Browsing by Author "Burger, Christiaan Johannes"
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- ItemDesign procedure of a compact crossover diffuser for micro gas turbine application(Stellenbosch : Stellenbosch University, 2016-03) Burger, Christiaan Johannes; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: The design of a compact crossover diffuser to replace the size-limited radial diffuser and axial de-swirl cascade of the BMT120KS MGT is discussed. A crossover diffuser strives to combine the performance of a channel diffuser with the operating range and efficiency of a vaneless diffuser. Continuous aerodynamic vanes are designed to match the centrifugal impeller discharge flow and gradually diffuse the air towards the axial combustor inlet where the effect of swirling flow on combustor performance is experimentally investigated. Swirling combustor flow promotes combustion intensity, reduces combustion length, and enhances combustion stability. The study includes the development of a one-dimensional Mean-Line Code (MLC) which aids the designer in preliminary design and performance evaluation. A three-dimensional multiple operating point optimisation is conducted thereafter using Numeca FineTM/Turbo). The final design is manufactured using a five-axis CNC milling machine and experimentally tested by modifying the existing BMT120KS engine. The optimised crossover diffuser and modified impeller yielded a numerical increase in the total-to-static compressor stage pressure ratio from 2:93 to 3:83, increase in the static pressure recovery coefficient from 50:92% to 68:49%, and relaxed the compressor stage discharge flow angle from 84:14° to 34:28° (compared to the modified BMT120KS engine). Experimental results are recorded up to a rotational speed of 106 000RPM and extrapolated to the design speed of 120 000 RPM. The extrapolated results indicate a thrust increase from 107:3N to 220N and increase in total-to-static compressor stage pressure ratio from 2:62 to 3:65 at 120 000RPM (compared to the original BMT120KS engine).