Browsing by Author "Tilahun, Nigussie"

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    Aerothermodynamics Analysis of Axial Flow Aircraft Gas Turbine Engine Compressor
    (Addis Ababa University, 2009-10-05) Tilahun, Nigussie; Tesfaye, Dama (PhD)
    The axial flow type compressor is one of the most common compressor types in use today. It finds its major application in large aircraft gas turbine engine like those that power today’s jet aircraft. Early axial flow aircraft engine compressors had pressure ratio of around 5:1 and require about 10 stages. Over the years the overall pressure ratios available exceed 30: 1 due to continued aerodynamic development that resulted in a steady increase in a stage pressure ratio with reduced number of stages. There has been in consequence a reduction in engine weight for a specific level of performance, which is particularly important for aircraft engines. These potential gains have now been fully realized as the result of intensive research into the Aero-thermodynamics Analysis of Axial Flow Aircraft Gas Turbine Engine Compressor. Therefore, careful design of compressor blading based on aero-thermodynamic theory, experiment and computational fluid dynamic (CFD) analysis is necessary not only to prevent useful losses but also to insure a minimum of stalling troubles. The complete analysis of this thesis is done to provide some part of design of an axial compressor suitable for a simple low-cost and low weight turbojet Aircraft Gas Turbine Engine Compressor by using different research work on the aero-thermodynamic analysis of the compressor. Details of CFD analysis on the models of the compressor, using a commercial software “FLUENT”, will be presented. The CFD simulation predictions were validated quantitatively against the experimental data and the theoretical (calculated values) were then used to obtain further insights into the characteristics of the flow behaviors. To calculate the work and power required by the compressor to sustain the flight, the blades of the compressor will be modeled, and the required equations will be developed. Finally a small scale computer program will be developed to calculate the power (work) required by the compressor and to determine other performance measuring parameters.
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    CFD Based Design Optimization, Fabrication and Testing of A Micro Hydro Pelton Turbine
    (Addis Ababa University, 2018-12) Tilahun, Nigussie; Edessa, Dribssa (PhD)
    In areas where the supply of grid power is very difficult, utilisation of Micro hydro-power as renewable energy source is of great concern now a-days to eliminat extreme poverty around the world. These schemes can provide environmentally sustainable electricity and mechanical power to rural communities. For this purpose, selected types of micro hydro turbines need to be designed and developed depending up on the site locations. Thus, considering the potential of hydropower generation in Ethiopia, this research addresses the design, optimization, local manufacturing, and experimental test of a model of micro hydro Pelton turbine for one of the selected potential site (Indris River) in South West Shewa of Ethiopia to meet the requirements of the energy demands of the nearby village as a case study. Initially, the geometries to be compared (baseline design of the turbine) were done with the design guide lines and tested by developing numerical model using commercial CFD. Considerations are taken in designing the turbine with an effective post life recycling scheme in mind so that there will be minimum wastage of resources once the turbine is made redundant. CFD simulations using ANSYS-CFX were conducted, to optimize further the bucket shape in order to get a cost effective runner design. Additionally, consequences of variation in each design parameter were evaluated from the baseline design. The result of the study proposes some modifications in the baseline design. Through the analysis, a weight reduction of around 7.6% is achieved due to the modified runner design. Moreover, CFD was predicting a 3.9 % improvement of hydraulic efficiency. The optimization of number of buckets, length, depth and shape of the lip curve are the main design parameters for the achieved improvement in efficiency. It is then checked for structural safety with a more accurate method using ANSYS. At a later stage, the model was experimentally tested at the AAIT Lab to have a tangible confirmation of efficiency at variable operational conditions. The experimental results confirmed a 2.8% improvement in efficiency. This prediction was validated for the modified runner design used in the simulation using the same head and flow rate conditions as for the baseline design. Overall, the comparative results with CFD were satisfactory and in line with the theory, and verifying the turbine model design effectiveness which will be useful for implementation of rural electrification projects.