Characterisation of bursts in a turbulent boundary layer over circular cavities

Abstract

Boundary layer surveys are performed to characterise the turbulent boundary layer grazing over a a surface with flush-mounted circular cavities disposed in a staggered arrangement (staggered angle of 45 deg). The momentum thickness based Reynolds number varies from Reθ = 1830 to 3380 and the cavity diameter and spacing in wall units from d+ = 130 to 250 and L+ = 587 to 1075 respectively. A decrease in the local skin friction drag with respect to a smooth baseline is evidenced as well as a thickening of the viscous sublayer. The bursts frequency profile for the perforated case is shifted away from the wall while the intensity of the bursts is reduced. The production term of the turbulent kinetic energy budget is obtained from Particle Image Velocimetry data. An upward shift and a decrease in magnitude of the peak associated with the streaks suggests that the cavities modify the near wall turbulent cycle