Delaying hypersonic boundary layer transition using forward-facing step arrays: An experimental work

Our previous research has demonstrated that a single forward-facing step (FFS) could delay the hypersonic boundary layer transition on a cone [Xu et al., “Influences of steps on the hypersonic boundary-layer transition on a cone,” AIAA J. 59, 439–446 (2021)]. This paper aims to further this study by investigating the control effects of FFS arrays on the hypersonic boundary layer transition on a 7° half-angle sharp cone. Experiments are conducted in a Mach 6 wind tunnel using nano-tracer-based planar laser scattering techniques and high-frequency pressure sensors. Cases with smooth surfaces, single FFS, or FFS arrays with different spacing and step heights are studied for comparison. The results show that FFS arrays present a better performance on stabilizing the second mode wave and delaying the transition than a single FFS. Notably, the spacing and height between and of the steps also play an important role in the delay effect. For the cases studied, a better control effect can be achieved using FFS arrays spaced at a larger distance or with step height increasing along the flow direction. Moreover, FFS arrays could restabilize the second mode wave that has been amplified by the upstream backward-facing step.