Visualization study on the flow structures in the transitional boundary layer under an adverse pressure gradient

By using hydrogen bubble time-line method, the characteristics and evolution of flow structures in an excited transitional boundary layer under an adverse pressure gradient were studied. In the experiments, a digital indicator was used, by which the visualization results of plan view and side view at different position can be analyzed coherently at the same phase of the induced perturbation. Besides the T-S wave and hair-pin vortex which is typical in the transitional boundary layer, the results highlights some important detail phenomena and mechanisms of the re-generation of second hair-pin vortices, the appearance of multiple streamwise vortices, as well as the initial flow breakdown.