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The evolution of three-dimensional temporally evolving plane mixing layers under strong vortex disturbances is investigated by DNS method. The convective Mach number and the Reynolds number used is set to be 0.8 and 200. The isentropic vortex is chosen as the model for vortex disturbances. Three different directions of the vortex axis (streamwise, spanwise, and normal directions) are considered in the simulations. For comparison, the computation with linear unstable oblique waves as disturbances is also executed. The results show that in the case of the streamwise vortex disturbance, significant increase in vorticity thickness can be found only in the early stage of development. In the case of the normal vortex disturbance, a high growth rate of the plane mixing layer is kept all the time, while in the linear wave case saturation occurs in the later stage of the simulation and the vorticity thickness stops increasing further. In the case of the spanwise vortex disturbance, the flow is quite quiet and the vorticity thickness attains the lowest growth rate.