NUWC-Russia-UK Collaborative Research on Compliant Coatings

We report the results from a collaborative effort between NUWC, Russia and UK on the development of compliant coatings for undersea application of reduction of drag and wall-pressure fluctuations. The coatings are based on a linear interference theory of interaction between turbulence pressure fluctuations and the visco-elastic coating. The phase shift between boundary displacement and pressure fluctuation embodies the interference effect. The natural frequency of the coating is matched to the turbulent boundary layer region of maximum Reynolds stress production. Low molecular weight rubber-like coatings have been manufactured whose properties include slow and fast damping, slow and fast ageing, and varying magnitudes of elasticity, density and thickness. The dynamic modulus and loss tangent remain constant over a range of frequencies and temperature allowing compatibility with broad spectrum of turbulence. Drag measurements have been carried out between 0-5 m/s by the three teams in their water tunnels independently on five identical coated axisymmetric models. Reduction of drag has been observed by all three teams.