Experimental Study Of Impinging Jet And Turbulent Thermal Convection Base On The Aircraft Cabin Environment

Aircraft cabin is a closed,narrow and densely populated special microenvironment,the major factors influencing the airflow distributions in the cabin include the flows discharged from air outlets by the air supply system,the respiratory airflows produced through mouths and noses of the passengers and the thermally driven air currents caused by the heat dissipation of the passengers and aircraft,as well as the separated flows caused by the complicated geometric structures in the cabin.The flows discharged from the air supply outlets as well as the mouths and noses of the passengers are analogous to the free jets,which produce impinging effect when they encounter the seats and other facilities,and the thermally driven air flow movements caused by the heat dissipation of the passengers form the turbulence thermal convections.Therefore,the airflows in the local space of the aircraft cabin are complex flows including the impinging jets and the turbulence thermal convections.The investigation of the airflows in the aircraft cabin local space is essential prerequisite to create a safe,comfortable and healthy aircraft cabin environment.In this paper,the impinging jet and turbulence thermal convection based on the aircraft cabin environment studied experimentally by the use of hot-wire anemometry and particle image velocimetry are taken as the basic of the airflow investigation in the real aircraft cabin.The flow characteristics of turbulent impinging jet have been experimentally studied by use of hot-wire anemometry.The radial distributions of the normal and radial velocity components in the free-jet region and the the normal distributions of the radial and normal velocity components in the wall-jet region,have been measured finely with the resolution higher than the smallest time-scale of turbulence by the use of the standard X wire probe and the boundary layer X wire probe together with IFA300 anemometer.Mean velocity,turbulence intensity,higher-order moments,power spectrum and dissipation spectrum as well as spatial characteristic scale distribution results are obtained.Wavelet transform and Hilbert-Huang transform have been applied respectively to analyze the multi-scale(multi-mode)characteristics of the impinging jet and the turbulent energy cascade processes through the energy spectrum of different scales(modes)are described,as well as these two decomposition methods are compared.It is found that Hilbert-Huang transform can more accurately depicting the change and function of different scales(modes)during the turbulent energy transfer process.Eventually,the mean frequencies of different mode structures and the energy densities of flow structures with different mean frequencies in the free-jet region and wall-jet region have been obtained by Hilbert-Huang transform method.The respiration flow fields of a thermal manikin under the isothermal and heated conditions have been studied experimentally by use of particle image velocimetry.Periodical phase average method has been applied to perform the turbulence statistics of periodical turbulent fields measured under these two conditions,and the evolution characteristics of temporal and spatial distribution of phase mean velocity,turbulence intensity and vorticity have been obtained.The instantaneous flow field of respiration has been decomposition into four parts,namely mean filed,coherent field,transition field and turbulent field,flow characteristics,evolution law as well as cyclic variation characteristics of these four flow fields studied by employing POD method.Spatial corss-correlation technique has been adopted to study variation the phase relation between Reynolds stresses and velocity strain rates for different phases under these two conditions.