Studies on stability and dynamics of a swirling jet

The temporal instability and nonlinear evolution of the swirling jet near a nozzle exit are studied by both normal-mode method and three dimensional d irect numerical simulation (3D DNS),. It is found that the swirl enhances t he maximum linear growth rates for negative helical modes, while decreases the growth rate for axisymmetric mode. Numerical simulations show that the evolution in early stage is compared well with the linear stability theory. In nonlinear stage, the swirl promotes the breakup of 3D large scale organ ized structures in the flow into small eddies.