EXPERIMENTAL METHOD FOR DRAG REDUCTION BY COMPLIANT COATING

The drag coefficients on discs rotating in a cylindrical tank has studied in relation to the nature of a composite coating attached to the underside of the disc, and direct comparisons were made with refrence discs of identical geometry which were completely rigid. The composite coating was formed by : (1) binding of velvet fabric to the metal disc with velour face outward, (2) casting a premixed silicone compositions over the velvet fabric, (3) covering the silicone layer with a this, stiff polymer film. As a result of the rests in certain cases drag coefficient was reduced by 20% of more as compared to refrence rigid discs. Two conclusions are possible : (1) true reduction of energy exchange in the turbulent boundary layer was achived, perhaps by damping of the turbulent bursting process ; (2) A significant increase in the laminar region at the center of disc was obtainded (transition of the coating . the change of drag coefficient of discs to be strongly influenced by the dynamic mechanical properties of the silicone elastomer network.

Keywords:

Compliant Coating , Drag Reduction , Transition Delay , Turbulence