This presentation synthesizes the existing knowledge of turbulent flows as they are affected by compressibility effects. A phenomenological description is emphasized, drawing from over 75 years of experiments, theoretical developments and, more recently, high-fidelity numerical simulations.
After a visual introduction of engineering applications and natural flows in which compressible turbulence and shock-turbulence interactions are most relevant, several key theoretical concepts are highlighted (Kovasznay mode decomposition; energy balance between internal and mean and turbulence kinetic energy; the distinction between inertia and compressibility effects; and multiple definitions of Mach numbers in relation to turbulence). The main challenges associated with the numerical simulation of flows involving shockwaves and turbulence are targeted next, with a high-level description of the most commonly used methods.
The core of the presentation follows, comprising a survey of compressibility effects on canonical turbulent flows, that are used as building blocks to our present understanding. Shock-free flows are targeted first, including mixing layers, boundary layers and homogenous isotropic turbulence. The occurrence of shocklets in the latter for sufficiently high turbulence Mach numbers naturally leads to the study of the second category of flows, involving shock-turbulence interactions, for which configurations both with and without the presence of walls are considered.
The last part of the presentation is devoted to hypersonics. The extreme conditions found in this flow regime are summarized. Emphasis is then placed on the topic of hypersonic boundary layer transition, with new, acoustic instability modes becoming dominant. Three different strategies to suppress such instability mechanisms avoiding the transition to turbulence are described.
The presentation concludes with a brief discussion of challenges and future outlook in the field.