Aorta: Pulsatile Blood Flow

Aorta, Non-Newtonian Pulsating Blood Flow — ANSYS Fluent CFD Simulation

Description

This project studies non-Newtonian pulsating blood flow in the aorta using ANSYS Fluent. The aorta geometry is obtained from a real CT scan, provided as an STL file that must be repaired before meshing — a workflow representative of patient-specific biomedical CFD. Blood is a non-Newtonian fluid whose apparent viscosity changes with shear rate, and the aorta's pulsatile flow, curvature, and branching make it a rich, realistic case for studying how such a fluid behaves in a large vessel. Within the Non-Newtonian Flow: Beginner CFD Training Package, this project builds on the earlier blood-flow case by moving to a larger, geometrically complex vessel reconstructed from real medical imaging.

Methodology

The aorta geometry is obtained from a CT scan, and tools such as SpaceClaim, ICEM CFD, and Design Modeler can be used to repair it; here ICEM CFD was used to fix the geometry and generate the mesh. The mesh was first generated with the octree method using five layers of prism cells at a ratio of 1.2, then improved with the Delaunay method, giving a final count of 457,864 cells. A UDF defines the pulsatile inlet velocity. The non-Newtonian behavior of blood is captured with the Carreau model, in which viscosity depends on the shear rate, defined by the zero-shear viscosity (µ₀), the infinite-shear viscosity (µ∞), the power index (n), and the relaxation time (λ). No energy equation is included, so temperature is neglected. The solver is transient, the flow is turbulent, and the density is constant at 1060 kg/m³, with a no-slip condition on the inner surface of the vessel wall. The UDF used to define the pulsating inlet velocity is provided.

Analysis

The results illustrate the inlet velocity and pressure drop over the pulse cycle, with the maximum velocity occurring at 0.15 s. The wall shear stress (WSS) contours show the maximum values in the aorta sections of smaller diameter, while the static-pressure contours show that at the beginning of the blood pumping, the pressure is highest at the entrance of the branches. When suction occurs at 0.4 s, it has the greatest impact on the inlet section of the aorta. Animation files of pressure and shear stress are included to reveal the pulsatile behavior and give a clearer understanding of the flow. By the end of this project, you'll be able to repair a real STL geometry from medical imaging, generate a prism-layer mesh, apply the Carreau non-Newtonian model with a UDF-defined pulsatile inlet, and interpret the velocity, pressure, and wall-shear-stress fields that characterize pulsatile blood flow in the aorta.