Performance analysis of a micro gas turbine engine using computational fluid dynamics

Date
2023-03
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH SUMMARY: Micro Gas Turbines (MGTs) are typically made up of a centrifugal compressor, combustor, axial turbine and exhaust nozzle combination. The aim of this thesis was to develop a complete numerical model of the CAT 250 TJ micro gas turbine in order to determine the operational performance characteristics of the engine. Computational Fluid Dynamics (CFD) was used to determine the operational requirements and the performance of the MGT compressor and turbine stages. The boundary conditions from these simulations were used to determine the required temperature gain over the combustor. A model of the combustor was developed that incorporated a combination of heat sources to emulate the energy release from combustion without modelling the physical combustion process directly. The use of these heat sources was found to provide an adequate temperature rise over the combustor region. A model containing the combustor, turbine stage and nozzle was then developed using conditions from the compressor outlet as the combustor inlet boundary condition. Experimental tests were performed using the same MGT to determine the performance parameters over the engines speed range. These performance parameters were compared to the simulated engine performance. It was found that at the design speed of 115 000 rpm, the simulated thrust and mass flow rate was 0.7% and 2.67% lower than the corrected experimental values at this speed. It was found that the use of these heat sources provide an approximate temperature distribution within the MGT and can be used to model the overall engine performance. An obvious next step would be to improve the modelling of the combustion process, in order to obtain a more accurate temperature distribution within the engine.
AFRIKAANSE OPSOMMING: Mikro gasturbine enjins (MGTs) bestaan tipies uit ’n sentrifugaal kompressor, verbrander, aksiale turbine en uitlaatmondstuk kombinasie. Die doel van hierdie tesis was om ’n volledige numeriese model van die CAT 250 TJ mikrogasturbine te ontwikkel om die operasionele werkverrigting-eienskappe van die enjin te bepaal. Berekenings Vloeimeganika (BVM) is gebruik om die operasionele vereistes en die werkverrigting van die MGT-kompressor en turbine te bepaal. Die grenstoestande van hierdie simulasies is gebruik om die vereiste temperatuurtoename oor die verbrander te bepaal. ’n Model van die verbrander is ontwikkel wat ’n kombinasie van hittebronne ingesluit het om die energievrystelling van verbranding na te boots, sonder om die fisiese verbrandingsproses direk te modelleer. Daar is gevind dat die gebruik van hierdie hittebronne ’n voldoende temperatuurstyging oor die verbrandingsgebied gee. ’n Model wat die verbrander, turbine en mondstuk bevat, is toe ontwikkel deur toestande vanaf die kompressoruitlaat as die verbranderinlaatgrenstoestand te gebruik. Eksperimentele toetse is uitgevoer met dieselfde MGT om die werkverrigtingparameters oor die enjin se spoedreeks te bepaal. Hierdie werkverrigtingparameters is vergelyk met die gesimuleerde enjinwerkverrigting. Daar is gevind dat by die ontwerpspoed van 115 000 rpm, die gesimuleerde stukrag en massavloeitempo 0.7% en 2.67% laer was as die gekorrigeerde eksperimentele waardes by hierdie spoed. Daar is gevind dat die gebruik van hierdie hittebronne ’n benaderde temperatuurverspreiding binne die MGT verskaf en gebruik kan word om die algehele enjinverrigting te modelleer. ’n Voor-die-hand-liggende volgende stap sal wees om die modellering van die verbrandingsproses te verbeter, om ’n meer akkurate temperatuurverspreiding binne die enjin te verkry.
Description
Thesis (MEng) -- Stellenbosch University, 2023.
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