Aerodynamic effect on natural frequency and flutter instability in rotating optical disks

Abstract

Experimental studies on the aerodynamic coupling effect on natural frequencies and flutter instability of rotating disks are investigated in this paper. The experiments performed using a vacuum chamber and optical disks give two main results. One is that the aerodynamic effect by surrounding air reduces the natural frequencies and critical speeds of the vibration modes in pre-flutter regions. The other is that the natural frequency of the disk rotating at ambient atmospheric pressure is equal to that in vacuum at the flutter onset speed where the disk experiences aero-induced flutter. In post-flutter regions, the aerodynamic coupling between the disk and surrounding air increases the natural frequencies of the disk. IntroductionDuring the past few years, optical data recording, together with magnetic data recording, has made a significant contribution to the development of information storage devices. Recent trends in optical disk drives are the transition from CD drives to high-density DVD drives, the spread of several rewritable disk drives and the development of new types of information storage devices (Lee and Kim, 1998). The demand for higher data transfer rate causes a dramatic increase of rotational speeds in CD-ROM drives. During the last three years the transfer rate of the CD-ROM drive was increased from 8 · (8 times the transfer rate of the original CD-ROM) to 52X drives. DVD-ROM drives recently repeat the same step of the speed increase.As the rotational speed increases, the backward natural frequency of a rotating disk decreases and vanishes at critical speed. At the critical speed, a stationary transverse force excites resonance and causes buckling instability in the rotating disk. A single backward traveling wave is excited at a certain speed above the critical speed. However, one of important issues to be considered for higher rotational speeds is aerodynamic flutter. The self-excited vibration can be induced by the aerodynamic effect around the rotating disk. Since Lennemann (1974) studied aerodynamic effect on rotating disk files, some researchers have studied the aerodynamically induced disk vibrations. Hosaka and Crandall (1992) and Huang and Mote (1995) have investigated the vibration stability of a flexible disk spinning very close to a rigid wall. In those papers, the classical hydrodynamic lubrication theory is applied by assuming that the Reynold's number of the fluid in the gap is very small. Recently, Kim et al. (2000) has predicted that the flutter speed of a hard disk drive can be about 35,000 rpm. Lee and Kim (2002) also observed the aero-induced flutter in optical disks. A modal extraction method to predict flutter of rotating disks was studied by the estimation of nonconservative aerodynamic pressures (Hansen et al., 2001).When a disk spins in open air without an enclosure, aerodynamic flutter occurs at lower speeds than the flutter speed for the disk spinning close to a rigid wall. It is because the nonsymmetric stiffness, generated by the radial component of airflow in the l...

Modal interactions in a rotating flexible disc

“…where x n = [· · · x m,n · · ·] T ,x n = [· · ·x m,n · · ·] T , x n = e −in tã n ,ã n = [· · ·ã m,n · · ·] T , Unlike the work performed by D'Angelo and Mote [3], Jia [6], Kim et al [13], and Lee et al [17,18], the present work remains the non-diagonal elements k n m 1 ,m 2 (m 1 = m 2 ) in matrix L n in equation (7) to consider the interaction between the modes possessing different numbers of nodal circles.…”

“…Thus, vibrations and linear stability of a rotating flexible disc coupled to the acoustic oscillations of the surrounding fluid were investigated theoretically and experimentally by Kim et al [13], Jana and Raman [14], and Kang and Raman [15,16]. For the rotating optical discs in CD and DVD drives, Lee et al [17,18] analysed the aerodynamic effect on the natural frequency and flutter instability. Kim and Renshaw [19] attempted to predict aeroelastic flutter of a rotating disc in an unbounded fluid.…”

“…The experimental results of D'Angelo and Mote [3] show that neglecting the modal interactions can cause evident error in analysing the frequency, and the maximum error obtained is 25.56 per cent, which is not acceptable for engineering. However, D'Angelo and Mote [3], Jia [6], Kim et al [13], and Lee et al [17,18] neglected the modal interactions when analysing the dynamics of rotating flexible discs. Therefore, it is practical and meaningful that the modal interaction is investigated to reduce the error in analysing the rotating flexible discs.…”

Nonlinear aeroelastic flutter phenomena of a flexible disk rotating in an unbounded fluid

“…Note that, although the specific details of the post-flutter response vary amongst different disks, they are quite repeatable for a particular disk. The current experimental observations are substantially more complicated than those previously reported (D'Angelo and Mote, 1993; Lee et al, 2003;Raman et al, 2002). The steel disks used in the current experiments have approximately half the diameter and 10-30% of the thickness of the steel disk used in the experiments of D'Angelo and Mote (1993) and Raman et al (2002).…”

Modal Analysis of Optical Disk Rotating at 15,000 rpm Close to a Rigid Wall

“…[2][3][4] High-speed rotating disk also causes aerodynamic effect. [5][6][7][8][9][10][11][12] Thus, it is important to suppress the vibrations and increase the natural frequencies of the rotating disk. 13,14) The narrow gap between the disk and the rigid wall effectively causes these variations in dynamic characteristics.…”