Multi-fidelity simulation of aeroengine across wide operation range using auxiliary fully coupled method

Multi-fidelity simulations for the design point or equilibrium lines of aeroengines are implemented using fully coupled methods, simultaneously optimizing computational resources and speed. Fully coupled methods remove the requirement of characteristic maps by directly incorporating computational fluid dynamics models of subcomponents into the thermodynamic model of an aeroengine. However, poor convergence remains an urgent problem for fully coupled methods, particularly when performing multi-fidelity simulations in the near-boundary region. In response to this challenge, an auxiliary fully coupled method was developed in this study. This auxiliary method introduces a parametric priori knowledge and auxiliary coordinate transformations into the existing direct fully coupled method. An automated multi-fidelity simulation platform was established in-house and validated using the KJ66 turbojet engine. The simulation results of the equilibrium line were then compared with experimental data to validate the high accuracy and reliability of the multi-fidelity simulation. Moreover, two fundamental selection schemes for matching parameters (mass flow or static pressure, transferred between the computational fluid dynamics and thermodynamic models) were implemented and systematically compared. The results demonstrate that the adaptive selection of matching parameters extends the application of multi-fidelity simulations to a broader operation range. In addition, the auxiliary fully coupled method was applied to a multi-fidelity simulation of a wider operation range, such as an adjustable nozzle area and variable power extraction. It was also compared with the existing direct fully coupled method with respect to the stable convergence scope. For the mass-flow matching scheme, the maximum stable convergence scope of the direct method was extended from 105 % to 315 % by the auxiliary method. For the static-pressure matching scheme, the auxiliary method also broadened the maximum stable convergence scope of the direct method from 55 % to 190 %. The comparison reveals that the auxiliary fully coupled method exhibits a wider range of far-off-design conditions, including the near-boundary region.