Molecular dynamics simulation of a convergent–divergent nozzle – a nanoscale perspective

Computational fluid dynamics (CFD) is a powerful tool for analysing fluid flow, but struggles with micro- and nano-fluidic systems. Molecular dynamics (MD) simulations, on the other hand, effectively study nanoscale flows. This study presents a novel multi-scale analysis of water flow through ten geometrically similar sub-micron convergent–divergent nozzles, with the smallest throat diameter at 14.64 nanometres, highlighting the impact of geometric scaling on flow behaviour. It uniquely demonstrates how scaling down the nozzle alters velocity profiles and vortex formation, phenomena that are not captured by traditional CFD due to the absence of interatomic interactions. The work emphasises the limitations of continuum assumptions at the nanoscale and underscores the importance of incorporating molecular interactions to accurately predict slip conditions, density fluctuations and surface effects. By comparing MD and CFD results, the study advances understanding of nanoscale flow dynamics and proposes coupling these approaches for improved modelling of micro- and nano-fluidic systems. These insights are critical for the development of accurate nano-fluidic devices and systems.