Near-Wall Turbulence and Skin Friction Measurements Using Ionic Polymer Sensors

The purpose of this proposal is to demonstrate the feasibility of using novel ionic polymer sensors to measure flow-induced skin friction. Knowledge of the skin friction at the hull / water interface is critical to propeller and propulsion system design. Also, knowledge of the mean and fluctuating wall shear stress is important for understanding the details of flow separation and flow-induced noise. More importantly, a robust technique for measuring wall shear stress is needed to assess the effectiveness of new friction-reducing techniques, including the use of lubricants and micro-bubble injection. Current techniques to measure skin friction are hindered by several key limitations, including high cost, difficulty of implementation, and susceptibility to seawater corrosion. By contrast, ionic polymer sensors are low cost, thin flexible polymer membranes that can be affixed directly to the surface of a vessel with no modifications. Furthermore, they respond directly to flow-induced shear, thus making them ideal candidates for analyzing the effectiveness of friction-reducing treatments. Initial results with ionic polymer sensors reveal that the sensor output shows excellent correlation to theoretical predictions of skin friction. The Phase I effort will expand on this work by validating ionic polymer skin friction sensors using particle image velocimetry.