An investigation of the effect of inlet-swirl on the flow through a micro-gas turbine combustion chamber

Basson, Chenelle (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.


ENGLISH ABSTRACT: Previous research on the BMT120-KS micro-gas turbine engine has revealed that there is a component of swirl present at the compressor outlet. The effect of this inlet swirl on the flow through a micro-gas turbine combustion chamber is unknown. This project investigated the influence of the inlet swirl on the mass flow distribution and flow structures within the combustion chamber. An axial or non-swirl flow case was used as a control with which the swirling flow cases could be compared. Computational Fluid Dynamics (CFD) was used to investigate the mass flow distributions and internal flow structures of both the axial and the swirling flow cases. The axial and swirling mass flow distributions were determined experimentally as well. In order to determine the mass flow distribution experimentally with the test rig available at Stellenbosch University, certain assumptions were made. One assumption was that the pressure drop across the liner of the combustion chamber was constant along the liner. It was found that the experimental results validated the numerical results, with no more than 1.5 % difference for most of the sets of holes. The assumption was validated for the outer liner. However, the pressure drop over the inner liner varied with as much as 178 Pa, proving the assumption invalid. The discovery that the assumption was incorrect indicated that the experimental method was not accurate for this combustion chamber. However, it was concluded that the experimental results validated the numerical results, due to the good correlation obtained for the outer liner. The conclusion was made that the flow structures obtained numerically were a fairly accurate representation of the physical flow phenomena. When comparing the swirling flow cases to the axial flow case it was found that inlet swirl had a negligible influence on the mass flow distribution, but did have a negative impact on the flow structures within the combustion chamber. The recirculation zones for the swirling flow cases were not as well defined as for the axial flow case. It is therefore advised that the combustion performance be analysed with inlet swirl, in order to evaluate the effect of inlet swirl on the performance of the combustion chamber.

AFRIKAANSE OPSOMMING: Reeds bestaande navorsing oor die BMT120-KS mikrogasturbine-enjin het aangedui dat daar dwarrelende vloei by die kompressoruitlaat voorkom. Geen navorsing is tot dusver onderneem om die effek van die dwarrelende vloei te ondersoek nie. Die invloed van dwarrelende inlaatvloei op die massavloeiverspreiding en vloeistrukture in die verbrandingskamer is ondersoek. ‘n Aksiale vloeigeval (of nie-dwarrelgeval) is as kontrole, waarmee die dwarrelende vloeigeval vergelyk kon word, gebruik. Numeriese vloeidinamika is gebruik om die massavloei-verspreiding en die interne vloeistrukture te bepaal. Die massavloeiverspreiding is ook eksperimenteel bepaal vir beide die aksiale en dwarrelende vloeigevalle. Sekere aannames is gemaak om die massavloei-verspreiding eksperimenteel te kon bepaal, met die fasiliteite beskikbaar by die Universiteit van Stellenbosch. Een van die aannames was dat die drukval oor die verbrandings kamer se wand konstant bly. Die eksperimentele resultate het die numeriese resultate bevestig, met verskille van kleiner as 1.5 % vir die massavloeiverspreiding vir meeste van die stelle gate. Die aanname is bevestig vir die buitewand van die verbrandingskamer, maar is vir die binnewand ongeldig bewys. Drukvalle oor die binnewand het met soveel as 178 Pa gewissel. Daarom is dit afgelei dat die eksperimentele metode wat gebruik is, nie akkuraat vir hierdie verbrandingkamer is nie. Die eksperimentele resultate bevestig wel die numeriese resultate as gevolg van die goeie korrelasie wat vir die buitewand verkry is. Dit het gelei tot die gevolgtrekking dat die vloeistrukture wat numeries voorspel is, wel ‘n akkurrate voorstelling van die fisiese vloeiverskynsels is. Daar is bevind dat die dwarrelende vloei ‘n onbeduidende invloed op die massavloei-verspreiding gehad het, maar dat dit wel ‘n beduidend negatiewe invloed op die vloeistrukture gehad het. Die dwarrelende vloei se hersirkulasiesones is nie so goed gedefinieer soos in die geval van die aksiale vloei nie. Dit word aanbeveel dat die verbrandingswerkverrigting ontleed word, met dwarrelende inlaatvloei, om soedoende die effek van die dwarrelende inlaatvloei op die werkverrigting van die verbrandingskamer te evalueer.

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