Experimental Investigation Of The Exhaled Flow Characteristics Using PIV

In recent year,respiratory infectious diseases have always broken out.And it has been reported that these infectious diseases are transmitted by tiny particles with a diameter smaller than 10 ?m,and these particle and can follow the airstream.Therefore human respiratory activities can be source of contaminant transmission in indoor environment,especially in small confined enclosed space,such as the aircraft cabin.Coughing and sneezing are considered to be high-risk behaviors for transmitting infectious diseases.However,human breathing are always ignored,and it is reported that some influenza viruses have also been found in human breathing.So it is very important to study the characteristic of the exhaled flow,to obtain the precise boundary condition and find the appropriate turbulent model for controlling transmission of respiratory infectious diseases.In this study,the breathing thermal manikin was used to represent a real human.The experiment was carried out in an enclosed experimental mockup,and TR PIV was used to measure the exhaled flow.To ensure the reliability of the breathing thermal manikin,the velocity at exit of the moth was measured by a hot-wire anemometer,and the exhaled air temperature at exit was also measured by a high frequency thermocouple.The experiment results was analyzed by phase-averaged method,the turbulent characteristic of the exhaled flow was analyzed.The main goal of this study was to obtain the precise boundary condition and validation data for the computational fluid dynamics(CFD)simulation,and to deepen the understanding of the exhaled flow to provide help for controlling the transmission of the respiratory infectious diseases.It was found that the breathing thermal manikin can simulate the breathing volume,breathing frequency of a real human,and the exhaled air temperature was also similar with that of a real human.The velocity profile was not plat in each phase of exhalation process and presented bell-shaped,while it is plat in each phase of inhalation process.In the initial phase,a mushroom-shaped flow arose,while some jet characteristics appeared in the middle phase,and the diffusion angle was about 21°.The breathing zone presented hemispheric.The effect of thermal buoyancy and thermal plume on the exhaled flow was analyzed that thermal plume and buoyancy promote the diffusion of contaminant in exhalation process,and the thermal plume promote air circulation in breathing zone.The distribution of vorticity and turbulence fluctuation was obtained in each phase.The turbulence fluctuation was very strong in the transition stage between exhalation and inhalation,and the turbulence fluctuation in the second period was stronger than that in first fluctuation.The turbulence fluctuation at exit can be used for CFD simulations.The normal turbulence fluctuation was smaller than the streamwise turbulence fluctuation,and the max of streamwise turbulence fluctuation was 34%,while it was 25% for the normal turbulence fluctuation.The evolution of the normal turbulence fluctuation lags behind the streamwise turbulence fluctuation.The flow characteristic was obtained when breathing in noses.Comparing two breathing pattern,the safe distance was 0.5 m through analysis in this paper.