Experimental Study on the Drag Reduction by Injection of Microbubble and Polymer Solution in a Water Tunnel for Water-Borne Vehicles

Experiments on the friction drag reduction by injecting microbubbles or polymer solutions have been carried out for both a flat wall and an axisymmetric body. In the first setup, the drag reduction on the flat ceiling of a water channel was measured for a fully developed turbulent channel flow by using a newly developed skin friction sensor of floating element type. The effects of key controlling parameters were investigated for higher drag reduction with varying the concentration and the injection rate of the additives. The integrated frictional drag has been reduced up to 25% with the microbubble injection and 50% with the polymer solution injection. The drag reduction for a slender axisymmetric body was also investigated in a cavitation tunnel based on the parameters obtained from the channel experiments.