Fluid dynamics mechanism of disk flutter by measuring the pressure between disks

The mechanism of disk flutter excitation in hard disk drives was experimentally examined in terms of the fluid dynamics. The sensors for measuring the pressure between the rotating disks were used. It was found that there was correlation between the pressure fluctuation amplitude and the flutter amplitude and that the pressure fluctuation was strongly influenced by the rotational speed and the disk-to-shroud spacing, especially in the outer disk. The pressure fluctuation was caused mainly by the winding of the flow in the disk rotational direction. This winding of the flow produced a nonuniform pressure distribution and it led to flutter excitation force. The pressure fluctuation and the disk flutter can be decreased by reducing the disk-to-shroud spacing which restricts the winding of the flow.