Vortex solitons in a rotating fluid within a non-uniform tube

For analyzing forced axisymmetric flow of a non-uniformly rotating, inviscid and incompressible fluid within a long tube of slowly varying radius, a theoretical model called the forced Korteweg-de Vries (fKdV) equation with variable coefficients is derived to calculate the amplitude function of the Stokes stream function. When the fluid system is placed 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 eddies can be periodically produced and sequentially emitted to radiate upstream of the disturbance, becoming permanent in form as a procession of vortex solitons. The Rankine vortex and the Burgers vortex are adopted 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.