The Integration of a Mixed-Flow Impeller with a Crossover Diffuser into the CAT250TJ Engine

Micro gas turbine (MGT) engines are gaining popularity in military applications and show significant potential for conversion to turboshaft configurations. While traditional MGT engines employ centrifugal impellers, this thesis investigates an alternative approach: implementing a mixed-flow impeller with a crossover diffuser into the CAT250TJ MGT engine. Over the past 15 years, compressor design research at Stellenbosch University has focused specifically on MGT engine applications. Previous studies revealed that diffuser design heavily influences overall compressor stage performance, prompting the selection of a new crossover diffuser configuration. Van Eck (2023) generated both the mixed-flow impeller and crossover diffuser designs used in this investigation. This project aims to evaluate the performance benefits of implementing a mixed-flow impeller and crossover diffuser, which necessitated modifications to several major engine subsystems. Numerical simulations - including computational fluid dynamics (CFD) in Ansys® Fluent® and cycle modeling in Flownex® - were performed, followed by successful experimental testing of the upgraded compressor stage within the CAT250TJ engine. At the design point, CFD simulations demonstrated a 14.10% improvement in total-to-total pressure ratio and a 12.17% increase in total-to-total isentropic efficiency relative to the GEN1 CAT250TJ compressor. Engine testing confirmed these performance gains, achieving a 12.21% increase in static thrust with a 9.61%reduction in thrust-specific fuel consumption (TSFC) at 115 000 RPM. Experimental total-to-static pressure ratio results showed strong correlation with CFD predictions. The Flownex® cycle model also closely predicted thrust trends at reduced rotational speeds. Although it under-predicted thrust near the design point, it still proved to be an effective system-level modeling tool. Overall, the study demonstrates the performance benefits of implementing a mixed-flow impeller and crossover diffuser in a micro gas turbine engine and supports the continued development of compressor designs for MGT applications.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Greyling, Barend Christiaan Bester

Advisors dc:contributor.advisor

• Van der Spuy, S. J.
• Van Eck, H.

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/136043

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/136043