Human lungs fluid mechanics: an overview of current modelling techniques

Fluid mechanics governs numerous physiological processes in the respiratory system, influencing airflow dynamics, particle transport and aerosol formation, airway stability, mucus transport, surfactant mechanics, and pulmonary oedema. Over the past decades, engineers, physicists, and biomedical scientists have developed a wide range of models to describe these processes across multiple spatial and temporal scales. This paper provides an integrated overview of current modelling techniques in pulmonary fluid mechanics, emphasizing the multiscale and multiphysics nature of the lung. After discussing the principal challenges in simulating the mechanics of human lungs, we review the hierarchy of modelling approaches, from first-principle continuum formulations to reduced-order and data-driven models. We then explore strategies for coupling these models and conclude with a perspective on future directions, including the need for benchmark cases and clinically robust indicators for model validation.