Evaluation of an air shroud for rotating disk vibration suppression

The growth trend of the recording density of hard disk drives (HDD) makes a demand for higher head positioning accuracy at faster disk rotation speed. However, the higher rotational speed of disk generates the greater flow induced vibration known as disk flutter, which causes the increase of the track misregistration (TMR). In this paper, air shroud is evaluated with numerical simulation and analytical results for disk vibration suppression. Firstly, the finite element model (FEM) for computational fluid dynamics (CFD) analysis based on the 3D Navier Stokes equations is built up for air shroud. The turbulence air flow velocity and the pressure distribution are simulated and evaluated for the air shroud with different opening. The parameters describing the air bearing function of the shroud, such as the stiffness and damping, are calculated based on the simulation results. It is found that with the decreasing of the shroud opening angle, the air flow has a more uniform flow pattern with higher bearing stiffness and better damping. The CFD simulation results also indicate that the bearing stiffness and damping of the air shroud can be further increased with smaller shroud-disk spacing of the air shroud. To evaluate the effectiveness of the air shroud on the disk vibration suppression, an analytical model based on disk rotary dynamics including the functional air bearing stiffness and bearing damping of the air shroud is developed. The analytical results demonstrate 15.8% suppression in disk vibration amplitude for the flutter vibration mode at resonance frequency 550 Hz, mainly by the damping effect of the air shroud