| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 97 === In the first part of this thesis, the interfacial instability of miscible magnetic fluids in a Hele-Shaw Cell is studied, experimentally and theoretically, with different magnitudes and incremental rates of magnetic field. The initial circular oil-based magnetic fluid drop is surrounded by the miscible fluid, diesel. The external uniform magnetic fields induce small fingerings around the initial circular interface, so called labyrinthine fingering instability caused by the magnetic dipolar forces.
It is shown that the lower magnetization and susceptibility of the magnetic fluid, the less the secondary waves around the interface that were dominated by the three-dimensional effects. At the beginning when the magnetic field is applied, the interfacial length grows fast. It then decreases when the magnetic fields reach the selected values, and finally approaches certain asympototic values. In addition, a dimensionless time parameter, , is defined as the ratio of the characteristic diffusion time to the characteristic magnetic time. The larger represents the stronger magnetic fields and the faster initial growth rate. The initial growth rate is directly proportional to . When is larger than 1000, the secondary wave appears. A correlation is found between the secondary wave length (λ) and the gap of the Hele-Shaw Cell (h): .
In the second part of this thesis, two fingering phenomena are observed in a rotating miscible Hele-Shaw cell flow: the large branching pattern which is caused by the centrifugal force and the small fingering pattern which is induced by the external magnetic field. Due to the diffusion, the concentration of the magnetic fluid around each small fingering is getting lower, and the magnetization is weaker, accordingly. Therefore, the Coriolis force becomes important and influences the small fingering pattern.
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