Insights and perspectives on entrainment and detrainment in natural stratified flows

The entrainment hypothesis, first introduced by Taylor and later refined by Turner, has been instrumental in elucidating the mechanisms by which turbulence engulfs ambient fluid. Although entrainment dynamics has been extensively analyzed in geophysical applications, detrainment, the expulsion of fluid from turbulent regions, has received comparatively less scrutiny. This review synthesizes the current understanding of entrainment and detrainment, emphasizing their role in natural and engineered flow systems. Particular attention is paid to recent investigations of detrainment in obstructed plane jets, where the presence of obstacles significantly modifies shear layer development, mixing efficiency, and scalar transport properties. A critical evaluation of the prevailing models and their inherent limitations is presented, along with prospective research directions aimed at enhancing predictive frameworks for applications such as sediment transport, pollutant dispersion, and atmospheric boundary layer modeling.