Visualization and spatial evolution of streamwise vortices near the minor axis of an elliptical cone

The transition of the three-dimensional boundary layer is a fundamental problem that urgently needs to be solved in the design of aerobats, among which the instability of streamwise vortices is one of the important characteristics. An experimental study on the spatial evolution law of streamwise vortices near the minor axis of an elliptical cone is conducted under Mach 6 conditions. First, a method for measuring and image correction of streamwise vortices in the cross section based on nano-tracker-based planar laser scattering technology is established, by which fine flow field structures of the boundary layer in the cross section at different streamwise positions are obtained. At the same time, combined with the temperature-sensitive paint technology, the temperature distribution of the model surface is obtained. The spatial evolution law of streamwise vortices is comprehensively analyzed, and the following conclusions are drawn. There are steady crossflow vortices on both sides of the streamwise vortices, and the temperature variation characteristics of the low-temperature regions along the flow direction controlled by the two are consistent. The steady crossflow vortices will experience an increase in amplitude and instability as they develop in space, and there is a clear correlation between the instability of the streamwise vortices and the instability of the steady crossflow vortices. The instability of streamwise vortices initially manifests as the instability of the “shoulder” structure, and the fractal dimension of the outer contour of the flow vortices shows a clear increasing trend in the flow direction. The temperature curves, fine structure images of streamwise vortices, and fractal curves reflect a good agreement in the spatial evolution law of the streamwise vortices.