Experiments on the effects of aging on compliant coating drag reduction

Abstract

We report the experimental results from a collaborative effort between USA, Russia, and UK on the development of compliant coatings for undersea application of reduction of drag. The focus is on “shelf-life” of coatings. The coatings are based on a linear interference theory of interaction between turbulence pressure fluctuation and the viscoelastic 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 silicone coatings have been manufactured whose properties include slow and fast damping, slow and fast aging, and varying magnitudes of elasticity, density, and thickness as well as transparency. The dynamic modulus and loss tangent vary weakly over a range of frequencies and temperature allowing compatibility with broad spectrum of turbulence. Drag measurements have been carried out over a year by the three teams in their water tunnels independently of identical coated models. We show that, with some exceptions, drag reduction generally deteriorates with the age of the coatings.

Aluminum nitride–filled elastic silicone rubber composites for drag reduction

“…31 First, selected an approximate linear scatter near the yield point from the tensile strength test. Second, calculated stress (d) and strain (e) according to equations (2) and (3) using these scatter points. Third, plotted strainstress scatter diagrams and performed linear fitting.…”

“…Most of the researches have focused on the mechanism of skin elasticity [1][2][3][4] and special skin structure 5,6 to control the fluid medium. Some research also indicates that boundary heating mechanism by the dolphin's skin reduces the viscosity of the fluid, which leads to drag reduction, because there is a 9°C difference in temperature between the dolphin's skin and the boundary layer fluid when a dolphin is swimming at high speed.…”

Frictional drag reduction in microchannel using slip on convex air bubbles naturally formed in a specifed a cavity

“…The slip of a liquid on a solid wall occurs in many engineering situations such as lubrication [1], the flow on porous media [2], coating [3] and particle aggregation [4] and so on. Recently, its use to reduce the frictional drag has drawn attention in the miniaturized devices in which the critical dimension reaches to micro and nano scale [5].…”

Measurement of Dynamic Properties of Viscoelastic Materials

“…The dynamic properties of these materials such as modulus of elasticity and loss tangent as functions of frequency are of primary importance in designing such devices. In addition, it has been recently reported that information on the dynamic properties is crucial in optimizing design parameters of the compliant coating for the reduction of turbulent flow skin friction [3].…”