Transient Flow Caused by a Rotationally Decelerated Disk Enclosed in a Housing

Abstract

The transient flow caused by a rotationally decelerated disk enclosed in a housing is studied theoretically and experimentally, in order to determine the influence of non-steadiness on the flow at the stopping period of the disk. The main results obtained are as follows : During the whole deceleration period there exists, despite the deceleration-rate, a core region similar to that of the steady-state with uniformly decreasing tangential ve1ocity, and its flow pattern is well approximated by a forced vortex. This uniform deceleration of the core is mainly due to the secondary flow in the boundary layer while the disk speed is larger than the core velocity, and due to the radial outward flow induced in the core when the disk speed becomes smaller than the core velocity. The theoretical analysis based on the assumption of a forced vortex gives satisfactory results, though the steady-state characteristics of the boundary layer are used.