A coupled approach for vehicle brake cooling performance simulations

Advances of CFD methods together with the constant growth of computer capacity enables simulations of complex coupled fluid and thermal problems. One such problem is the evaluation of brake cooling performance. The brake system is a critical component for passenger vehicles and ensuring correct brake operation under all possible load scenarios is a safety issue. An accurate prediction of convection, conduction and radiation heat fluxes for such a complicated system is challenging from modelling as well as numerical efficiency perspectives. This study describes a simulation procedure developed to numerically predict brake system component temperatures during a downhill brake performance test. Such tests have stages of forced and natural convection, and therefore, the airflow is influenced by the temperature changes within the system. For the numerical simulation, a coupled approach is utilized by combining aerodynamic and thermal codes. The aerodynamic code computes the convective heat transfer using a fully-detailed vehicle model in the virtual wind tunnel. The thermal code then uses this data and combines it with conduction and radiation calculations to give an accurate prediction of the component temperatures, which are subsequently used for airflow recalculation. The procedure is described in considerable detail for most parts of the setup. The calculated temperature history results are validated against experimental data and show good agreement. The method allows detailed investigations of distribution and direction of the heat fluxes inside the system, and of how these fluxes are affected by changes in material properties as well as changes in parts within or outside the brake system. For instance, it is shown that convection and especially convection from the inner vanes is the main contributor for the heat dissipation from the brake disc. Finally, some examples of how changing the vehicle design affects the brake cooling performance are also discussed.