The reduction of air-borne noise in hard disk drive

An air-borne noise should occur when a platter (disk) is rotating under high rpm in hard disk drive. Here the air-borne noise includes not only an interaction between fluids itself, but also forced vibration of structures in contact with the flow. Nearly all problems of flow-generated noise, the energy source for sound production is some form of flow unsteadiness. An essential ingredient of flow unsteadiness is turbulence and vorticity. In this paper the thickness of Ekman boundary layer was analyzed, and with this theory a noise reduction was carried out by an optimized spacing between upper platter and cover housing.