Experimental Study On Flow Field Under Mixing/Displacement Ventilation

With the improvement of living standards,most people nowadays tend to choose convenient and fast aircraft as a travel tool.The aircraft is in a closed environment.The air quality in the cabin is closely related to the thermal environment and the air conditioning and exhaust system.Improper ventilation will increase the passenger’s discomfort.If a passenger carries a pathogen,it may even spread the disease.In this paper,the characteristics of the flow field under the two types of mixing ventilation methods commonly used in passenger aircraft and displacement ventilation in the research and development stage were studied.This experimental study was carried out in a full-size seven-row cabin model in which 42 fixed-temperature manikins were placed to s imulate passengers,and the transition between mixing and displacement ventilation was achieved by adjusting the duct valves.The cabin was insulated to ensure that the flow field in the cabin is not disturbed by the external environment.The flow field of the cabin had high pulsation and unsteady characteristics.The air supply boundary,wall temperature and human thermal plume would aggravate the instability of the flow field.Even if the geometry was symmetrical,the flow field was not symmetrically distributed.Aiming at the problem of asymmetric distribution of passenger flow field,the symmetry of the air supply boundary was ensured by the method of uniform air supply,and the influence of flow field distribution characteristics and human thermal plume on the flow field was explored.The velocity field,turbulence intensity field,and turbulent kinetic energy field under different ventilation modes were analyzed.In the case of uniform air supply,the flow field is very sensitive to the human thermal plume,and the human thermal plume could make the velocity field in the cabin more uniform and also make the flow field more unstable.In the mixing ventilation mode,the flow field would form a large-scale vortex structure.As the human thermal plume intensity was different,the vortex structure changed significantly.The trend of turbulence intensity caused by human thermal plume was opposite to that of velocity,while the trend of turbulent kinetic energy showed a significant positive correlation between jet region and velocity changed region.The uniformity of the whole field speed of the two ventilation modes was very similar,but the eddy current formed under the full ventilation of the mixing ventilation will expand the spread range of the pollutants,and the replacement ventilation had no obvious eddy current,which was more conducive to timely discharge of pollutants and the heat.Displacement ventilation had better performance in eliminating pollutants and saving energy.