Attenuation of near-wall turbulence in turbulent boundary layers over a perforated surface

Abstract: The potential application of a perforated structure for reducing near-wall turbulence in turbulent boundary layers is investigated in this work. The structure consists of a backing chamber underneath a perforated plate. Near-wall turbulence structures were analyzed using hot-wire measurements. At Reynolds numbers Re = 1165 and 2294, different inner-scaled chamber volumes, ranging from V+ = 2.4x10^6 to 11.5x10^6, were investigated to modify turbulent boundary layers. The findings show that the perforated structure significantly impacts near-wall turbulence formations. Within the near-wall region (y+ <= 30), statistical analysis using the variable-interval time-averaging (VITA) technique revealed a decrease of up to 9% in sweep intensity and a decrease of roughly 33.5% in sweep frequency, suggesting that the perforated structure weakened burst events in this area. The perforated structure's ability to move turbulence energy away from the wall resulted in lower shear stresses and skin friction drag, leading to a reduction in turbulence intensities near the wall by up to 9%. It was also demonstrated that as the inner-scaled chamber volume increases, the near-wall turbulence decreases more significantly. Keywords: Turbulent boundary layers, Turbulent boundary layer control, Perforated surface