Hydrodynamic cavitation in Stokes flow of anisotropic fluids

Tillmann Stieger,Martin Schoen,Anupam Sengupta,Hakam Agha,Marco G Mazza

doi:10.1038/ncomms15550

Abstract

Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domain nucleates due to sudden pressure drop upon flow past a cylindrical obstacle within a microchannel. For an anisotropic fluid, the inception and growth of the cavitation domain ensued in the Stokes regime, while no cavitation was observed in isotropic liquids flowing under similar hydrodynamic parameters. Using simulations we identify a critical value of the Reynolds number for cavitation inception that scales inversely with the order parameter of the fluid. Strikingly, the critical Reynolds number for anisotropic fluids can be 50% lower than that of isotropic fluids.

Highlights

Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications
We find that the critical Reynolds number, Recr, scales inversely with the order parameter of the anisotropic liquid
With an average flow speed of 800 mm s À 1 (Er 1⁄4 200), the velocity reaches a maximum of 4,000 mm s À 1 at the constriction. This corresponds to Er 1⁄4 945 and Re 1⁄4 0.1, a hydrodynamic Stokes regime

Summary

Introduction

Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. The life time of a cavitating bubble can depend on a number of factors: volume of dissolved gases in the liquid matrix, presence of inclusions (for example, particulate matters) or pre-existing nucleation sites (for example, gas bubbles) and roughness of the solid surfaces in contact with the liquid Such multiparameter dependence can pose technical challenges to study cavitation experimentally—a possible explanation for the lack of corresponding investigations in anisotropic liquids. Anisotropic liquids constitute a special class of complex, non-Newtonian liquids, in which the molecules exhibit long-range order in their orientations or positions Common examples of such liquids include liquid crystals (LCs)[30,31], polymeric liquids far from equilibrium (LC polymers)[32] and electro/magnetorheological fluids. Any attempt to study hydrodynamic cavitation in LCs is still largely lacking

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Conclusion