Abstract
In this paper, characteristics of disk flutter (natural frequency of disk modes, modal damping ratios, and modal excitation caused by flow) were studied by using a HDD filled with air, helium, and their mixture gas. In our experiments, amplitude of disk flutter decreased as the fraction of helium in the mixture gas increased but was not simply proportional to the gas density. This contradicts the general understanding that the amplitude of disk flutter is proportional to density of fluid in a HDD. Analysis of modal parameters showed disk flutter excitation varied with respect to the helium-air mixture ratio in the same manner as the disk flutter amplitude. From the behavior of the excitation factor, we categorized three regions on the basis of the gas density ratio, i.e., the ratio of gas density to air density in 1 atm. at room temperature: the transitional region is helium-rich, the critical region is mid-way between the other regions and the turbulent flow region is air-rich.
