Experimental Study On Characteristics Of The Jet Flow From An Aircraft Gasper

With the development of technology and the scale of the civil aviation expending,more and more people are traveling by airplanes for it can provide high speed and efficient public transport service.However,the current aircraft cabin air quality is not good enough,resulting in some problems of occupant safety,healthy and comfortable.Therefore,it is crucial to better understanding the reasonableness of cabin air distribution and creating a safe,healthy and comfortable airliner cabin environment,then improve the design of ventilation system and guarantee the safe,health and comfort of passengers and crew.Air distribution systems in current airliners are mainly divided into mixing ventilation and personalized ventilation.The mixing ventilation can create a stable airflow field but the supplied clean air reaches the passengers after mixing with the polluted(re-circulated)air.As a supplement,a passenger can turn on the gasper that delivers fresh air directly to the breathing zone and improve his thermal comfort.However,most studies focused on the flow field created by diffusers but ignored that created by gaspers.The objective of this study is to conduct experimental measurement and theoretical analysis of the characteristics of the jet flow from an aircraft gasper.The experimental system of personalized ventilation is designed and constructed based on a 7-rows cabin mockup and the pipeline system is the same as that in a retired MD-82 airplane.The study firstly measured the mean velocity and turbulence intensity of the jet flow field point by point via a high-frequency hot wire anemometer.Then the variations of the axial mean velocity and turbulence intensity are analyzed,so as the distributions of typical radial velocity.The simplified model of gasper jet is proposed considering the airflow rates and opening sizes,which can be used as the guidance of the theory analysis and CFD simulation.The distributions of the whole flow field of gasper jet are obtained by a 2D-PIV measurement system inside the 7-rows cabin mockup.Under real cabin environment,the gasper jet would be influenced by airflow rates,the mixing ventilation and the thermal plume created by passengers.So the real effect on passenger thermal comfort and cabin air quality of this traditional gasper is evaluated with the results above.Finally,we give some advice on optimization design of personalized ventilation in aircraft cabin environment.The study found that the flow field near the nozzle is complicated,but the central axial velocity reaches the maximum value when the distance equals to 1.8D0(D0 is the outer diameter of the jet outlet,D0=12.6mm),the jet becomes fully developed when the distance equals to 5D0 after the transition zone.The attenuation law of central axial velocity of gasper jet in fully developed zone is similar to that of a round jet,so the study proposed semi-empirical formula to predict the development of gasper jet,considering the airflow rates and opening sizes.The results of three different conditions inside the 7-rows cabin mockup indicates that not only the trajectory but also the velocity decay of the gasper jet is influenced by the mixing ventilation.The turbulent boundary of gasper jet is disturbed by mixing ventilation,which enhances the entrainment ability of jet and the central velocity decay.On the other hands,the thermal plume of passenger can cause the trajectory downward stretch.In order to avoid the draught sensation of passengers,the study suggests that the range of airflow rates is 0.48 l/s to 0.84 l/s.Moreover,the percentage of the fresh air for gasper jet is only 13.1%,which is not meet the requirement of personalized ventilation and needs further improved.