Abstract Boundary layer transition is an important factor in the design process of hypersonic vehicles, and crossflow instability is a critical mode. In this paper, the traveling crossflow instability in a laminar boundary layer at Mach 6 is experimentally investigated. Experiments were performed over a 7${}^{\circ }$ half-angle cone at 6${}^{\circ }$ angle of attack, with the unit Reynolds number of $R{e}_{\infty }=5.75\times 10^6$ m${}^{-1}$. Flush-mounted fast-response pressure transducers and time-averaging temperature-sensitive paint were used to capture the traveling crossflow instability and the stationary crossflow instability, respectively. The traveling crossflow waves with characteristic frequencies between 10 and 25 kHz are detected in the planes with the azimuthal angle between 23${}^{\circ }$ and 143${}^{\circ }$ away from the leeward ray. The three-dimensional amplitude growth was obtained. In general, the amplitude growth of the traveling crossflow instability is roughly leeside-forward and windside-aft. Although the traveling crossflow instability grows earlier on the leeward side, it has a larger amplitude on the windward side. Compared with the stationary mode, the traveling mode grows faster and reaches the highest amplitude earlier. In addition, a high-frequency instability with characteristic frequencies between 100 and 200 kHz is observed. It may be the secondary instability of the traveling crossflow waves, but whether it is true or not needs further experimental and numerical studies.

Highlights • In a hypersonic flow, the three-dimensional growth of the traveling crossflow instability on a yawed cone was measured. • Compared with the stationary crossflow instability, the traveling crossflow instability grows faster and reaches the highest amplitude earlier. • A high-frequency instability with $f=$ 100–200 kHz was found, and it may be the secondary instability of the traveling crossflow waves.