Affiliations: Temasek Laboratories, National University of Singapore, Engineering Drive 2 Singapore 119260,
SINGAPORE.
E-mail: [email protected]
Note: [] Corresponding Author
Abstract: The effect of a turbulent boundary layer subjected to a series of
rounded edged shallow dimple arrays with dimple depth ratios, d/D of 4%, 8% and
12% were experimentally studied. Measurements show the existence of a higher
flow speed region at the center of each dimple. The spanwise distribution of
the mean wall shear stress immediately downstream of the centers of the last
row of dimples does not vary with dimple depth, and is about 45% over that
without the dimple array. Turbulence measurements and surface flow
visualization shows that the flow over the shallowest dimple differs from the
deeper dimples. Flow separation observed with the deeper rounded edged dimples
produce similar flow structures as those from sharp edged dimples reported in
the literature. However flow separation is not observed when d/D = 4% but
instead two other higher speed regions either side accompany the central flow.
The effects of the dimples are rapidly suppressed by the flat surfaces between
of the dimples, and the flow rapidly reverts back to an unmanipulated flat
boundary layer flow in these areas.