Kelvin-Helmholtz instability of hydrodynamic supersonic jets

In the framework of the theoretical modeling of astrophysical jets, we present the numerical simulations of the nonlinear development of the axisymmetric hydrodynamic Kelvin-Helmholtz (KH) instability of a cylindrical supersonic beam. In agreement with previous models, unstable perturbations evolve into a series of conical shocks, but the evolution of these configurations appear quite complex. In particular it has been found that the instability process evolves through three different regimes, almost independently of the physical parameters. Initially (linear phase) the amplitude of unstable perturbations grows, leading to the formation of shocks, which are spaced according to the wavelength of the fastest growing mode. Thence shocks evolve by increasing their strength, inflating the jet without affecting its collimation. In the last phase we find strong mixing between the jet and external medium, which leads finally to the total disruption of the jet. The astrophysical implications of these results are discussed, in particular is pointed out that the morphological (blobs) and mixing phenomena observed in most extragalactic and stellar jets could be associated with the onset of KH instability.