A numerical model of instability in axisymmetric jets

The detailed flow fields associated with instability in axisymmetric jets are realized by numerical integration of the time-dependent Navier-Stokes equations. The mechanism of amplification of small disturbances is shown to be two-dimensional for a thin boundary layer profile and conclusions regarding three-dimensionality which have been inferred from recent models of axisymmetrical systems are clarified. The computed flow field is shown to be dominated by the large-scale vortex ring structure which has been observed experimentally. Although the wavelength of vortex shedding is found to be slightly variable owing to the randomness of the initial perturbation, the results are shown to agree closely with experiment.