Abstract
The increasing popularity of flow field-based data analysis (FFBDA) techniques has a paradigmatic example in the routines already developed for the rotational oscillating bicone bob interfacial shear rheometer. Such routines use a second order centered finite difference (SOCFD) discretization scheme, in both the vertical and radial coordinates, for the velocity field in the bulk fluid subphase and a first order forward finite difference (FOFFD) scheme in the vertical coordinate for the velocity field at the air/water interface. Such a mixture of schemes causes non-smooth flow fields at the interface that can be tackled by appropriately devising a SOCFD scheme for the vertical coordinate at the interface using a line of “phantom” nodes that merely serve to adequately merge the Navier–Stokes equations and the Boussinesq–Scriven boundary condition at the interface. Here we report on a detailed analysis of the quantitative improvements of such a scheme over the previous one by comparing the structure of the flow fields at and close to the interface, the differences in the interfacial and bulk drag torques on the bicone bob, and the differences in the torque/displacement complex amplitude ratio.
Highlights
Interfacial shear rheology aims at characterizing the shear mechanical properties of thin layers supported by a Newtonian liquid subphase
Variables obtained by means of program versions PV-I and PV-II will be labeled with subscripts I and I I, respectively
All of the results shown here have been obtained with a high resolution mesh (1000 × 500 nodes); the differences in the results obtained with program versions PV-I and PV-II have been minimized
Summary
Interfacial shear rheology aims at characterizing the shear mechanical properties of thin layers supported by a Newtonian liquid subphase. The availability of increasingly fast hardware (multi-kernel microprocessors and graphic cards) and powerful software platforms (MATLAB® , GNU Octave, Python® , Mathematica® , etc.) has dramatically decreased the computational time to the level that, nowadays, including such flow field-based data analysis (FFBDA) routines for real-time processing of the experimental data in modern interfacial shear rheometers is conceivable [6]. The first FFBDA scheme Reynaert et al [7] was designed for the magnetic needle ISR in the Helmholtz coil configuration, that was soon followed by another scheme designed for the double wall-ring (DWR) rotational interfacial shear rheometer [8]. Let us mention here that data analysis is not the only source of inaccuracy in interfacial rheometry; for a thorough discussion of experimental problems that affect measurement accuracy see, for instance, reference [12]
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