Thank you for your answer. For the single phase model, I used one value in my UDF for the strain rate, which is epsilon_RBC = 0.45 (meaning it's just a fixed parameter).
Yes the plasma viscosity is Newtonian, which is why I model the RBC viscosity to be non-Newtonian. Then the total viscosity is calculated using: mu_mix = mu_rbc*VOF_rbc + mu_plasma*VOF_plasma.
The C-Y properties are deducted from the following paper:
Jonghwun Jung, Robert W. Lyczkowski, Chandrakant B. Panchal, and Ahmed Hassanein. Mul-
tiphase hemodynamic simulation of pulsatile flow in a coronary artery.
Journal of Biomechanics, 39(11):2064 – 2073, 2006. ISSN 0021-9290. doi: https://doi.org/10.1016/j.jbiomech.2005.06.023