Cooling Analysis of a Passenger Car Disk Brake 2009-01-3049

In the present paper, simulations of a cooling-down process of an automotive disk brake system during a constant drive condition are presented in comparison with experimental data. The simulated condition was chosen because of its considerable sensitivity to the convective heat transfer changes. Performed were simulations of the air flow pattern around a passenger car with fully resolved geometry details including a brake system with pin-shaped brake disks at constant air speed. Conduction and radiation effects were considered by a fully coupled simulation between flow and thermal codes. In CFD, wheel rotation has been taken into account via MRF modeling (= Multiple Reference Frame). A validation of the underlying methodology was recently carried out by comparing characteristic mean values of cooling-down times – which indicate cooling-down behavior – to experimental values obtained in the Thermal Wind Tunnel of Stuttgart University. Based on this methodology, a detailed analysis of the cooling process as well as the influence of some well-chosen parameter changes is presented. Compared to baseline geometry, flow field changes caused by changing parts in the wheel vicinity can be illustrated by the differential velocity pattern around the brake. The impact of a modified flow field pattern on surface heat transfer can be visualized by differential heat transfer coefficients. Investigations on in-vane flow and heat transfer are presented as well as the heat transfer subdivision into convection, radiation and conduction. Within this context, the radiation number c_R is introduced to simplify the calculation of the radiation fraction of the total heat transfer. Altogether, the presented analysis exemplifies how the underlying methodology can effectively support the thermal development process of vehicle disk brakes during early design stages.