Aircraft cabin is a closed,narrow and densely populated special environment.Due to crowded space,limited ventilation,and prolonged exposure time,the current ventilation is subject to causing the passengers complain about their comfort.As a supplement to the mixing ventilation system,the personalized ventilation system is utilized for rapid ventilation and heat exchange,which has attracted extensive investigation in building industry and aircraft cabin environment.This paper is based on the National Basic Research Program of China(973 Program)“Research on the key scientific issues in the control of air environment in large aircraft cabin”.The jet airflow field of personal airflow outlet(PAO)in MD-82 aircraft cabin is measured by hot wire anemometry(HWA)and time resolved particle image velocimetry(TR PIV)respectively.Many turbulence analysis methods are employed to study the jet airflow field.From the HWA results,a range with relative constant velocity and low turbulence intensity is formed beyond the reattachment point in the airflow field of the PAO jet.This range,i.e.the“second potential core”,is equivalent to a single jet potential core,and the airflow field beyond the reattachment point is similar to the single jet.However,the PAO jet develops faster and diffuses stronger than the single jet.From the point of the view of the numerical simulation,the calculation process can be greatly simplified if the velocity inlet boundary is set at the beginning of the“second potential core”,which can ignore the existence of the counter-gradient transport region.In the jet near-field region,the peak frequencies are found by spectrum analysis,and represent the formation of primary large-scale structures.Compared with the single jet,the peak values of the spectra in the PAO jet appear earlier,and the corresponding frequencies drop faster with air flow developing downstream.In the far-field region of both single jet and PAO jet,the power-law exponents of the inertial range in the jet centerline are found be approximately-3/2,not‘5/3’according to the famous exponent of K41.Moreover,by wavelet analysis,it shows that the energy proportion distributions over scales are varied at different axial positions,and the scale containing the maximum energy increases along the axial direction.To acquire more information of the airflow field and the spatial turbulent structures of the PAO jet,we measured the airflow field by time resolved particle image velocimetry.A good agreement is found between the measured results of TR PIV and HWA.The spatial distributions of eddy viscosity coefficients calculated by different component of the Reynolds stress tensor and the velocity gradient tensor are various,which indicates that the airflow field is anisotropic and non-equilibrium.The value of the production of turbulent kinetic energy in the shear layer is positive beyond the reattachment point,which is similar to the single jet.However,before the“second potential core”,the negative value,i.e.negative energy production region,appears.Therefore the turbulent fluctuation is suppressed,and then the“second potential core”is formed.Theλci criterion is employed to visualize the vortices,not limited to describe the vortex structures by only using the vorticity distribution of the airflow field.Moreover,the proper orthogonal decomposition(POD)method is employed to extract the large-scale turbulent structures.We find once the cumulative energy of POD modes occupies over 60%of the total turbulent kinetic energy,the reconstructed fluctuating velocity field can represent the large scale coherent structures.Meanwhile the small scale POD reconstructed field is close to the homogeneous isotropic turbulence.Finally,to improve the original jet airflow field,the wedges structures are added on the personal airflow outlet.We measured the modified airflow field and found that velocity decays faster and turbulence intensity is lower in the far-field region.These changes imply that the measure improves the passengers comfort in the aircraft cabin. |