Drag Reduction Technologies

Abstract : Diluted polymer solutions, surfactants, microbubbles and compliant coating as drag reducers have been reviewed in this report. The advantages and disadvantages of each method have been discussed. For the polymer solutions, it is possible to achieve up to 80% drag reduction with only a few parts per million of polymer. Ionic and non-ionic surfactants can also offer similar drag reduction as polymer solutions but at a high concentration of few percent. Microbubbles are perhaps the cheapest and non-polluted drag reducer. However, the control of the bubble size and the angle of ejection can impose technical challenges. This method can be combined with other drag reduction (DR) technologies such as polymers to enhance its effectiveness. Compliant coatings can be designed to behave in a similar fashion to the skin of a dolphin. The development of the compliant coating is theoretically complicated, although the optimized coating can offer a DR up to 50%. Despite the extensive research in the area of DR over the past four decades, for each DR technology there is no universally accepted model that explains the DR mechanism. Application of DR technology with microbubbles to the ship hull indicated a 10 - 15% reduction in drag. The full scale testing of a submarine by the U.S. Navy has shown that polymer ejection has the potential to reduce the self-noise, drag and radiated noise generated by the propeller.