Performance evaluation of a micro gas turbine centrifugal compressor diffuser

Krige, David Schabort (2013-03)

Thesis (MScEng)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Micro gas turbines used in the aerospace industry require high performance with a compact frontal area. These micro gas turbines are often considered unattractive and at times impractical due to their poor fuel consumption and low cycle efficiency. This led to a joint effort to investigate and analyze the components of a particular micro gas turbine to determine potential geometry and performance improvements. The focus of this investigation is the radial vaned diffuser which forms part of a centrifugal compressor. The size of the diffuser is highly constrained by the compact gas turbine diameter. The micro gas turbine under consideration is the BMT 120 KS. The radial vaned diffuser is analyzed by means of 1-D and 3-D (CFD) analyses using CompAero and FINETM/Turbo respectively. The aim is to design a diffuser that maximizes the total-to-static pressure recovery and mass flow rate through the compressor with minimal flow losses. An experimental test facility was constructed and the numerical computations were validated against the experimental data. Three new diffusers were designed, each with a different vane geometry. The static-to-static pressure ratio over the radial diffuser was improved from 1.39 to 1.44 at a rotational speed of 120 krpm. The static pressure recovery coefficient was improved from 0.48 to 0.73 with a reduction in absolute Mach number from 0.47 to 0.22 at the radial diffuser discharge.

AFRIKAANSE OPSOMMING: Mikro-gasturbines wat in die lugvaart industrie gebruik word, vereis ‘n hoë werkverrigting met ‘n kompakte frontale area. Hierdie gasturbines word menigmaal onaantreklik geag weens swak brandstofverbruik en n lae siklus effektiewiteit. Dit het gelei tot ‘n gesamentlike projek om elke komponent van ‘n spesifieke mikro-gasturbine te analiseer en te verbeter. Die fokus van dié ondersoek is die radiale lem diffusor wat deel vorm van ‘n sentrifugaalkompressor. Die deursnee van die diffusor word deur die kompakte gasturbine diameter beperk. Die mikro gasturbine wat ondersoek word is die BMT 120 KS. Die radiale lem diffusor word geanaliseer deur middel van 1-D en 3-D (BVD) berekeninge met behulp van CompAero en FINETM/Turbo onderskeidelik. Die doelwit is om ‘n diffusor te ontwerp met ‘n verhoogde massavloei en drukverhouding oor die kompressor. ‘n Eksperimentele toetsfasiliteit is ingerig om toetse uit te voer en word gebruik om numeriese berekeninge te bevestig. Die staties-tot-stasiese drukstyging oor die radiale diffusor is verbeter van 1.39 tot 1.44 by ‘n omwentelingspoed van 120 kopm. Die statiese drukherwinningskoeffisiënt is verbeter van 0.48 tot 0.73 met ‘n vermindering in die absolute Machgetal vanaf 0.47 tot 0.22 by die radiale diffusor uitlaat.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/80119
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