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

Swanepoel, Pieter Coenraad (2018-12)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Deur die loop van die laaste dekade was die Universiteit van Stellenbosch betrokke by die ontwikkeling van komponente vir Mikro-Gas turbines (MGTs). MGTs is besonder aantreklik vir die Energie- en Verdedigingsektore a.g.v. hulle hoë energiedigtheid-teenoor-massa verhouding. Die gebruik van ’n gemengde vloei kompressor stuwer word aantreklik gevind vir applikasie in MGTs oor hul hoë drukverhouding karakter eienskappe. Vorige studente het om die rede onderskeidelik ’n gemengde vloei kompressorstuwer en oorgangsdiffusor ontwerp en vervaardig. Die doel van die tesis is om die numeriese voorpellings wat deur die Numeriese Vloei Dinamika (NVD) pakket NUMECA voorspel is eksperimenteel te bevestig. The eksperimentele toetse was gedoen op ’n kompressor toetsbank in die Gas Dinamika Labortorium by die Universiteit van Stellenbosch. Die lug voorsienings tenk het ’n beperkte kapasiteit en dus was die maksimum toets-spoed 50 000 opm. Die werksverigting en benuttingsgraad van die stuwer word numeries en eksperimenteel ge-evalueer met ’n oorgangs en ’n oop-kanaal diffusor. Die effek van lempuntspeling op die werksverigting en benuttinggraad van die kompressor word numeries en eksperimenteel ondersoek. Veranderinge aan die as, laer-huis, ring-spasie houer en laer uitleg was ook toegelaat. Die eperimente was suksesvol voltooi by 50 000 opm en dus het die ontwerp gebaat by die veranderinge. Die eksperimentele resultate stem goed ooreen met die numeriese resultate met die oop-kanaal diffusor opstelling wat n totaal-tot-totaal drukverhouding van 1.57 met ’n benuttingsgraad van 71% by ’n massavloei van 0.26 kg=s gelewer het. Die oorgangsdiffusor opstelling het n totaal-tot-totaal drukverhouding van 1.63 met ’n benuttingsgraad van 76% by ’n massavloei van 0.3 kg=s gelewer. Daar was n beduidende effek op die stuwer se benuttingsgraad a.g.v. die verandering in lempuntspeling waarneembaar by die oorgangsdiffusor opstelling, maar die effek was nie waarneembaar by die oop-kanaal diffusor opstelling nie. ’n Lempuntspeling van 0.2 mm was eksperimenteel behaal en bewys as haalbaar.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105073
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