Tip leakage losses were studied in a linear turbine cascade with a tip clearance gap equal to 2.1 percent of blade height. The blades of the cascade have a turning angle of 109.4 degrees, an aspect ratio of 1.0, and an axial chord length of 235.2 mm. The cascade was located at the exit of a low speed wind tunnel; the blade exit Reynolds number based upon blade axial chord was 4.5x10⁵. The flow was measured at a plane 0.96 axial chords downstream from the blade leading edge. Barlier studies performed at the tip gap exit and at a downstream plane 1.4 axial chords from the blade leading edge were utilized with the present study to understand loss development better. The effect of tip leakage and the corresponding loss production mechanisms involved as the flow mixes out were analyzed. As part of the objective of the study, a computerized data acquisition system was developed which acquires pressure data and controls movement of a five hole pressure probe. The flow properties at the measurement plane were numerically integrated. To estimate the maximum potential loss of the cascade, the flow was mixed-out through a momentum analysis. The loss at the measurement plane due to tip leakage was found to be equal to the sum of the total pressure loss within the tip gap and the dissipated tip gap secondary kinetic energy. As the flow proceeded downstream, losses were attributed to dissipation of secondary kinetic energy, trailing edge wake mixing, endwall losses, and primary flow mixing. / Master of Science

A cross-flow turbine was tested to determine the magnitude of the fluid forces on the blades. The tangential and radial forces and the torque were measured on a test blade. Because the runner was made of plexiglas, the flow and the effects of the incidence angle at various speeds were observed. The pattern of blade loading over a revolution was measured over a range of heads from 1.0 to 2.6 m. The maximum forces were found to occur just before the blade leaves the nozzle exit. The experimental forces agree reasonably well with the results of a control volume analysis. Two figures are provided, by which the designer may determine the tangential and radial forces for any geometrically similar machine. / Master of Science

<p> Continuous development of Gas Turbines to realise higher work output has necessitated the design of turbine blades having large turning angles.</p> <p> Improvements to existing calculation methods have been carried out to better describe the potential flow near the leading and trailing edges of a blade originally designed by R. K. Malhotra at McMaster University. An incompressible turbulent boundary layer program has been extended to calculate compressible flows, taking into account the adverse and favourable pressure gradients, and it has been used to describe the flow in the region near to the blade surface. </p> <p> A test facility of the intermittent blow-down type was constructed and instrumented to test two-dimensional blade cascades. Some of the blades were instrumented to measure the surface pressure distribution. The performance of the blades has been analysed both theoretically and experimentally over a range of angles of attack and pressure ratios. The effect of stagger angle was also investigated to show its effect on performance. The experimental results were compared to those obtained theoretically, and the agreement substantiates the main thrust of the thesis, which was to develop a rational design technique.</p> / Thesis / Doctor of Philosophy (PhD)

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Council for Scientific and Industrial Research has developed a vibration excitation system. The system is designed to excite the rotor blades of an axial compressor in the specified vibration mode and at the specified frequency. The vibration excitation system was tested on Stellenbosch University’s Rofanco compressor test bench. A two-way staggered fluid-structure interaction (FSI) model was created that was capable of simulating the vibration of the rotor blades excited by the system. The results of the FSI model were verified using available experimental data. It was concluded that the FSI model is able to recreate the vibration excited by the system to within the desired level of accuracy. In addition, the results of the FSI model showed that the vibration excitation system should be able to excite the blades in the selected vibration mode and at the selected frequency provided that the excitation frequency is close the natural frequency of the first bending mode. The results also suggested that a transient computational fluid dynamics model should be sufficient for the prediction of the aerodynamic forces acting on the rotor blades. Furthermore, a one-way staggered FSI model should be adequate for calculating the motions of the blades. / AFRIKAANSE OPSOMMING: Die Wetenskaplike en Nywerheidnavorsingsraad het ’n vibrasie-opwekkingstelsel ontwerp om die rotorlemme van ’n aksiaalvloei kompressor in die gespesifiseerde vibrasiemodus en teen die gespesifiseerde frekwensie op te wek. Die vibrasieopwekkingstelsel is met behulp van die Universiteit Stellenbosch se Rofanco kompressortoetsbank getoets. Daarna is ’n tweerigting vloeistof-struktuur-interaksie model geskep om die vibrasie van die rotorlemme, wat deur die stelsel opgewek is, te simuleer. Beskikbare eksperimentele data is gebruik om die resultate van die vloeistof-struktuur-interaksie model te bevestig. Die gevolgtrekking is gemaak dat die model wél die vibrasie van die lemme met die nodige akkuraatheid kan simuleer. Die resultate van die vloeistof-struktuur-interaksie model toon ook dat die stelsel die lemme in die gekose vibrasiemodus en teen die gekose frekwensie behoort te kan opwek, solank die opwekkingsfrekwensie na aan die natuurlike frekwensie van die eerste buigmodus is. Voorts dui die resultate daarop dat ’n berekeningsvloeimeganika model die aërodinamiese laste van die lemme sal kan voorspel. ’n Eenrigting vloeistof-struktuur-interaksie model behoort voldoende te wees om die beweging van die rotorlemme te bereken.