Insights to flow induced vibrations in computer hard disks

Read/write operations in computer hard disk drives (HDD) are supported by a rotary actuator. Air movements in the drive are a consequence of still air dragged along by the flat surfaces of the spinning circular disks. Air flowing in the enclosed HDD induces severe mechanical vibration of the actuator that causes Track Mis-registration error (TMR) and limits the achievable TPI, an indicator of the storage capacity of a computer hard disk drive. The velocity fields of an enclosed HDD model were measured with a Laser Doppler Anemometer non-intrusively. The model retained most of the common dimensions and basic features of a 3 1/2 " HDD. The disks were spun at 10,000 rpm. From the spatial derivatives of the Reynolds shear stresses spatially distributed in the HDD model, the aerodynamic force distribution in the flow field was obtained. It was apparent that the highly fluctuating aerodynamic forces from the surrounding air acted on the arms and could have caused the tips of the arms to yaw back and forth. The aerodynamic action maybe closely related to the flow induced vibrations on arms widely reported by the hard disk drive industries. By modifying the cross sectional shape of the actuator arms, the attenuation of aerodynamic forces in the flow field was not observed.