Introduction to Control Volume Based Transient Thermal Limit 2020-01-0039

Advancement in modern aircraft with the development of more dynamic and efficient technologies has led to these technologies increasingly operated near or at their operation limits. More comprehensive analysis methods based on high-fidelity models co-simulated in an integrated environment are needed to support the full utilization of these advanced technologies. Furthermore, the additional information provided by these new analyses needs to be correlated with updates to traditional metrics and specifications. One such case is the thermal limit requirement that sets the upper bound on a thermal system temperature. Traditionally, this bound is defined based on steady-state conditions. However, advanced thermal management systems experience dynamic events where the temperature is not static and may violate steady-state requirements for brief periods of time. Due to the large thermal time constants for many components, such transient violations may not represent system failure and an understanding of transient temperature limits is beneficial. To meet this need, this paper introduces the transient thermal limit via control volume representation. Instead of a constant thermal limit, the transient thermal limit approach generates a dynamic temperature profile limit by representing the thermal system with a control volume and scaling the input temperature profile such that the control volume does not exceed the steady-state temperature limit. This simple approach is based on a physical representation that is customizable to each system and can dynamically adjust the limit based on system conditions. Additionally, this control volume transient temperature limit methodology was developed to minimize information sharing between proprietary systems. The details of this transient limit generation methodology will be reviewed in this paper and illustrated through application on an example thermal system.