In commercial airliner,the mixing air distribution system in which air enters the cabin from the multi-slot diffusers underneath the luggage compartments and exhausted near the floor are most commonly used for air circulation,which result in two-jet collision regions with strong uncertainty and unsteady characteristics in cabin.In such unsteady regions,previous time-averaged data may miss much valuable information for studying thermal comfort,researching contaminant transport and verifying unsteady simulation modes.In this study,to experimentally explore more unsteady characteristics in cabin,we focused on this two-jet collision region in the middle of the aisle in the cabin,and a long time series of velocity fields was measured by particle image velocimetry (PIV) with a sampling frequency of 3 Hz under both isothermal and cooling conditions.Through the measured data,the fluctuation characteristics of four typical points were discussed and compared under two operating conditions.By observing the long time series of the measured transient flow field,three typical instantaneous airflow fields were identified under each of the two conditions.Then,POD analysis was utilized to mathematically reveal the coherent structure from the various instantaneous flow fields.These high-quality experimental data of instantaneous flow fields are also valuable for validating transient simulation models.