Experimental and numerical analysis of an apparatus to apply controlled shear/elongation in fluid flows

This paper reports on the detailed flow physics of a device to control shear/elongation in a fluid flow. The device consists of a sphere which periodically moves up and down inside an axisymmetric confinement. Detailed analysis of the flow field inside the setup is reported in this paper and an analysis of the flow structures and the shear rates inside the confinement is made. The flow field is experimentally measured using Time-Resolved Particle Image Velocimetry (TR-PIV) and numerically obtained by a Direct Numerical Simulation. The numerical simulations are validated with experimental data and the numerics were able to capture all the flow features found in the experiments. Shear rate profiles along pathlines are calculated and it was found that the shear rate profiles are very similar for different initial positions in the flow field. Due to the up and down movement of the probe, both positive and negative shear is created, which is not possible with other shear controlled devices such as rotating cylinders, moving plates, and contractions. Therefore, this apparatus is able to simulate more realistic flow conditions as can be found in the processing industry.