Abstract: Full three-dimensional computational fluid dynamics (CFD) simulation of micro turbojet engines has the potential to reveal coupled interactions between the engine body and the external flow field, as well as among engine components. In this study, an integrated three-dimensional internal–external flow model is developed for a micro turbojet engine, encompassing the far-field domain, intake, compressor, combustor, turbine, and exhaust nozzle. Steady Reynolds-averaged Navier–Stokes (RANS) simulations incorporating two-phase combustion and shaft power balance are performed to obtain four equilibrium operating points spanning 40%–100% of the rated rotational speed. The results are compared with those obtained using a conventional decoupled component-matching method based on component characteristics and thermodynamic cycle analysis to assess differences in overall engine performance predictions. The results indicate that neglecting complex flow distortion transmission and intercomponent coupling in the conventional method leads to discrepancies in predicted performance. At 100% rated speed, the decoupled method yields relative differences of 2%–3% in compressor pressure ratio, compressor adiabatic efficiency, and turbine adiabatic efficiency, approximately 2.93% in mean combustor exit temperature, and more than 4% in engine thrust compared with the integrated coupled simulation. The integrated approach captures intercomponent flow phenomena, including swirl interactions between the diffuser and combustor, hot-streak transport from the combustor exit, and circumferential nonuniformity in fuel species concentration, providing useful insights for overall engine matching and design. Additional simulations under off-design conditions demonstrate the feasibility of the integrated approach for predicting engine aerothermal interactions and performance degradation boundaries under complex operating conditions.

Key words: Micro turbojet engine, Full three-dimensional CFD, Integrated internal and external flow, Component coupling, Component matching