Browsing by Author "Van Eck, H"

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    The effect of a crossover diffuser configuration on the performance of a mixed flow compressor stage for a micro gas turbine engine.
    (Stellenbosch : Stellenbosch University, 2023-11) Van Eck, H; Van der Spuy, SJ; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Mixed flow compressor configurations have become increasingly popular for use in Micro Gas Turbine (MGT) engines. Mixed flow configurations have the advantage of smaller frontal areas while still attaining high pressure ratios from a single stage configuration. The performance of these compressors is largely influenced by the performance of the diffuser, which in turn is limited by inherent geometric restrictions. Research has shown that, compared to legacy diffuser configurations, crossover diffusers provide superior performance in such cases. It does however suffer from inferior operating ranges. This study investigates various crossover diffuser configurations aimed at expanding the operating range and increasing the performance of a mixed flow compressor stage of a MGT engine. To this end, three baseline test compressors, featuring single vane crossover diffusers, are designed using the MATLAB® based 1D Application (App) V2.0. The baseline compressors cover a wide range of design mass flow rates, rotational velocities, and impeller meridional exit angles (mixed flow angles). To evaluate the effect of diffuser configuration on compressor performance, the diffuser configurations of the baseline compressors aremodified, with the achieved performance being compared to that of the baseline configuration. Preliminary performance prediction results for all designs are provided by the 1D App V2.0, which is based on mean line loss model theory. These results are validated using NUMECA/Fine™ Turbo CFD software. Diffuser modifications include various unique single and tandem vane crossover diffuser configurations. A splitter vane configuration provides a marked increase in choke margin, albeit at a slightly reduced stall margin. A relative choke margin increase of up to 106% is observed. Tandem vane configuration evaluations include the investigation of relative vane length, as well as tangential shift of the second vane row relative to the first. A 75% relative tangential shift tandem configuration provides the best overall performance results, regardless of relative vane length. A tandem vane configuration with a reduced first vane row number (half) is proposed. It provides a relative choke margin increase of up to 155% compared to the baseline configuration. As a final validation, the findings of this study are tested on a real-world application. A compressor upgrade is proposed for the CAT250TJ – Gen1 MGT engine. A baseline single vane crossover diffuser and four additional modified vaned diffuser configurations are presented. An on-engine evaluation is conducted using GasTurb™ gas turbine modelling software. The baseline configuration provides a 10.74% static thrust increase compared to the Gen1 configuration at maximum operating conditions. Compared to the Gen1 configuration, a reduced first vane row number diffuser configuration display a design point performance increase of 7.18% and 6.27% for total-to-total efficiency and pressure ratio respectively. An operating margin increase of 9.8% compared to the baseline crossover diffuser is also achieved.