Browsing by Author "Kock, M. P."
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- ItemDesign of a cross-over diffuser for a mixed-flow compressor impellor(Stellenbosch : Stellenbosch University, 2017-03) Kock, M. P.; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: This research project focused on the design of a cross-over diffuser for a mixed flow compressor employed in a 600 N thrust micro gas turbine (MGT). Due to the exit of a mixed flow impeller having a meridional discharge angle 2a < 90°, the use of a conventional radial diffuser is inappropriate. The cross over diffuser is a single row diffuser that replaces the conventional two row radial to de-swirler diffuser. The cross-over diffuser is suitable for a mixed flow impeller due to its ability to capture the flow from the impeller without inducing flow separation on the meridional passage walls. The initial cross-over diffuser used in this research was designed using a mean line code. A multi-point optimisation of the mean line design was performed using NUMECA Design3DTM, by means of an Artificial Neural Network incorporated into a Genetic Algorithm. The optimised design showed an increase of 8.75% for the compressor stage total-to-total isentropic efficiency, and a 7.7% increase in total-to-total pressure ratio. The optimised diffuser yielded a large increase in static pressure recovery coefficient of 28.33%. The optimised diffuser static-to-static pressure ratio was increased by 21.5%. The overall operating range remained constant, but the choke mass flow rate increased. The stall mass flow rate also increased, thus shifting the operating range up to a higher mass flow rate. An investigation was also done to evaluate the feasibility of vaneless diffusers by using the same passage of the optimised diffuser in a vaneless format. De-swirlers were also added to the vaneless diffuser. The optimised vaned diffuser outperforms the vaneless diffuser but lacks in operating range.