Validated CFD modelling of an air-cooled motor controller heatsink in electric sailplane applications

Abstract

This thesis presents a validated three-dimensional computational fluid dynamics (CFD) investigation of the air-cooled motor-controller heat sink used in electric sailplane applications, with specific focus on the JS3 RES system. The objective was to establish a reliable, certification-relevant simulation framework capable of accurately predicting thermal behaviour and supporting future design improvements.A conjugate heat transfer (CHT) approach was employed to capture the interactions between the heat sink, the integrated heat pipes, and the external fuselage airflow. Heat pipes were modelled as high-conductivity solid rods, providing a computationally efficient yet physically representative approximation of lateral heat spreading. Commercial CFD tools (STAR-CCM+) were used, with careful selection of material properties, boundary conditions, and solver settings to ensure model fidelity. Experimental validation was performed using instrumented ground tests, with air-density corrections applied to enable consistent comparison between measured and simulated temperatures. The results demonstrate that the CFD model reproduces the thermal behaviour with high accuracy, deviating by less than 1% across the entire verification range of a benchmark test. This deviation is smaller than those observed in both experimental measurements and comparable simulations performed in SimScale. It therefore falls well within the acceptable limits typically expected for validated CFD simulations when compared against theoretical results. Key findings include the influence of mesh resolution on numerical accuracy, the critical role of heat pipes in lateral heat transport, and the sensitivity of validation outcomes to sensor placement and experimental precision. Beyond the JS3 RES application, this work establishes a validated CFD baseline suitable for parametric and topological optimisation, targeted thermal design improvements, and the development of efficient cooling strategies for other small-scale electric aircraft systems. The methodology and results contribute to aerospace engineering by providing a reliable, simulation-driven approach for the design and evaluation of compact thermal management systems.