In hypersonic aerothermodynamics, two practical questions matter immediately for assessing boundary layer transition: where it begins, and how long the flow remains transitional before fully turbulent heating is established.

A hypersonic boundary layer does not become turbulent through a single instability pathway.

Transition to turbulence in hypersonic boundary layers is not governed by a single mechanism.

Currently, Earth's orbit contains roughly 15,000 active satellites and over 50,000 trackable objects, including defunct satellites, rocket bodies, and fragmentation debris.

The trajectory of a hypersonic vehicle is often constrained by the integral and peak aerothermal loads experienced during flight.

Space missions often encounter hypersonic physics during the re-entry of interplanetary vehicles.

In hypersonic flight, the forebody shock system does not exist in isolation.

Panel methods are among the most practical low-fidelity tools in hypersonic aerodynamics, balancing simplicity with useful accuracy.

During Artemis I, localized Avcoat material deterioration raised questions about thermal margins and how the re-entry environment should be interpreted

Compression shocks are nature’s mechanism for changing the magnitude and direction of velocity in supersonic and hypersonic flows.

Low-fidelity, physics-based models are often viewed as preliminary tools — useful early, then replaced by higher-fidelity analysis.

In hypersonic reentry, the difference between a viable trajectory and a failed one is often dictated by stagnation heat flux.

Aerothermal loads ultimately define the operational limits of a hypersonic mission.

Last week, we explored the asymptotic behaviour of post-shock Mach number and density ratio, leading to an asymptotic unit Reynolds number at the boundary-layer edge.

This raises a natural question: what happens in a shock-free flow?

Mach 5 is generally considered the rough bound between supersonics and hypersonics. But why is it so?