Non Newtonian Blood Pulse Flow in a Vein, ANSYS Fluent CFD Training

Description

This simulation is about non-newtonian blood pulse flow in a vein via ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis.

The fluid used in this simulation is blood, a non-Newtonian fluid. Non-Newtonian fluids are fluids whose viscosity varies with their reaction rate, meaning they lack a specific viscosity.

In this type of fluid, the relationship between the shear stress variations and the applied stress rates is nonlinear; therefore, there is no constant coefficient of fit for viscosity. We do this transient simulation for 0.5 s. By the way, we apply a User-Defined Function (UDF) to model the pulse of the blood flow.

Since blood flow doesn’t have constant velocity and pulsed, the velocity function must be used periodically using the User-Defined Function code.

The geometry of the present model is drawn by Gambit software. The present model consists of a cylindrical vessel and two smaller vessels with a smaller size and diameter, such that one branch has a 90-degree angle and the other, a branch with a 45-degree curvature.

The present model consists of one input section and two output sections.

The model is then meshed by ANSYS Meshing software. The model mesh is unstructured, and 397388 cells have been created.

Non Newtonian Blood Method

Since the fluid used in this simulation is blood at a density of 1050 kg/m³ and blood is a Non-Newtonian fluid type, the Carreau equation with certain parameters has been used.

Newtonian fluids generally have constant viscosity during force application, but non-Newtonian fluids have variable viscosity during force application, which has different types.

Time-dependent non-Newtonian fluids have two categories: Rheopectic, such as printer ink and cream, which increase their viscosity over time, and Thixotropic, such as honey, whose viscosity decrease when the force is applied.

Time-independent non-Newtonian fluids are also divided into three groups: Dilatants such as starch and clay, whose viscosity depends only on the force value applied, and Pseudoplastic, such as greases, paints, soaps, and ketchup, which are inversely correlated with the force value applied.

Other groups called Bingham, such as toothpaste and silica nanocomposites, have a stress threshold or a certain amount of force and tension to flow. In the present simulation, blood is used as a Pseudoplasticity non-Newtonian fluid defined by the Carreau model.

This model attempts to create a wide range of fluids by establishing a curve commensurate with the Newtonian and non-Newtonian fluid functions of the type of subtractive stress (Pseudoplasticity).

Non Newtonian Blood Conclusion

After simulation, the contours of pressure and wall shear stress are obtained at different times. The results show that the flow inside the vessel is completely pulsatile; Because the pressure changes at different times.

Also, the results show that the pressure corresponds to the wall shear stress. An increase in pressure inside the vessel leads to an increase in the wall shear stress.