Development of a mixed-flow compressor impeller for micro gas turbine application

Diener, Olaf Herbert Ferdinand (2016-03)

Thesis (MEng)--Stellenbosch Uniersity, 2016.

Thesis

ENGLISH ABSTRACT: This thesis details the development of a mixed-flow compressor impeller to be used in a micro gas turbine (MGT) delivering 600 N thrust. Today‟s unmanned aerial vehicles (UAVs) demand high thrust-to-weight ratios and low engine frontal area. This combination may be achieved using mixed-flow compressors. The initial mixed-flow compressor impeller design was obtained using a 1-dimensional turbomachinery layout tool. A multi-point optimization of the impeller aerodynamic performance was completed. Thereafter a mechanical optimization was conducted to reduce mechanical stresses in the impeller. A coupled aero-mechanical (multi-disciplinary) optimization was concluded with the purpose of increasing the choke limit and reducing stresses while conserving aero-performance. Finally, a modal analysis was conducted and the rotor Campbell diagram was analysed to identify potential resonant conditions. The optimization process was set up and controlled in an integrated environment that includes a 3-dimensional Navier-Stokes flow solver and a 3-dimensional finite element (FE) structural solver. An artificial neural network (ANN) was used to generate a response surface based on a database of performance and geometric information. A genetic algorithm (GA) was applied to the response surface for optimization. The overall optimization process achieved an increase in total-to-total pressure ratio of 30.6% compared to the initial design while the isentropic total-to-total efficiency was increased by 5% at design conditions. The choke limit of the initial design was improved meaningfully. These values were obtained while also decreasing the peak von Mises stress to 30% below the material yield limit. Recommendations were made regarding the structural surroundings of the compressor and the operating speeds based on the Campbell diagram. Keywords: micro gas turbine, mixed-flow compressor, multi-disciplinary optimization, Campbell diagram.

AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwikkeling van 'n gemengde-vloei kompressorrotor vir 'n mikrogasturbine wat 600 N dryfkrag lewer. Hedendaagse onbemande vliegtuie vereis 'n hoë dryfkrag-tot-gewig verhouding en 'n lae enjin frontale area. Hierdie kombinasie kan bereik word met behulp van gemengde-vloei kompressors. Die aanvanklike gemengde-vloei kompressorrotor-ontwerp is verkry deur 'n 1-dimensionale ontwerpskode. 'n Multi-punt optimering van die rotor se aerodinamiese vermoë is voltooi. Daarna is 'n meganiese optimering uitgevoer om spanning in die rotor te verminder. 'n Aero-meganiese (multidissiplinêre) optimering van die rotor is gedoen met die doel om die smoorperk te verhoog en die spanning te verminder, terwyl die aerodinamiese vermoë behoue bly. Laastens is 'n modale analise uitgevoer en die rotor se Campbell diagram geanaliseer om potensiële resonante toestande te identifiseer. Die optimeringsproses is opgestel en beheer in 'n geïntegreerde omgewing wat 3-dimensionale berekenings vloeidinamika en 3-dimensionale eindige element strukturele berekeninge uitvoer. 'n Kunsmatige neurale netwerk is gebruik om 'n reaksieoppervlakte te skep, gebaseer op 'n databasis van rotor vermoë en geometriese inligting. 'n Genetiese algoritme is toegepas op die reaksieoppervlakte vir die optimering. Die algehele optimeringsproses het 'n toename in die totaal-tot-totale drukverhouding van 30.6% in vergelyking met die aanvanklike ontwerp bereik, terwyl die isentropiese totaal-tot-totale benuttingsgraad verhoog was met 5%. Die smoorperk van die aanvanklike ontwerp is noemenswaardig verhoog. Hierdie waardes is behaal gesamentlik met die vermindering van die piek von Mises spanning tot 30% laer as die materiaal swiglimiet. Aanbevelings is gemaak ten opsigte van die strukturele omgewing van die kompressor en die bedryfspoed gebaseer op die resultate van die modale analise. Sleutelwoorde: mikrogasturbine, gemengde-vloei compressor, multidissiplinêre optimering, Campbell diagram

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98781
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