Simultaneous concentration and velocity maps in particle suspensions under shear from rheo-ultrasonic imaging

TL;DR

This paper advances ultrasonic imaging to simultaneously map concentration and velocity fields in sheared particle suspensions, enabling detailed analysis of heterogeneities caused by various flow phenomena.

Contribution

It introduces a method combining ultrafast ultrasonic imaging with rheological measurements to capture real-time concentration and velocity maps in non-Brownian suspensions under shear.

Findings

Successful calibration with homogeneous suspensions

Visualization of concentration heterogeneities due to centrifugation, instability, and sedimentation

Demonstration of technique's capability for detailed flow analysis

Abstract

We extend a previously developed ultrafast ultrasonic technique [Gallot et al., Rev. Sci. Instrum. 84, 045107 (2013)] to concentration field measurements in non-Brownian particle suspensions under shear. The technique provides access to time-resolved concentration maps within the gap of a Taylor-Couette cell simultaneously to local velocity measurements and standard rheological characterization. Benchmark experiments in homogeneous particle suspensions are used to calibrate the system. We then image heterogeneous concentration fields that result from centrifugation effects, from the classical Taylor-Couette instability and from sedimentation or shear-induced resuspension.