Learning Forum

[petrsokr]

Hello, I am trying to simulate in CFX the flow of a non-newtonian fluid (blood) in a cylindrical tube. I am using the Bird-Carreau model for shear-thinning fluids like blood and I have found the parameters from bibliography. In results, I am trying to plot the viscosity profile at the end of the tube but the results seem to be the opposite of what I expected. The dynamic viscosity appears to be the lowest in the center of the tube and the highest at the wall. I don't think there is anything wrong with the model, maybe the numerical solution encounters a problem at r=0. Do you have any ideas on how to get the correct results? Thanks.

 

[NickFL]

What do your hand calcuations say the viscosity on the centerline should be? At the centerline what is the shear rate? Plug this into your viscosity equation to find \mu and compare.

As for the solver having a problem at r=0, look closer at the equations it is solving. Where does r appear?

[Rob]

To add to Nick's comments - what does the velocity contour look like and how well resolved is the mesh? Also check the actual values reported - is blood really that viscous?