Turbulence characterization of instantaneous airflow in an aisle of an aircraft cabin mockup

Abstract

The turbulence characteristics of instantaneous airflows in an aircraft cabin mockup are measured by high-frequency mini particle image velocimetry (mini-PIV) and analyzed by higher-order turbulent statistics. Under maxing ventilation in the aircraft cabin, two jets from the diffusers collide each other in the middle of the aisle. The airflows of collision regions in an aircraft cabin are typically turbulent, with a low velocity magnitude and a high fluctuation. Although the average airflow fields are uniform and have a smaller velocity gradient, the instantaneous airflow fields are remarkably unstable. Turbulence scales are utilized to analyze the spatial and temporal characteristics of the instantaneous airflows. The maximum airflow vortex scale of the collision zone is 11 cm, and the minimum vortex scale is only 8 × 10−4 m. The inertial sub region of the airflow power spectrum in the collision region is approximately 4–10 Hz. The wavelet coefficients of instantaneous fluctuation velocity have a quasi-periodicity of approximately 0.5 s, when the scale factor is 54. The grid size of direct numerical simulation (DNS) is recommended to be less than 0.3 mm, that of the large eddy simulation (LES) should be between 0.3 and 100 mm and that of the Reynolds-average Navier-Stokes (RANS) should be larger than 100 mm and smaller than the characteristic scale of airflows. The LES unsteady simulation time step should be less than 0.1 s, and the time step of RANS method should be less than 0.25 s. The power spectrum exponent of the instantaneous airflows in the aircraft cabin mockup is between 1.2 and 1.8, similar to natural wind, and will thus have a beneficial impact on human comfort.