Experimental study on nozzle design for equivalently simulate the changing characteristics of human exhalation clouds

This paper addresses the issue of current human exhalation models being unable to simulate the changing process of human exhalation clouds equivalently. To solve this problem, we utilize the Schlieren technique to observe the changes of human exhalation clouds and design a nozzle model that can simulate the changing characteristics of these clouds. The nozzle is designed with a multi-channel structure, mainly with a main channel and upper and lower inclined channels. The flow and inclination angles of the upper and lower inclined channels significantly affect the final cloud characteristics. In contrast, the mixing clouds of the main and inclined channels greatly impact the diffusion rate of the final clouds. By adjusting the exit width of the inclined channel to 2 mm and the inclination angles of the inclined channels to 62.5 degrees, we can ensure that the average deviation of each of the four selected parameters used to characterize the cloud characteristic is within 10 % at the full moment of exhalation, effectively simulating the changing characteristics of human exhalation clouds. This nozzle model can improve experimental realism for exhaling and provide accurate boundary conditions for computational fluid dynamics simulations.