Rarefied aerodynamics begins where the classical continuum assumption starts losing validity.

In high-speed internal flows, compression is not achieved through a single normal shock.

Unlike external shock impingement, compression ramps introduce an interaction that is intrinsically coupled to geometry.

The interaction between an incident shock and a boundary layer is not restricted to hypersonic flows, but its consequences become significantly more severe as Mach number increases.

In hypersonic aerothermodynamics, boundary-layer transition control is not simply about delaying turbulence.

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.

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.

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

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?