摘要
It is well known that the vorticityω=▽×u,where u is fluid velocity,has clear mathematic definition,but for viscous flow the definition of a vortex remains an open problem for long[1,2],which has now evolved to a big
It is well known that the vorticity ω = △× u, where u is fluid velocity, has clear mathematic definition, but for vis- cous flow the definition of a vortex remains an open prob- lem for long [1,2], which has now evolved to a big confusion after many ＂vortex identification criteria＂ （＂vortex criteria＂ for short） were proposed to identify various turbulent coher- ent structures observed experimentally and numerically. The present communication attempts to clarify this confusing situ- ation and provide a preliminary answer to the question： What is a vortex？1）
