Browsing by Author "Swanepoel, Pieter Coenraad"
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- ItemThe Experimental evaluation of a mixed-flow compressor impeller and cross-over diffuser.(Stellenbosch : Stellenbosch University, 2018-12) Swanepoel, Pieter Coenraad; Van der Spuy, S. J.; Von Backström, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: In the past decade Stellenbosch University has been actively involved in the development of components for Micro-gas turbines (MGTs). MGTs are particularly attractive to the energy and defence sector due to their high thrust-toweight ratio and thus relatively high power output. The use of a mixed-flow compressor impeller is attractive for MGTs due to its mass flow vs pressure ratio characteristics. Previous researchers optimised and manufactured a mixedflow compressor impeller and cross-over diffuser for this specific reason. The goal of this thesis is to experimentally validate the numerical predictions made for the compressor stage with the computational fluid dynamics (CFD) code NUMECA. Experimental tests were conducted with a compressor test bench in the Gas Dynamics Laboratory at Stellenbosch University. The air receiver capacity limited the operational speed of the facility to 50 000 rpm. The performance of the impeller is evaluated numerically and experimentally with both a cross-over and vaneless diffuser. The effect of trailing edge blade tip clearance on the performance of the impeller is also investigated numerically and experimentally. The assembly of the test bench allowed for design modifications to be made to the shaft, bearing housing, split ring spacer and bearing layout. The modifications proved beneficial as experimental tests were conducted successfully at 50 000 rpm. The experimental results agreed well with the numerical results with the vaneless diffuser assembly delivering a total-tototal pressure ratio of 1.57 with an efficiency of 71.0% at a mass flow rate of 0.26 kg=s. The cross-over diffuser assembly delivered a total-to-total pressure ratio of 1.63 with an efficiency of 76.3% at a mass flow rate of 0.3 kg=s. The effect of blade tip clearance on the impeller’s performance was notable with the cross-over diffuser assembly but could not be observed with the vaneless diffuser assembly. A trailing edge blade tip clearance of 0.2 mm was also achieved experimentally and proved to be feasible.