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

[摘要] 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-linecode developed for the in-house analysis of these impellers. The objective for theimprovement of the code is to accurately predict the performance of both radialflow 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 areaof a MGT engine while maintaining a high pressure ratio and ensuring a highthrust-to-weight ratio. The use of mixed-flow impellers in MGTs are thus attractive.Although detailed aerodynamic design is normally based on two- andthree-dimensional viscous flow analysis, 1-D analysis with empirical work inputand loss models is the basis for most aerodynamic performance analyses. Using1-D mean-line flow analyses also allows the researcher to analyse multiple geometriesin a short time span, while only analysing the best performing geometrieswith 3-D Computational Fluid Dynamics (CFD). Two areas of the mean-line codewere identified for improvement. A new slip factor formulation taking both radialand axial flow components into account was implemented. Secondly, an alternativelocation for the inter-blade throat area was proposed, considering the areabetween a main blade and splitter blade, as opposed to the area close to the inducersection which is effectively between the main blades. The code was adaptedto calculate the throat parameters for the alternative location and two iterations. of the code were subsequently created. The first employing the new slip factor andthe second employing both the new slip factor and an alternative throat location.Three diferent impellers, of which one impeller is a mixed-flow impeller, wereanalysed 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 theperformance of the mixed-flow impeller reasonably well. The mean-line code overpredicted 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 pressureratio of the centrifugal impellers was under predicted on average by 15%, whilethe the isentropic efficiency was predicted within 3%. It was however found that ablade outlet angle of 90 adversely affected the performance prediction of the code.

[发布机构] Stellenbosch University