Physical origin of vortex stretching and twisting: Viscous or inertial forces

In this paper, the physical origin of vortex stretching and twisting is theoretically investigated. The effects inertial viscous forces are mainly considered discussed. Two key conditions, i.e., solid walls three-dimensional (3D) disturbances, adopted in three typical cases. Among them, first two cases straight curved lines at initial time without any kind disturbance. third case a line with introduced 3D natural disturbances. Through experimental observations, numerical simulations, theoretical analysis these cases, illustrate that or still next time, respectively, regardless whether introduced. However, clearly shows once disturbances introduced, near stretched twisted by forces, instead typically demonstrated wake transition circular cylinder laminar boundary layer flat plate. Accordingly, based on definitions generation enhancement twisting, it confirmed conditions mechanism, while alone mechanism.