Modification of near-wall turbulence in turbulent boundary layers due to a perforated structure

Abstract

This study investigates the potential of a perforated structure for the control of near-wall turbulence in turbulent boundary layers. The perforated structure consists of a perforated plate, underneath of which is a backing chamber. The near-wall turbulent structures were analyzed using hot-wire measurements. Different inner-scaled chamber volumes from V+=2.4×106 to 11.5×106 were considered to manipulate turbulent boundary layers at two Reynolds numbers of Reθ = 1165 and 2294. The findings reveal significant effects of the perforated structure on near-wall turbulent structures. Statistical analysis utilizing a variable-interval time-averaging technique illustrated a reduction of up to about 9% in sweep and ejection intensity, a decrease in about 25% in ejection frequency, and a decrease in approximately 33.5% in sweep frequency within the near-wall region, y+≤30, indicating that the perforated structure weakened burst events in this region. In addition, the perforated structure lifted the turbulence energy further from the wall. Consequently, there was a reduction of up to approximately 9% in turbulence intensities near the wall, contributing to locally diminished shear stresses and skin friction drag. When the inner-scaled chamber volume increased, the reduction in near-wall turbulence became more pronounced.