On Modeling the Response of Synovial Fluid: Unsteady Flow of a Shear-Thinning, Chemically-Reacting Fluid Mixture

TL;DR

This study models the unsteady flow of shear-thinning, chemically-reacting fluids in a simplified annular geometry to understand synovial fluid behavior, comparing three models and a Newtonian case.

Contribution

It introduces a semi-inverse method to analyze shear-thinning, reactive fluid flow in a simplified geometry, assessing different models for synovial fluid behavior.

Findings

Shear-thinning models show different flow responses compared to Newtonian fluids.

External pressure gradients significantly affect flow characteristics.

The semi-inverse method effectively simplifies the analysis of complex fluid models.

Abstract

We study the flow of a shear-thinning, chemically-reacting fluid that could be used to model the flow of the synovial fluid. The actual geometry where the flow of the synovial fluid takes place is very complicated, and therefore the governing equations are not amenable to simple mathematical analysis. In order to understand the response of the model, we choose to study the flow in a simple geometry. While the flow domain is not a geometry relevant to the flow of the synovial fluid in the human body it yet provides a flow which can be used to assess the efficacy of different models that have been proposed to describe synovial fluids. We study the flow in the annular region between two cylinders, one of which is undergoing unsteady oscillations about their common axis, in order to understand the quintessential behavioral characteristics of the synovial fluid. We use the three models suggested by Hron et al. [ J. Hron, J. M\'{a}lek, P. Pust\v{e}jovsk\'{a}, K. R. Rajagopal, On concentration dependent shear-thinning behavior in modeling of synovial fluid flow, Adv. in Tribol. (In Press).] to study the problem, by appealing to a semi-inverse method. The assumed structure for the velocity field automatically satisfies the constraint of incompressibility, and the balance of linear momentum is solved together with a convection-diffusion equation. The results are compared to those associated with the Newtonian model. We also study the case in which an external pressure gradient is applied along the axis of the cylindrical annulus.