Flow Behavior in Radial Vane Disk Brake Rotors at Low Rotational Speeds

Abstract

The flow behavior through the vented channel of a brake disk determines its thermal performance, viz. its resistance to brake fade, brake wear, thermal distortion, and thermal cracking. We present experimental results of the flow characteristics inside the vented channel of a radial vane brake rotor with a selected number of vanes (i.e., 18, 36, and 72) but constant porosity (ε ∼ 0.8) at low rotational speeds (i.e., 25 rpm ≤ N ≤ 400 rpm). Using bulk flow and velocity field mapping measurement techniques, we observed that increasing the number of vanes for a given rotational speed results in (i) the increase in the mass flow rate of the air pumped by the rotor, (ii) the reduction of inflow angle (β) becoming more closely aligned with the vanes, (iii) more uniformly distributed passage velocity profiles, and (iv) increased Rossby number. In addition, for a certain range of rotational speeds (i.e., 100 rpm ≤ N ≤ 400 rpm), we identified the biased development of streamwise secondary flow structures in the vented passages that only form on the inboard side of the rotor. This is due to the entry conditions where the incoming flow must transition sharply from the axial to the radial direction as air is drawn into the rotating channel. The biased secondary flow is likely to cause uneven cooling of the brake rotor, leading to thermal distortion. At lower rotational speeds (i.e., N < 100 rpm), the biased secondary flows transitions into a symmetric structure.

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

“…A linear dependence was observed between the volumetric flow rate ( Q ) and rotational speed ( n ) of the vented brake disc, which was consistent with the findings of many other studies. 2,3,8,14,32,33…”

“…They also adopted the Dittus–Boelter equation to estimate the passage Nu e and applied power b = 0.93, which is double the value of the one applied in equation (15) and demonstrated that Ω v,r corresponds to Re e 2 , which is apparent because the flow rate and radial velocity component increased linearly with rotational speed. Finally, they compared their results with those of prior studies conducted by Sisson, 39 Tirovic et al, 40 and McPhee and Johnson.…”

“…While straight 7-mm-high radial vanes were used in the original brake disc (type A), airfoil-shaped profiles were selected for prototype brake discs B and C to increase their pumping performance, because the mass flow rate of a coolant is favourable to convective heat transfer. The number of vanes was increased from 41 to 53 in brake disc prototype B to increase the contact surface between the cooling air and vanes and to improve the heat transfer, as reported by Atkins et al 2 Additionally, the height of the vanes was increased from 7 to 8 mm to maintain the vane passage flow area. Prototype C had thicker vanes to improve heat conduction from the friction surfaces towards the inside air stream and to improve heat distribution between the inboard and outboard rubbing discs and reduce thermal distortion (i.e.…”

“…Although the increased thermal storage of a solid disc is beneficial for single braking events, vented discs perform better during continuous braking. 2…”

Modeling and simulation of frictional disc/pad interface considering the effects of thermo-mechanical coupling

“…Belhocine and Ghazaly (2016) developed FE model of the whole disc brake assembly and validated by using experimental modal analysis. Atkins et al (2019) presented a particle image velocimetry flow measurement of air flow in the ventilation channels, thus cooling the disc down during braking operations.…”