Abstract:
The significance of fluid dynamics systems with well-separated length scales is discussed aiming to comprehend the interaction among primary physical mechanisms, as each scale is essential for reproducing and predicting large-scale phenomena. At first, particle clustering in laminar flows is explored, demonstrating and explaining particle accumulations in steady flows. This will lead to the identification of Finite-Size Coherent Structures, relying on global fluid transport, particle dynamics, and particle-boundary interaction.
The application of well-separated-scale flows to turbomachines is also examined, focusing on instabilities observed with flow rate variations. In particular, the impact of small radial gaps on the onset of rotating instabilities is discussed, highlighting their significance on operating conditions. The last example of fluid dynamics systems with well-separated length scales deals with the respiratory fluid mechanics of distal air-ways, analyzed to understand occlusions in bronchioles. The impact of mucus rheology and surfactant on liquid plug formation is detailed, emphasizing the importance of the mucus layer on gas exchange in the lungs. Finally, future research avenues in multiscale flows are briefly discussed.