Flow Past Large Obstructions Between Corotating Disks in Fixed Cylindrical Enclosures

Abstract

Numerical calculations have been performed for isothermal, laminar, three-dimensional flow past one or two fixed obstructions radially aligned and symmetrically located between a pair of disks corotating in a fixed cylindrical enclosure. The single-obstruction cases respectively model the influence on the flow of (a) a magnetic head arm support and (b) an air lock. The dual-obstruction cases model the simultaneous presence of these two objects. The air lock produces an interdisk cross-stream plane blockage of 62 percent while the two head arm supports produce blockages of 31 percent and 62 percent, respectively. For the cases with the air lock and arm support simultaneously present, the circumferential angle between them is fixed to 40 or 80 deg. Velocity, pressure, shear stress and the disk torque coefficient are predicted mostly for a Reynolds number (Re =ΩR22/v) corresponding to 10,000, approximately, where R2 , Ω, and v are the disk radius, the disk angular velocity in rad/s, and the kinematic viscosity of air at 300 K, respectively. The calculations show that a large blockage significantly alters the interdisk flow characteristics by markedly raising the pressure ahead of an obstruction and accelerating the flow through the empty space around it. This induces a detached region of reversed flow ahead of the obstruction, quite distinct from that in its wake. The disk surface pressure distributions point to a potential source of dynamical instability in rotating disk flows with obstructions. By redefining the torque coefficient and Reynolds number to account for dual blockage effects the relationship between these two quantities generally follows the theoretical expression of Humphrey et al. (1992). It is shown that the bulk of the drag on an obstruction is form drag as opposed to friction drag.