Is turbulent entrainment a large-scale or small-scale phenomenon? This research challenges the conventional view of turbulent entrainment as a large-scale process, presenting evidence that it is more frequently a small-scale phenomenon. Through turbulence simulations, the authors examined entrainment directly, tracking the growth of vorticity and concentration along fluid particle pathlines. The results indicate that growth occurs close to the turbulence boundary within small radial displacements, and in times shorter than local large-scale times. These observations lead to a model demonstrating that overall rates can be predicted by large-scale quantities, even if the process occurs at small scales, requiring a fixed relationship across scales as in fully developed turbulent flows. These findings suggest that while engulfment models can be successful for fully developed flows, they may not represent the more frequent process of turbulent entrainment. The study sheds light on the complexities of turbulent flows and offers a new perspective on the mechanisms driving entrainment.
Published in Physics of Fluids, this research aligns with the journal's focus on fluid dynamics and turbulence. The investigation into the characteristics of entrainment contributes to the journal's exploration of fundamental concepts in fluid mechanics. The citations reflect the paper's engagement with existing research in the field of turbulence and fluid dynamics.