Orthogonal wavelet decomposition of turbulent structures behind a vehicle external mirror

The turbulent structures of various scales around an externally mounted vehicle mirror have been experimentally investigated. The high-speed PIV technique was first used to measure the instantaneous velocity fields of the mirror wake at a Reynolds number of 7900 in the (x, y)-, (x, z)- and (y, z)-plane. The distribution of instantaneous streamlines and vorticity, time-averaged streamlines and Reynolds stresses were examined. Then the instantaneous turbulent structures were decomposed into the large-, intermediate- and relatively small-scale structures by the wavelet multi-resolution technique. It is found that the large-scale vortical structure shed from the root and side portion of mirror forms the separation region, the intermediate- and relatively small-scale structures are respectively generated from the tip of the mirror and the edge of the mirror. The relatively small-scale structures exhibit the strongest vorticity concentration. It is also indicated that the large-scale turbulent structure makes the largest contribution to the Reynolds stress in the range of separation shear layer behind the separation region. The relatively small-scale structure, however, makes a more contribution to the Reynolds stress in the shear layer near the mirror.