Eddies and interface deformations induced by optical streaming

TL;DR

This paper investigates how laser-induced optical streaming causes flow patterns and interface deformations in two-layer fluids, combining analytical and numerical methods to predict effects of geometry, scattering, and viscosity.

Contribution

It provides a combined analytical and numerical analysis of optical streaming-induced flows and interface deformations in two-layer fluids, including predictive simulations and theoretical insights.

Findings

Flow patterns depend on geometry, scattering strength, and viscosities.

Analytical and numerical results show good agreement.

Secondary flows are robust and emerge under various conditions.

Abstract

We study flows and interface deformations produced by the scattering of a laser beam propagating through non-absorbing turbid fluids. Light scattering produces a force density resulting from the transfer of linear momentum from the laser to the scatterers. The flow induced in the direction of the beam propagation, called 'optical streaming', is also able to deform the interface separating the two liquid phases and to produce wide humps. The viscous flow taking place in these two liquid layers is solved analytically, in one of the two liquid layers with a stream function formulation, as well as numerically in both fluids using a boundary integral element method. Quantitative comparisons are shown between the numerical and analytical flow patterns. Moreover, we present predictive simulations regarding the effects of the geometry, of the scattering strength and of the viscosities, on both the flow pattern and the deformation of the interface. Finally, theoretical arguments are put forth to explain the robustness of the emergence of secondary flows in a two-layer fluid system.