Transient Conjugate Heat Transfer CFD Simulations of an Experimental Brake Rig: Focus on Modeling of Radiation and Rotation

Abstract

This master’s thesis investigates transient conjugate heat transfer CFD modeling of an experimental truck brake rig, with focus on how thermal radiation and brake rotation should be modeled for accurate and efficient temperature prediction. A numerical model of the rig was developed in Simcenter STAR-CCM+ and evaluated using two braking cycles: a short severe cycle and a longer cycle adapted from the Alpine descent test. Two approaches for modeling disc rotation were compared: Rigid Body Motion (RBM) and Convective Velocity Option (CVO). In addition, different implementations of surface-to-surface radiation were assessed in terms of temperature prediction and computational cost. The results show that radiation has a comparatively small influence during short braking events, but becomes more important in longer high-temperature cycles, where neglecting radiation leads to over-predicted brake temperatures. For RBM, radiation had to be modeled in the solid domain to ensure energy conservation, although this significantly increased computational cost. To mitigate this, a parameter sweep was conducted to optimize the radiation settings. By reducing the Patch/Face Proportion and the Number of Beams, the solver computational time was decreased by more than 14.8%. This optimization maintained a high level of accuracy, yielding a Root Mean Square Error below 0.5 for the predicted temperatures compared to the most computationally expensive baseline. The results also show that CVO predicts lower maximum temperatures than RBM due to numerical smearing, while average disc temperatures remain relatively close. However, CVO reduced computational time by about 84 to 86%, making it a worthy engineering compromise when simulation speed is important. Comparison with brake rig measurements showed that both approaches captured the overall temperature development during braking, but both under-predicted temperatures during cooling. The thesis concludes that radiation should be included in transient brake thermal simulations, especially for long-duration braking, and that CVO is a promising alternative to RBM while, balancing accuracy and efficiency.