Three-dimensional transitions in a swirling jet impinging against a solid wall at moderate Reynolds numbers

摘要

We consider the three-dimensional structure of a q-vortex interacting with a solid surface perpendicular to its axis. We use a direct numerical simulation based on a potential vector formulation with a Fourier decomposition in azimuthal modes for a Reynolds number equal to 100. This method is specially suited for the study of the nonlinear stability of axially symmetric flows because one may follow the raising of the different nonaxisymmetric modes from numerical noise, their nonlinear development, and their nonlinear interactions. For the given Reynolds number we find that there exists several transitions as the swirl number is increased, including the development of nonaxisymmetric instabilities for different azimuthal modes, and the formation of a vortex breakdown bubble that turns the flow axisymmetric again. We analyze these transitions and characterize them as a function of the swirl number for different distances of the incoming vortex to the wall.