Influence of the thickness of monolithic compliant coatings on the skin friction drag

In this study, the drag reduction capabilities of compliant coatings made from viscoelastic silicon rubbers are verified experimentally. A series of single-layer compliant coatings of homogeneous materials with constant thicknesses were used. The experiments were performed at different flow velocities in a high-speed water tunnel of Pusan National University. They were accompanied by experimental determination of dynamic viscoelastic properties of the coating materials. Then, for each coating, a dynamic compliance in frequency domain was estimated. Assuming that the coatings interact effectively only with dynamic structures of turbulent boundary layer in a frequency band corresponding to the region about the maximum compliance, promising ranges of flow velocity and coating thickness are outlined. The predicted ranges are compared favourably with the experimental observations in the high-speed water tunnel