Aerodynamic characteristics of carriage arm equipped on hard magnetic disks

In order to study aerodynamic characteristics of a carriage arm equipped on hard disk drives, water tunnel tests with ten times enlarged models of an actual arm were conducted based on Reynolds number similitude, which allows the time scale of the phenomena about 1,300 times slower than that compared with the phenomena under actual operation condition in the air. In the tests, flow visualization around the arm model with fluorescent dye injection and laser-light sheet technique was carried out. Fluid dynamic drag, lift and torque on the model were also measured. The effects of the oncoming flow velocity and profile, the installation angle and position of the arm and the configuration of the trailing edge of the arm on the power spectral density of the fluid dynamic force were investigated. As a result, predominant spectrum peak, the Strouhal number of which is about 0.24, is found in the power spectral density of dynamic lift force on the arm. The flow visualization confirmed that the dynamic lift with the spectral peak originates from the alternating vortex shedding from the trailing edge of the arm. The peak rapidly decreases as the installation angle increases while the velocity profile of oncoming flow and the position of the arm in the gap direction have little effect on the peak component. Furthermore, it was demonstrated that the dynamic lift can be reduced by modification of trailing edge shape of the arm.