單向固化中引發液柱對流之流力機制研究(2/3)
Date Issued
2003-07-31
Date
2003-07-31
Author(s)
DOI
912212E002073
Abstract
We investigate the stability of a binary alloy directionally solidifying at a
constant rate and rotating with spin and/or precession about an inclined axis. Results
show that, prior to the onset of instability, a flow is induced by inclination and
modified by rotation, having a velocity profile like a spiral Ekman flow. The induced
flow moves steadily relative to the system when the system rotates with precession
only, while it changes the direction periodically when the system rotates with spin (no
matter if precession is included). Based on this flow, the effects of inclined rotation on
the stability of the system are examined by linear analyses. We find that there are five
mechanisms affecting the stability due to inclined rotation: The reduction of buoyancy
and the rotation vector both along the height of the system are stabilizing, the gravity
component along the melt/solid interface is destabilizing, and the inclination-induced
flow and precession simultaneously play a stabilizing or a destabilizing role,
depending on their relative orientation and amplitude-ratio. In general, the
morphological mode is slightly stabilized whereas the convective and mixed modes
are significantly stabilized. In the case under inclined precession, the instability mode
moving aligned with the gravity component along the melt/solid interface is most
unstable. In the case under inclined spin, all the stability-affecting mechanisms act
equally in all directions so that the stability thresholds for the instability modes
moving in different directions are equal. For directional solidification applications,
present results suggest that to prevent compositional non-uniformities in the solid,
inclined spin is more effective than inclined precession.
Publisher
臺北市：國立臺灣大學應用力學研究所
Type
report
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