes and their equipment has increased. Similarly, the aerodynamics of blunt bodies such as prolate spheroids is of particular interest to aerodynamicists seeking to reduce drag. A system was developed to measure aerodynamic forces on rugby balls. The rugby balls, which varied in size and surface textures, were tested at multiple angles of attack, rotational rates, and wind tunnel velocities. A force balance utilizing load cells in conjunction with a subsonic wind tunnel was used to obtain lift and drag forces. A detailed description of the complete test apparatus is given including methods of mounting, rotation, calibration and tare measurements. Several methods of data acquisition were investigated and the final method is outlined. The results for two balls are given along with the variation in data from repeated testing. Both the force data trends and a few interesting phenomena are discussed.

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The rolling of an aircraft about its fuselage produces centrifugal forces which affect the stiffness of the wings. A number of previous studies explain the effect of centrifugal stiffening in rotating beams and consequently on the frequencies of the beam. Multiple cases of the rotating beam are explored in this thesis to investigate effects of mass distribution and boundary conditions on the frequencies of centrifugally stiffened beams. It is found that for a uniform beam with all degrees of freedom free on both ends, the rigid modes of the beam are affected and are no longer zero when it is stiffened from centrifugal forces. This thesis aims to set up a model to investigate the stiffening effects using the mAEWing2 aircraft. A preliminary analysis is done for the mAEWing2 aircraft and the roll rate, control surface deflection and angle of attack are identified as the parameters to be studied. For a given angle of attack and control surface deflection, the centrifugal forces in the aircraft in steady roll are determined using trim analysis. These are used to pre-stress the model for modal analysis. It is found that in mAEWing2 aircraft in steady roll maneuvers, the centrifugal stiffening effect on the natural frequencies is not significant. It emphasizes the need to conduct a sensitivity analysis to include centrifugal stiffening in the dynamic analysis while designing an aircraft. This, along with some de-stiffening due to gravity loads might be important for the future N+3 aircraft with their high aspect ratio large wingspans. / MS

This work studies the effects of radial flow on the aerodynamic phenomena occurring on a retreating blade with a focus on dynamic stall and reverse flow as applied to both a helicopter rotor in forward flight and a wind turbine operating at a yaw angle. While great progress has been made in understanding the phenomenon of two-dimensional dynamic stall, the effect of rotation on the dynamic stall event is not well understood. Experiments were conducted on a rigid two bladed teetering rotor at high advance ratios in a low speed wind tunnel. Particle image velocimetry (PIV) measurements were used to quantify the flow field at several azimuthal angles on the rotating blade during the dynamic stall event. The effect of centrifugal forces induced ``pure'' radial velocity on the dynamic stall event at 270 degrees azimuth was studied in detail. Further investigation of the radial flow field suggested that the mean radial velocity attenuated on moving outboard due to an apparent shear layer instability and it was demonstrated to be of first order importance in the flow field. These radial flow results prompted an exploration of the flow over a rotating disk to establish similarities of the radial flow over rotating blade in separated flow to that over a rotating disk in separated flow. While a greater part of this work focused on aspects of dynamic stall on the retreating blade, the final parts focus on the exotic flow regime of reverse flow (characterized by flow from the trailing edge to the leading edge of the blade). Aerodynamic loads measurement and surface flow visualization via tufts are used to first quantify the behavior of a static yawed blade in reverse flow. PIV measurements are then used on a static yawed blade and a rotating blade in reverse flow conditions to ascertain the effects of rotation on reverse flow.

This work investigated a numerical approach to the search of a maximum heat transfer rate density (the overall heat transfer dissipated per unit of volume) from a two-dimensional laminar multiscale array of cylinders in cross-flow under an applied fixed pressure drop and subject to the constraint of fixed volume. It was furthermore assumed that the flow field was steady state and incompressible. The configuration had two degrees of freedom in the stationary state, that is, the spacing between the cylinders and the diameter of the smaller cylinders. The angular velocity of the cylinders was in the range 0 ≤ ϖ, ≤ 0.1. Two cylinders of different diameters were used, in the first case, the cylinders were aligned along a plane which lay on their centrelines. In the second case, the cylinder leading edge was aligned along the plane that received the incoming fluid at the same time. The diameter of the smaller cylinder was fixed at the optimal diameter obtained when the cylinders were stationary. Tests were conducted for co-rotating and counterrotating cylinders. The results were also compared with results obtained in the open literature and the trend was found to be the same. Results showed that the heat transfer from a rotating array of cylinders was enhanced in certain cases and this was observed for both directions of rotation from an array which was aligned on the centreline. For rotating cylinders with the same leading edge, there is heat transfer suppression and hence the effect of rotation on the maximum heat transfer rate density is insignificant. This research is important in further understanding of heat transfer from rotating cylinders, which can be applied to applications ranging from contact cylinder dryers in the chemical processes industry and rotating cylinder electrodes to devices used for roller hearth furnaces. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

The tip generation/substrate collection mode (TG/SC) of scanning electrochemical microscopy (SECM) was used to study the ORR reactivity on Pt catalysts in sulfuric acid solution. The SECM reactivity image and the photographic image of different single crystalline regions of the etched Pt electrode correlated well. The electron backscatter diffraction (EBSD) image of Pt confirmed the surface single crystalline orientation. The image resolution is improved by employing smaller tip-substrate distance. The kinetics of the ORR on Pt surface was also studied at -15 - 30 C by means of the rotating disk voltammetry techniques. The calculated Tafel slopes for 0.1 m and 0.9 m HClO4 changed with decreasing temperature, indicating lower kinetics at low temperature. Peroxide is produced at potentials below 0 V vs SCE.