Numerical simulations of the Kelvin-Helmholtz instability in radiatively cooled jets

We present the results of simulations of the development of the Kelvin-Helmholtz (KH) instability in a cooled, slab symmetric system. The parameters were chosen to approximate the physical conditions typically found in jets from young stellar objects (YSOs). The effect of different methods of maintaining the initial equilibrium were examined for varying density. In addition, the effect of adjusting the width of the shear layer between the jet and ambient material was studied and found not to have significant long-term effects on the development of the instability. We find that, in general, cooling acts to – increase the level of mixing between jet and ambient material through the ‘breaking’ of KH induced waves on the surface of the jet – increase the amount of momentum transferred from jet material to ambient material – increase the time taken for shocks to develop in the flow – reduce the strength of these shocks – reduce the rate of decollimation of momentum flux The first and second of these results appear to contradict the conclusions of Rossi et al. (1997) who carried out a similar study to ours but in cylindrical symmetry. It is found, however, that the differences between slab and cylindrical symmetry, while insignificant in the linear regime, explain the apparent discrepancy between our results and those of Rossi et al. (1997) in the non-linear regime.