CFD – Modeling Viscoplastic Fluids
Posted on July 14, 2022 Computational Fluid Dynamics
Many industrial materials—like suspensions and slurries—can be characterized as a viscoplastic fluid where the material behaves like a solid if the applied stress is below the characteristic yield stress of the material and flows if it exceeds it. Materials with these properties are often referred to as Bingham plastics or Bingham fluids, and include common everyday items like bread dough, toothpaste, and even chocolate.
One of the well-known models used to describe the constitutive relation for viscoplastic materials is the Papanastasiou model in which a smooth transition in the shear stress-strain rate curve is embedded in the model to circumvent the discontinuity at the onset of motion.
This figure shows the predicted loss coefficient of a Bingham fluid flowing through a sudden contraction (3-inch to 2-inch) as a function of the modified Reynolds number; superimposed on the graph are the velocity magnitude contours for different consistency indices, K. As the consistency index increases, the pressure drop increases and the plug flow velocity also increases, which is accompanied by a decrease in the plug flow region. The determination of the yielded vs. un-yielded regions in the flow, especially for complex 3D geometries, is an important parameter for design considerations and can be easily predicted with a CFD simulation.