The Experimental evaluation of a mixed-flow compressor impeller and cross-over diffuser.

[摘要] ENGLISH ABSTRACT: In the past decade Stellenbosch University has been actively involved in thedevelopment of components for Micro-gas turbines (MGTs). MGTs are particularlyattractive to the energy and defence sector due to their high thrust-toweightratio and thus relatively high power output. The use of a mixed-flowcompressor impeller is attractive for MGTs due to its mass flow vs pressure ratiocharacteristics. Previous researchers optimised and manufactured a mixedflowcompressor impeller and cross-over diffuser for this specific reason. Thegoal of this thesis is to experimentally validate the numerical predictions madefor the compressor stage with the computational fluid dynamics (CFD) codeNUMECA. Experimental tests were conducted with a compressor test benchin the Gas Dynamics Laboratory at Stellenbosch University. The air receivercapacity limited the operational speed of the facility to 50 000 rpm. Theperformance of the impeller is evaluated numerically and experimentally withboth a cross-over and vaneless diffuser. The effect of trailing edge blade tipclearance on the performance of the impeller is also investigated numericallyand experimentally. The assembly of the test bench allowed for design modificationsto be made to the shaft, bearing housing, split ring spacer and bearinglayout. The modifications proved beneficial as experimental tests were conductedsuccessfully at 50 000 rpm. The experimental results agreed well withthe numerical results with the vaneless diffuser assembly delivering a total-tototalpressure ratio of 1.57 with an efficiency of 71.0% at a mass flow rate of0.26 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. Theeffect 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 diffuserassembly. A trailing edge blade tip clearance of 0.2 mm was also achieved experimentally and proved to be feasible.

[发布机构] Stellenbosch University