VORTEX SOLITONS IN A ROTATING FLUID WITHIN A NONUNIFORM TUBE

For analyzing forced axisymmetric flow of a non-uniformly rotating, in viscid and incompressible fluid within a long tube of slowly varying r adius, a theoretical model called the forced Korteweg-de Vries (fKdV) equation with variable coefficients is derived to calculate the amplit ude function of the Stokes stream function. When the fluid system is p laced under forcing by axisymmetric disturbance steadily moving with a transcritical velocity, new numerical results of flow streamlines are presented to show that well-defined axisymmetrical recirculating eddi es can be periodically produced and sequentially emitted to radiate up stream of the disturbance, becoming permanent in form as a procession of vortex solitons. The Rankine vortex and the Burgers vortex are adop ted as two primary flows to exemplify this phenomenon and it is shown that flow with a highly centralized axial vorticity is more effective in producing upstream-radiating vortex solitons.