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Drag Reduction of Submerged Bodies Using Polymeric Coatings

In this paper, the applicability of polymeric coatings to reduce the drag experienced by submerged axisynunetric bodies was investigated experimentally. Two different commercial polymeric coatings were used for this study: 1) Polyacrylamide (PAA), and 2) Polydemethyl siloxane (PDS). Wheras the first polymer is water-soluble; in contrast, the second polymer is hydrophobic. Drag measurements were conducted on a model of the body of interest with a geometrical scale of 1/10. A home-made water column device was used to obtain drag data at Reynolds numbers up to 20,000 (large enough for the annular flow between the exterior of the model and the interior wall of the test cell to be taken as turbulent). Extensive test results obtained using this device revealed that both polymers are effective in reducing the drag coefficient in the range of 20-30 %. The effectiveness of PAA coating, however, was realized not to be steady apparently because of its being washed away by the flowing water. In contrast, steady drag reduction was found to be achievable using the PDS coating.