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Optimisation of Pin Shape and Its Configuration for a "Pin" Type Vented Brake Disc Using CFD
Published October 22, 2006 by Society of Automotive Engineers of Japan in Japan
Judder may fall under the headings of cold or hot judder but by far the most complex to understand is hot judder. This may result from rotor deformation or an effect referred to as "hot spotting." It is clear that to minimize the occurrence of thermal judder it is necessary to avoid excessive heating of the rotor and at the same time avoid significant variation in temperature across the rotor. To this end the designer must ensure uniform heat dissipation from the rotor.
In high-performance braking applications vented discs are normally used as these provide a greater cooling surface. These discs increase cooling efficiency by employing braking surfaces (blades) separated by a number of "ribs" or "vanes" which allow air to pass between the two blades. To increase cooling efficiency some vented discs use pins to separate the braking surfaces as this arrangement increases the available area to dissipate the heat. The cooling efficiency of the brake discs depends on two parameters; the mass flow rate of air through the disc and the effective heat transfer coefficient on the surface of the disc blades and vent vanes/pins. "Pin" type vented discs have been found to be good at increasing heat transfer coefficient but mass flow rates through such discs are generally smaller when compared to vane type discs.
This paper attempts to define a plausible way of controlling the shape of the columns within a pin-vented disc with a view to finding an optimized configuration for a disc consisting of three rows of 36 "pins" positioned so that their center lines are separated by ten degrees, with the central row of pins offset by five degrees to the outer and inner rows. The optimization of this "pin" arrangement attempts to increase the average heat transfer coefficient and the wetted area in order to enhance the aero-thermal characteristics of the disc to increase heat dissipation from the rotor in a uniform manner and hence decrease the discs tendency to judder.
The results presented within clearly show the advantages of increasing the pumping efficiency of the brake rotor; this is demonstrated by the "high mass flow rate" design. It has also been shown that increasing the width of the second and third rows of pins produces a decrease in the flow rate through the disc whereas the first row has an optimal width that creates a venturi at the inlet which aids inlet velocities. A reasonable correlation has been demonstrated between the results from the computational fluid dynamic analysis and those gained from empirical formulas as well as previous computational studies.