Browsing by Author "Bindeman, Marco"

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    Analysing the performance of a compressor impeller for a micro gas turbine
    (Stellenbosch : Stellenbosch University, 2019-04) Bindeman, Marco; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
    ENGLISH ABSTRACT: This project sets out to numerically evaluate the performance of micro gas turbine (MGT) compressor impellers and to improve the 1-Dimensional (1-D) mean-line code developed for the in-house analysis of these impellers. The objective for the improvement of the code is to accurately predict the performance of both radial flow and mixed-flow impellers. The possible applications for MGTs are numerous. They find specific application for the propulsion of unmanned aerial vehicles (UAVs). Mixed-flow compressors offer the opportunity to reduce the frontal area of a MGT engine while maintaining a high pressure ratio and ensuring a high thrust-to-weight ratio. The use of mixed-flow impellers in MGTs are thus attractive. Although detailed aerodynamic design is normally based on two- and three-dimensional viscous flow analysis, 1-D analysis with empirical work input and loss models is the basis for most aerodynamic performance analyses. Using 1-D mean-line flow analyses also allows the researcher to analyse multiple geometries in a short time span, while only analysing the best performing geometries with 3-D Computational Fluid Dynamics (CFD). Two areas of the mean-line code were identified for improvement. A new slip factor formulation taking both radial and axial flow components into account was implemented. Secondly, an alternative location for the inter-blade throat area was proposed, considering the area between a main blade and splitter blade, as opposed to the area close to the inducer section which is effectively between the main blades. The code was adapted to calculate the throat parameters for the alternative location and two iterations. of the code were subsequently created. The first employing the new slip factor and the second employing both the new slip factor and an alternative throat location. Three diferent impellers, of which one impeller is a mixed-flow impeller, were analysed using the adapted mean-line code and the results were validated with 3- dimensional CFD. The newly adapted 1-D mean-line code was found to predict the performance of the mixed-flow impeller reasonably well. The mean-line code over predicted both the pressure ratio and isentropic efficiency (total-to-total) by 1.6% and 2.8% respectively, while also predicting a larger operating range. The pressure ratio of the centrifugal impellers was under predicted on average by 15%, while the the isentropic efficiency was predicted within 3%. It was however found that a blade outlet angle of 90 adversely affected the performance prediction of the code.