On the Flow between a pair of Corotating Disks in a Cylindrical Enclosure
Date Issued
2006
Date
2006
Author(s)
Tsai, Yuan-Sen
DOI
zh-TW
Abstract
This paper presents the measurements of the flow in the space between a pair of corotating disks. The present effort seeks to investigate the flow behavior and the mechanism responsible for it. Flow visualization techniques were employed to observe the flow structure, and detect its variations with parameters. Moreover, the typical high-speed flow was quantitatively measured using Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV). LDV gave the time history of velocity for power spectral analysis, whose results were used to understand the periodicity of flow. Based on the time period information, the phase resolved PIV measurements were conducted.
Flow visualization experiments conducted in the range of Reynolds numbers from to and of the disk spacing from to showed that, the flow may present three different regimes in accordance with the change of the value of (Re, S) pair. With low and small , a pair of circumferentially aligned vortex pair showing symmetry with respect the inter-disk mid-plane appears near the shroud. As increases or enlarges, the symmetry of this vortex pair breaks. Within the transition between the two foresaid regimes, the vortex pair shows shift-and-reflect symmetry.
Phase-resolved PIV measurements on the typical high-speed flow ( ) revealed that the instantaneous circumferential velocity oscillates periodically on both radial sides of the mid-point between the hub and the shroud, but in opposite trends. The oscillating amplitudes at different radial locations correspond to the radial profile of power spectral intensity. This is the first case which quantitatively presents the velocity variations in the flow region near the hub.
The analysis on the time-series vorticity field deduced that the symmetry breaking of circumferentially aligned vortex pair leads to the disturbances in the radial direction. As a result, a chain of alternating negative and positive periodic fluctuating vorticity foci occur around a circle, where the mean circumferential velocity achieves the maximum, and cause the clockwise and counter-clockwise fluctuating vortices respectively. The fluctuating vortices maintain their rotations by accumulating the axially aligned vorticity acquired as the fluids pass through the shroud boundary layer, and induce the radial (circumferential) gradient of the circumferential (radial) velocity around their centers. In the rotating reference frame, the resulting velocity patterns form the axially aligned vortical structures. The periodic Reynolds stress fields are responsible for the self-rotation of the fluctuating vortices, and emphasize the periodicity of the flow. The whole-field stress patterns may serve as the reference for numerical simulation.
Subjects
PIV
LDV
同步旋轉圓盤
相位解析量測
corotating disks
phase resolved measurement
Type
thesis
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