Visualization of flow structures around a spherical cone with supersonic film cooling based on NPLS

In the Mach 3.8 wind tunnel, flow structures of different scales around a spherical cone with or without supersonic film cooling were studied via nano-tracer planar laser scattering (NPLS), which has a high spatiotemporal resolution. Lots of typical flow structures were visible clearly, such as shock wave, expansion fan, shear layer and turbulent boundary layer. The analysis of two NPLS images between 5 microseconds revealed the temporal evolution characteristic of flow structures. With matched pressure, structures like K-H vortices in the mixing layer were seen clearly in both flows. While no injection, the flow is similar to the supersonic flow over a backward-facing step and the structures are simpler and there is a longer laminar region. Large scale structures such as hairpin vortices are visualized. In addition, the results were compared in part with the schlieren images captured by others under the similar conditions.