The following images are results from a validation test of a vortex dynamics and acoustics code VINO. They show the evolution of the shear layer of a periodic jet under an axisymmetric perturbation. Time goes from left to right in each row with the upper images showing the shape of the vortex sheet and the lower showing a section through the shear layer. The shear layer is modelled as a superposition of finite-thickness filaments which interact via a modified Biot-Savart law. The images of the shear layer show only one filament in four, for clarity. Note how the vortex sheet is beginning to roll up into a ring, with the vorticity in one end of the sheet being depleted. The filaments look quite coarse since only a small number of control points are used to define the shape: this is valid because of the Fourier interpolation used to calculate the filament positions.
The basic parameters of the calculations are those of Martin & Meiburg, Numerical investigation of three-dimensionally evolving jets subject to axisymmetric and azimuthal perturbations, J. Fluid Mech., 230:271--318, 1991.
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