## Appl Rheol online available publications for selected issue

Follow the blue link(s) below for abstracts and full text pdfs .

► Cite this publication as follows:

Baller J, Wagner C, Roose P: Joint Symposium Rheology - 360° of the Belgian Group of Rheology, German Rheological Society, and ProcessNet-Subject Division Rheology, Appl. Rheol. 28 (2018) 53.

Two geometrical models are developed to simulate fluid transport via peristaltic motion in tubes of uniform or linearly decreasing radius: A 2-D axisymmetric tubular model and a 2-D axisymmetric conical model. In both models, peristaltic motion is induced by a traveling wave along the wall of the computational domain which deforms the wall and the computational mesh. These geometrical models are coupled with a finite volume solver from the open source software package OpenFOAM which is used to simulate the peristaltic flow for different Newtonian and non-Newtonian fluids in the laboratory (or Eulerian) frame of reference. After validation of the solver with experimental data, simulations are performed in each geometrical model to determine the influence of a given set of parameters on peristaltic flow behavior and transport efficiency. The parameters that are varied include the wave speed, relative occlusion, Newtonian viscosity, and power-law index for shear-thinning non- Newtonian fluids. For both computational models, the transport efficiency is found to increase strongly with relative occlusion, to decrease as the amount of shear-thinning increases, and to be independent of wave speed. In the tubular model, transport efficiency is found to be independent of Newtonian viscosity, while in the conical model, it decreases as viscosity decreases for Reynolds numbers greater than one.► Cite this publication as follows:

Alokaily S, Feigl K, Tanner FX, Windhab EJ: Numerical Simulations of the Transport of Newtonian and Non-Newtonian Fluids via Peristaltic Motion, Appl. Rheol. 28 (2018) 32832.

The oscillatory shear rheological behaviors of a polyolefin plastomer (POP) at various temperatures were examined within its linear viscoelastic (LVE) regime. The apparent storage modulus, loss modulus, complex modulus, complex viscosity, and phase angle of POP at various temperatures are all found gap dependent, revealing that wall slip occurred under the applied oscillatory shear with the shear stress amplitude controlled constant. All Han plots and van Gurp-Palmen (vGP) plots of POP samples overlapped each other at various gaps at a certain temperature, suggesting that a time-gap-superposition (TGS) is valid with all the apparent angular frequency dependent storage modulus and loss modulus of POP at various gaps shifted to their master curves at a selected reference gap. This indicates that the wall slip can be understood as adding a dashpot in series to POP sample only with the apparent relaxation time multiplied by a shift factor. By TGS, a method to determine the wall slip length b and the actual oscillatory shear rheology of the fluids was consequently established. The results showed that the obtained b is dependent on temperature and wall slip made it possible to extend the experimental angular frequency range to lower frequencies. Further analysis revealed that wall slip did not influence the Arrhenius viscosity dependence of POP on temperature, while the viscous flow activation energy decreased.► Cite this publication as follows:

Li J, Wang L, Yu D, Christiansen JdC, Jiang S: Wall Slip of Polyolefin Plastomers under Oscillatory Shear, Appl. Rheol. 28 (2018) 33226.

Spiral blood flow in the aorta is helpful in maintaining the stability of flow, reduction in lateral forces, turbulence near walls, and shear stress index. Thus, it helps in the prevention of diseases, such as atherosclerosis and atherogenesis, in the aortic arch because of the reduced accumulation of low-density lipoproteins (LDLs). To investigate the actual physics behind the aforementioned phenomenon, we conducted a fluid-structure interaction (FSI)-based numerical simulation of the threedimensional aortic arch model under the influence of a pulsatile spiral flow. Spiral flow was introduced through the use of a mapping methodology between a spiral graft model and aortic model. The physics of time dependent pulsatile spiral turbulent flow was coupled with the structural mechanics of the aorta by using the FSI method. Results showed that the exterior interface of the aortic arch tends to rupture under the actions of centrifugal forces and secondary flow counter-rotating vortices in addition to applied pressure forces. Under systolic and diastolic conditions, the interior and exterior interfaces of the aortic arch both had small displacement, thus showing the insignificant role of velocity gradients in wall deformation. Moreover, LDL accumulation in the aorta under the influence of pulsatile spiral flow has been investigated using particle tracing methodology. The LDLs were evenly distributed in the aorta because of the influence of spiral flow. This result shows that spiral flow can contribute to the elimination of threats from diseases, such as atherosclerosis and atherogenesis.► Cite this publication as follows:

Ashraf F, Cheema TA, Park CW: The Impact of Pulsatile Spiral Flow on the Wall Deformation Characteristics and Low-Density Lipoproteins Accumulation in the Aorta, Appl. Rheol. 28 (2018) 35702.

Rheological properties of KCl/polymer type drilling fluids containing particulate loss prevention material (LPM) were characterized by an integrated inverse model-experimental approach. Rheological measurements for LPM-laden KCl/polymer type drilling fluids were carried out on a 6-speed rotational viscometer. The algorithm based on Tikhonov regularization was validated to be applicable and reliable to compute the shear rate in a rotational viscometer equipped with a widened annular gap. With the validated algorithm, the dial readings versus rotational speed data were transformed into shear stress vs. shear rate form. The results indicate that the rheological diagrams of the KCl/polymer type drilling fluids resemble those of a yield stress fluid and can be well represented by the Hershel-Bulkley model. The observed variation shows that rheological parameters were affected significantly by the addition of particulate LPM. The amount and the particle size of particulate LPM have a combined effect on the rheological properties of LPM-laden KCl/polymer type drilling fluids.► Cite this publication as follows:

Wang G, Du H: Rheological Properties of Kcl/Polymer Type Drilling Fluids Containing Particulate Loss Prevention Material, Appl. Rheol. 28 (2018) 35727.

© Applied Rheology 2024