Analysing the performance of a compressor impeller for a micro gas turbine

Bindeman, Marco (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: This project sets out to numerically evaluate the performance of micro gas turbine (MGT) compressor impellers and to improve the 1-Dimensional (1-D) mean-line code developed for the in-house analysis of these impellers. The objective for the improvement of the code is to accurately predict the performance of both radial flow and mixed-flow impellers. The possible applications for MGTs are numerous. They find specific application for the propulsion of unmanned aerial vehicles (UAVs). Mixed-flow compressors offer the opportunity to reduce the frontal area of a MGT engine while maintaining a high pressure ratio and ensuring a high thrust-to-weight ratio. The use of mixed-flow impellers in MGTs are thus attractive. Although detailed aerodynamic design is normally based on two- and three-dimensional viscous flow analysis, 1-D analysis with empirical work input and loss models is the basis for most aerodynamic performance analyses. Using 1-D mean-line flow analyses also allows the researcher to analyse multiple geometries in a short time span, while only analysing the best performing geometries with 3-D Computational Fluid Dynamics (CFD). Two areas of the mean-line code were identified for improvement. A new slip factor formulation taking both radial and axial flow components into account was implemented. Secondly, an alternative location for the inter-blade throat area was proposed, considering the area between a main blade and splitter blade, as opposed to the area close to the inducer section which is effectively between the main blades. The code was adapted to calculate the throat parameters for the alternative location and two iterations. of the code were subsequently created. The first employing the new slip factor and the second employing both the new slip factor and an alternative throat location. Three diferent impellers, of which one impeller is a mixed-flow impeller, were analysed using the adapted mean-line code and the results were validated with 3- dimensional CFD. The newly adapted 1-D mean-line code was found to predict the performance of the mixed-flow impeller reasonably well. The mean-line code over predicted both the pressure ratio and isentropic efficiency (total-to-total) by 1.6% and 2.8% respectively, while also predicting a larger operating range. The pressure ratio of the centrifugal impellers was under predicted on average by 15%, while the the isentropic efficiency was predicted within 3%. It was however found that a blade outlet angle of 90 adversely affected the performance prediction of the code.

AFRIKAANSE OPSOMMING: Hierdie projek beoog om numeries die prestasie van mikro-gasturbine kompressors rotor te evalueer, asook die 1-dimensionele (1-D) werkverrigting-berekeningskode wat ontwikkel is vir 'n interne analise van die rotors. Die mikpunt van die verbeterde kode is om die prestasie van die radiale vloei en die gemengde-vloei rotors akkuraat te voorspel. Daar is vele moontlike toepassings vir mikro-gasturbines. Mikro-gasturbines kan spesifiek gebruik word vir die aandrywing van onbemande vliegtuie. Gemengde-vloei kompressors bied die geleentheid om die voorste area van 'n mikro-gasturbine-enjin te verklein, terwyl dit 'n hoë drukverhouding en 'n dryfkrag-tot-gewig verhouding behou. Die gebruik van gemengde-vloei rotors in mikro-gasturbines is dus aanloklik. Al is gedetailleerde aërodinamiese ontwerpe gewoonlik gebaseer op 2- of 3-dimensionele viskeuse vloei-analise, is 1- dimensionele analises met empiriese werksinsette en werksuitsette se modelle die basis vir die meeste aërodinamiese prestasie-analises. Deur die 1-D werkverrigtingberekeningvloei analise te gebruik, kan die navorser ook meervoudige geometrieë analiseer in 'n kort tydperk, deur slegs die hoogs presterende geometrieë te analiseer met 3-D berekenings vloeidinamika. Twee areas van die werkverrigtingberekeningskode is geïdentifiseer om te verbeter. 'n Nuwe glipfaktor formulering, wat beide die radiale en die aksiale vloei komponente in ag neem, is geïmplementeer. Tweedens is 'n alternatiewe posisie vir die inter-lem keëlarea voorgestel, wat die area tussen die hoof lem en die sekondêre lem in ag neem, eerder as die area naby die inlaat wat effektief tussen die hooflemme is. Die kode is aangepas om die keëlparameters te bereken vir die alternatiewe posisie en twee iterasies van die kode is vervolgens geskep. Die eerste een is die toepassing van die nuwe glipfaktor en tweede, die toepassing van beide die nuwe glipfaktor en 'n alternatiewe keëlposisie. Drie verskillende rotors, waarvan een 'n gemengde-vloei rotor was, is geanaliseer deur die aangepaste werkverrigting-berekeningskode te gebruik en die resultate is gevalideer met 3-dimensionele berekenings vloeidinamika. Die nuut aangepaste 1-D werkverrigting-berekeningskode het bevind dat die voorspelling van die gemengde-vloei rotors se prestasie, redelik goed is. Die werkverrigtingberekeningskode het beide die drukverhouding en die isentropiese doeltreffendheid (totaal-tot-totale) met 1,6% en 2,8% afsonderlik oorskat, terwyl dit ook 'n groter werksbestek voorspel het. Die drukverhouding van die sentrifugale rotors was onderskat met 'n gemiddelde 15%, terwyl die isentropiese doeltreffendheid voorspel was binne 3%. Dit is wel bevind, dat die lem se uitlaathoek van 90 'n nadelige effek op die prestasievoorspelling van die kode het.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106209
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