A step beyond the tryptic of acoustic streaming

The path followed since Faraday’s first observations of acoustic streaming has led to a modern picture of this field as split into separate panels of a tryptic: standing acoustic waves in a channel with uniform background density, known as Rayleigh–Schlichting streaming, with stratified background density, known as baroclinic streaming, and acoustic waves progressing far from the walls under the shape of an attenuated beam, known as Eckart streaming. In their theoretical work, Mushthaq et al. (2025 J. Fluid Mech. 1017 , A32) describe in a single continuous parameter space both Rayleigh–Schlichting and baroclinic streaming, thus making a decisive step forward in the frontier between two of these panels. Dealing with a stratification of thermal origin, they identify the level of heating above which baroclinic streaming becomes of the same order of magnitude or greater than Rayleigh–Schlichting streaming. They also depict the major part played by the channel size to wavelength ratio in this problem. This work will be of great help in designing the next generation of experiments concerning acoustic streaming and acoustic management of heat transfer. It is of interest for engineering fields like microfluidics, electronics cooling and biomedical applications. It can also serve as an inspiring basis for academic works in which waves are crossed with stratification.