Discussion Forum

Dear people,

I've recently started using COMSOL (v5.2a), and I was wondering if somebody could help me. At the moment I'm trying the simulate a flow of a Non-Newtonian fluid, a magnetorheological fluid. This means that the dynamic viscosity of it isn't constant, and therefore I want to implement the Bingham-Papanastasiou model for this dynamic viscosity.

An already predifined model in COMSOL for Non-Newtonian fluids is the Carreau model, and here the dynamic viscosity is defined as a function with definitions for the shear rate and strain rate tensor. My main purpose is actually to alter the expression for the dynamics viscosity, because the definitions for the shear rate and the strain rate tensor I will use also.

Nevertheless I don't know how to do this. I was looking at the section where you can define your own parameters and functions, but I don't know how to implement the tensors and vectors for example.

The Bingham-Papanastasiou model is defined as the following: http://www.scielo.br/pdf/jbsmse/v32nspe/a04v32nspe.pdf

n = n0 +[ tauy/shearrate] * [1 - exp(-m*shearrate)]

Here n is the dynamic viscosity, n0 is the plastic viscosity, tauy is the yield stress and m is the regularizing parameter. The shear rate and strain tensor D are defined as following, just as in COMSOL for the Carreau model.

shearrate = [2trace(D)^2]^0.5, D = 0.5[div(u) + div(u)^T]

This model I want to implement in COMSOL, any tips on how to do this? Thanks in advance!

Regards,

Marc