Skin friction drag reduction over staggered three dimensional cavities

摘要

The effect of three-dimensional staggered circular cavities on a zero-pressure gradient incompressible turbulent boundary layer was studied. Two key parameters were varied, being the ratio of the diameter, d, to the depth, h, of the cavity, d/h and the Reynolds number based on the diameter of the cavity, R-d. Velocity profile measurements showed that for the cases of d/h 1 an increase in skin friction drag was experienced with respect to a smooth surface, but for d/h = 1 the drag increment was almost negligible and in some cases it was lower than that of a smooth surface by up to 10%. Measurements along the spanwise plane showed the presence of organised transverse velocity components which bear some resemblance with the flow over riblets. The skin friction drag appears to be a strong function of R-d, where for R-d 5500 a drag increment is experienced which could potentially be due to shear layer breakdown and more production of turbulence. (C) 2018 Elsevier Masson SAS. All rights reserved.