Production of streamwise vortexes in a turbulent boundary layer

The whole process of the production and the development of the streamwise vortexes are studied. By using the method of direct numerical simulation, the production of the streamwise vortexes and the process from quasi-2-dimensional coherent structures to 3-dimensional coherent structures in the wall region of a turbulent boundary layer are simulated. The initial values of the quasi-2-dimensional coherent structures in the wall region are obtained on the basis of the idea of resonant triad in the theory of hydrodynamic stability. The results show that due to the nonlinear interaction, the quasi 2-dimensional structures gradually grow to 3-dimensional structures; the streamwise vortexes and the hair-pin vortexes are produced in this process. And the results of the simulation agree well with the experimental results. The affects of the adverse gradient on the generation and the development of streamwise vortexes are also studied. With the adverse pressure gradient, the streamwise vortexes generates earlier, rise faster, the amplitude of the coherent structures grows faster, and the structures becomes more complicated, which means that adverse pressure gradient can actuate the coherent structure and the development of the streamwise vortexes.