Blubber and compliant coatings for drag reduction in water II. Matched shear impedance for compliant layer drag reduction

The lack of a bioluminescence on a dolphin swimming at a speed of ~ 10 knots demonstrates that its boundary layer remains laminar up to this speed, and the corresponding Reynoldʹs number of Re 2 × 107. By contrast, for the equivalent rigid body, the transition from laminar to turbulent flow takes place in the region of Re 5 × 105. We identify this effect with special viscoelastic properties of the dolphinʹs thick (~ 3 cm) blubber. Preliminary measurements of the complex dynamic shear compliance of blubber shows that it is intermediate between softer compliant coatings that result in an increase in hydrodynamic drag, and harder compliant coatings that have no effect on drag. This appears to be explained by the Matched Shear Impedance Hypothesis.