Influence of Steps on Hypersonic Boundary Layer Transition

The control of hypersonic boundary-layer transition not only helps to improve the flight efficiency and aerodyna-mic thermal protection capabilities of hypersonic vehicles, but also plays a certain role in optimizing the structural design of aerospace vehicles. In this paper, the influence of forward-facing step and backward-facing step on boundary-layer transition on a flared cone at zero angle of attack was studied at Ma=6 using PCB fast-response pressure sensors and infrared thermography. The nonlinear interactions between different disturbance waves in the boundary layer were obtained by cross-bicoherence analysis of the pulsating pressure results. The results show that both the forward-facing step and backward-facing step will accelerate the occurrence of boundary-layer transition, with the backward-facing step exhibiting a stronger effect in accelerating this transition compared to the forward-facing step. However, these steps do not change the transition scenario and the difference interactions between the second mode and its first harmonic play a dominant role over the entire transition process.