Nozzle model for equivalently simulating the dynamic characteristics of human exhalation clouds

Current airway models for simulating human expiratory cloud diffusion face challenges due to numerous difficult-to-define entry boundaries and unverified simplifications, potentially leading to inaccurate simulations of dynamic characteristics of exhaled clouds. To address this challenge, a nozzle geometry boundary structure is designed with inclined channels and a main channel containing an internal obstacle. The inclined channels primarily affect the vertical velocity of the cloud, while the obstacle in the main channel primarily influences the internal vortices, thereby impacting the diffusion of the exhalation cloud. The effects of the angle of inclined channels, obstacle length, and obstacle width on four key parameters characterizing cloud dispersion: penetration distance, area, upper angle, and lower angle, are assessed in this study. Bayesian optimization was employed based on the results of simulations involving various nozzle structures. Optimization results indicated that an inclined channel angle of 63.3 degrees, obstacle dimensions of 2.8 mm width, and 5.2 mm length yielded minimal deviation. Numerical simulations using these optimized parameters closely matched the human results captured by Schlieren, with an average deviation of within 8%, effectively simulating the dynamic characteristics of exhaled clouds. The nozzle model offers reliable geometry boundary conditions for numerical simulations of human exhalation, thereby minimizing discrepancies between simulations and experimental results.