Abstract
Keywords: disc brake, convective heat dissipation, CFD
The importance of brake cooling has long been recognised but the analyses were limited to the tools (experimental and theoretical) available at the time. Work published by Newcomb and Millner (1965-66) was very useful in understanding fundamentals of heat dissipation from road vehicle brakes. Limpert (1975) provided further information about disc brake cooling. This work was mainly concentrated on brakes installed on vehicles, whilst Sisson (1978) looked in more detail into actual brake designs and mechanisms of heat dissipation. With the development and application of Computational Fluid Dynamics (CFD) techniques, brake flow and heat dissipation studies become much more detailed. Numerous data could be obtained at low cost and suitable design modifications introduced in order to improve convective cooling. Papers published by Daudi (1999), Wallis et al. (2001), Voller (2003), Voller et al. (2003), Sakamoto (2004), Hongguang (2006), Tirovic and Galindo-Lopez (2006), Palmer et al. (2006) clearly demonstrate the advantages in using CFD for studying convective heat dissipation from disc brakes. It is interesting to point out that in addition to the optimisation of `known´ vane and channel patterns, new designs are also being created ( - US Patent 7,100,748 B2, 2006). Flow analysis within a wheel cavity and around the exposed wheel remains very complex, as discussed respectively by Axon et al. (1999) and Basara et al. (2000). The analysis of the flow through the ventilation channel of a brake disc and influence of different parameters on brake convective cooling is still to be investigated in more detail. This is vital in order to generate novel disc designs with improved heat dissipation characteristics.
The work presented in this paper looks initially at the `standard´ commercial vehicle (CV) disc brake with 30 straight radial vanes, as shown in Figure 1. The number of vanes is then altered, in order to better understand the influence on air flow and heat dissipation characteristics. Some initial investigation regarding the number of vanes was performed by Limpert (1975) and Sisson (1978), however they were only looking at global effects. In order to investigate this important design parameter further, two alternative disc designs were analysed, one with 45 vanes (50% more compared to the standard design) and the other with 20 vanes (1/3 less than the standard disc). Detailed characteristics for all three designs are given in Table 1. The intention is to look at the flow and heat dissipation patterns (distribution of convective heat transfer coefficient and average values) in order to better understand the mechanisms governing flow and heat transfer coefficient and ultimately establish a knowledge base for designing new discs. Such large variation in the number of vanes (20, 30 and 45, an increase of 50%) has been chosen deliberately in order to make the differences in flow and heat dissipation characteristics more pronounced. All results presented here are based on CFD analyses. A very comprehensive experimental validation was conducted but these results could not be included in this paper due to limited space available.