Blood Vessel (FSI) with the Pulse Velocity, CFD Simulation Ansys Fluent Training

Description

In this project, we present a simulation of a Blood Vessel via ANSYS Fluent software.

Since the vessel is exposed to blood flow, an interaction occurs between the blood flowing and the vessel structure. First, the blood flow exerts a force on the vessel's body by hitting it. Subsequently, displacement or deformation appears on the vessel, which can lead to the blood flow being affected. Therefore, we intend to perform a numerical simulation of the blood vessel as a Fluid-Structure Interaction (called FSI).

The interaction between fluid and structure can be implemented as:

• One-way FSI

• Two-way FSI

In this project, we aim to analyze both the effect of fluid on the structure and the effect of the structure on the fluid. So, we choose Two-way FSI, which is a more accurate and realistic but more complex approach.

We modeled the geometry via Spaceclaim software. The computational domain is a sample space of a vascular system with a simple construction. We considered the blood vessel as a horizontal cylinder with a solid layer surrounding the fluid region.

We meshed the computational domain via ANSYS Meshing software. The mesh is of an unstructured type, and approximately 56,000 cells have been generated.

Methodology

Fluid-structure interaction can be performed in two general methodologies:

• In the ANSYS Workbench environment, using an external solver (specifically, system coupling)

• Only in the Fluent solver (in the form of an intrinsic FSI).

In this project, we implemented a two-way FSI in the ANSYS Fluent environment. In other words, the Fluent solver performs both fluid and solid calculations simultaneously.

For two-way FSI in Fluent solver, the Structure model is utilized. The structural model can be implemented in two ways:

• Linear elasticity: The deformation is proportional to the applied force. In this case, the deformations are usually small, and the calculation process is faster.

• Nonlinear elasticity: The deformation is not necessarily proportional to the applied force. In this case, the deformations are usually large, and the calculation process is more complex and time-consuming.

In this project, we considered fluid-structure interaction in the form of a Linear Elasticity state.

Since we were analyzing two-way FSI and considering the effect of structural displacement on the adjacent fluid, we used the Dynamic Mesh model. In other words, we establish a connection between the fluid and structural calculations with the Intrinsic FSI option. Then, we enabled the smoothing and remeshing methods to define a deformable mesh.

In addition, for defining blood flow in a pulse-mode, we used a user-defined function (UDF) so that the flow has a variable velocity with respect to time.

Results

We analyzed the results in two fluid and solid approaches:

In a fluid view, we studied the behavior of blood flow. For this, we obtained the distributions of the pressure and velocity of blood. The results show that the blood flow collides with the vessel body at pulsatile speed and, as a result, exerts a hydraulic force on the vessel structure.

In a solid view, we studied the behavior of the vessel body under the influence of the applied forces of the blood flow. For this, we obtained the distribution of the von Mises stress and displacements (in all directions). The results confirm that the blood flow affects the vessel structure and, as a result, it undergoes deformation relative to the initial state.

In conclusion, we can claim that we carried out the simulation project of a blood vessel correctly and acceptably by using the two-way FSI method.