Flow behaviour in vented brake discs with straight and airfoil-shaped radial vanes

Abstract

This paper presents experimentally obtained flow characteristics inside the vane passage of a vented brake disc and at the brake disc exit. The flow conditions of three different brake discs were compared: a basic design with straight vanes and two prototypes with different vane heights, shapes (airfoil shape) and numbers. The possible effect on brake disc cooling performance was studies. Hot-wire anemometry was applied to measure the pumping performance of different discs, and particle imaging velocimetry was used to map the velocity field. All three discs were tested on a brake disc dynamometer according to the SAE J2522 standard, and the maximum temperature was measured during the thermal capacity test. No prototype outperformed the original brake disc. Moreover, the brake disc with the increased vane thickness and reduced vane height (prototype C) performed significantly worse, whereas prototype B, designed with an increased vane height and increased number of vanes, performed similarly to the original brake disc. A comparison of the flow characteristics of the three discs indicated that the significant decrease in the cooling airflow rate deteriorated the cooling performance of prototype C the most. On the other hand, the improved pumping performance did not improve the cooling performance of prototype B. Only the comparison of the internal cooling air flow pattern of the original and prototype B brake discs revealed the reason. While the characteristic jet-wake flow structure formed within the vane passage of the original brake disc, the inter-vane channel flow within brake disc B was distributed much more uniformly in a circumferential direction, with significantly lower flow velocities near the pressure vane side. This reduced the convective heat transfer on the brake disc vanes, which number, as well as the heat transfer surface area increased without the desired cooling effect.