Salivary mucins for turbulent drag reduction

Abstract

The operational efficiency of fire suppression systems, municipal sewage networks, marine vehicles, and various other technologies are constrained by the large viscous frictional drag associated with fluid turbulence. This provides a strong incentive to develop engineering strategies that attenuate turbulence, ultimately mitigating the carbon footprint of large-scale hydrodynamic applications. We demonstrate the effective use of natural salivary mucins as a cost-effective, widely accessible drag-reducing additive. Diluted samples of human saliva are shown to substantially reduce frictional drag (up to 30%), with similar efficacy as synthetic drag-reducing polymers. Saliva contains long glycoproteins that can physically associate to form a supramolecular network with a large extensional viscosity. The non-Newtonian rheology of dilute solutions of glycoproteins makes them well-suited for turbulent drag reduction (DR). Under sustained turbulent flow conditions, the supramolecular associations of the mucin network slow the effects of mechanical degradation, resulting in more persistent DR compared to synthetic hydrocarbon polymers.