|Title:||Instabilities in directional solidification under inclined rotation||Authors:||Chung, C.A.
|Issue Date:||2003||Publisher:||臺北市:國立臺灣大學應用力學研究所||Start page/Pages:||381-408||Source:||Journal of Fluid Mechanics||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 the inclination and modified by the
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 direction periodically when the system rotates with spin (even 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 both buoyancy and the
rotation vector 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 combine to 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. For
inclined precession, the instability mode moving aligned with the gravity component
along the melt/solid interface is most unstable. For inclined spin, all the stabilityaffecting
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, the present results suggest that to prevent compositional
non-uniformities in the solid, inclined spin is more effective than inclined precession.
|Appears in Collections:||應用力學研究所|
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