The structure evolution of flow pattern around a slender was calculated by numerical method. It was pointed that the development of slender vortices leads to the change of topological structure about cross flow, and a critical flow pattern will appear. A high-order singular point in this flowfield was analysed by differential equation qualitative theory. The index of the high-order singular is -3/2. The topological structure of this singular point is instable, so bifurcation will be occurred and the topological structure of flowfield will be changed by little disturbance. The 3-dimensional flow structure of the steady and symmetric vortices pattern around a slender was gained.
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