Axial oscillation of a magnetically levitated non-magnetic fluid column inside a straight magnetic pipe

The axial oscillation of a magnetically levitated non-magnetic liquid colum n in a magnetic fluid and a non-uniform weak magnetic field is studied theo retically and experimentally. The angular speed equation and wave speed equ ation of the interfacial wave are derived from the ferrohydrodynamics Navie r-Stokes equation in a given magnetic field by (1) omitting the non-linear terms, (2) assuming that the undisturbed interface between the levitated fl uid and the surrounding fluid is an infinite long cylindrical surface, and (3) assuming that the disturbance is an axisymmetric axial one of small amp litude. The experimental study is made by setting two very long permanent m agnetic north poles face to face with each other to form the non-uniform ma gnetic field, using silicon oil as the levitated fluid and using a diluted water-based magnetic fluid as the surrounding fluid. (C) 1999 The Japan Soc iety of Fluid Mechanics and Elsevier Science B.V. All rights reserved.