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

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 (epsilon similar to 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 (beta) 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.