Integration of Functional Mock-up Units into Digital Twins of Aircraft Thermal Management Systems

Abstract

Hybrid-electric regional aircraft require detailed thermal management digital twins to assess performance and feasibility while reducing physical test effort. The Functional Mock-Up Interface (FMI) enables partners to exchange subsystem models as Functional Mock-Up Units (FMUs) for gate-to-gate simulation while preserving intellectual property. However, FMU integration introduces numerical coupling challenges, interface overhead, and potential loss of accuracy depending on the integration method. Benchmarking against a DLR Thermofluid Stream (TFS) reference model showed that FMU-based co-simulation can significantly increase computational effort, specifically from 8 min up to 2.5 h. Control-based integration further implicates transient deviations due to filtering, although steady-state accuracy generally remains unchanged. Therefore, it is mandatory to evaluate and compare FMU integration strategies to show that digital twin performance targets remain achievable when design, solver settings, and filtering are only applied selectively and systematically. The results show clear design guidance: employ native fluid libraries when possible for speed and accuracy, use FMU paired with adapters and without filters for accuracy, and reserve filtering for numerical stabilization only. Using a control approach to integrate the FMU improves simulation speed compared to adapters but introduces a small error, which in turn reduces simulation accuracy.