Blood Flow - CFD Simulation SimFlow Tutorial

This tutorial focuses on a non-Newtonian fluid, specifically modeling blood using the Bird-Carreau transport model. We will use a time-variable inlet velocity profile to map the heart rate. Additionally, we will showcase the post-computation process of calculating wall shear stress and visualizing it through ParaView.

SimFlow is a general purpose CFD Software

To follow this tutorial, you will need SimFlow free version, you may download it via the following link:
Download SimFlow

Open SimFlow and create a new case named blood_flow

Firstly, we need to Download GeometriesInletOutlet01Outlet02Wall

The STL format does not contain the unit information which are defined during the geometry export. If we do not know the exported unit, we can estimate it based on the total size of imported geometries. The size is displayed next to Geometry size label. In our case, the default unit meter is correct.

After importing geometry it will appear in the 3D window.

We will change the color of the wall to distinguish it from the other geometries.

In the Hex Meshing panel, we will change meshing properties associated with geometry objects. We want to apply the same settings to all geometries. We will set the parameters for the first surface and copy the configuration to the remaining geometries.

We want to apply the same settings to all geometries. We will copy the configuration from the inlet to the remaining geometries.

Under the Base tab we will define the domain of the background mesh.

Material Point tells the meshing algorithm on which side of the geometry the mesh is to be retained. Since we are considering flow inside the blood vessel we need to place the material point inside the geometry.

You can specify the point location from the 3D view. Hold the CTRL key and drag the arrows to the destination.

Everything is now set up for meshing

After the meshing process, the mesh will appear in the graphics window. Use the scroll wheel in your mouse to zoom into the model.

Check the mesh quality and statistics.

We want to analyze the transient, incompressible flow with non-newtonian fluid to model the blood flow. For this purpose, we will use the pimpleFoam solver.

Due to the small diameter of the vessel and high viscosity of the fluid, it can be assumed that the flow remains laminar.

For the demonstration purpose, we will model the blood as non-newtonian fluid using the Bird-Carreu model. We will operate on quantities divided by density and we do not need to specify the density. However, we have to take this fact into account during postprocessing.

The flow in the blood vessels is oscillatory in time. We will define the inlet velocity using the time history of one oscillation period. To do so we will use a table input option. The rest of the boundaries conditions we will leave as default.

We will use a predefined velocity profile from the external file.
We need to Download Velocity Profileprofile.csv and import it to the Simflow.

Before we start simulation we need to define the flow state at the time zero. We will specify a constant velocity equal to ` 0.2 m/s ` which corresponds to the initial inlet velocity.

We would like to monitor flow velocity at the outlet boundaries. The results can be later on used to calculate the volumetric and mass flow rates for each outlet.

We will set the time of simulation to match the inlet velocity time range. We also want the solver to automatically determine the proper time step. This should lead to good stability and potentially reduce simulation time.

We can control how often results should be saved on the hard drive. We will write the results at the interval of ` 0.02 ` seconds. Note, that only saved data will be available during postprocessing.

To speed up the calculation process increase the number of CPUs basing on your PC capability. We recommend using at least 4 cores for this tutorial. The free version allows you to use only 2 processors in parallel mode. To get the full version, you can use the contact form to Request 30-day Trial

Estimated computation time for 2 processors: 1 hour

Outlet boundary monitors are ploted on the charts next to Residual tab.

Calculations are finished, but before we start postprocessing, we will calculate wall shear stress (WSS). It can be calculated as the multiplication of dynamic viscosity and velocity gradient next to the wall. WSS is a characteristic value in medicine, used for circulatory system disease identification. Too low values are the indicators of atherosclerosis while the large WSS leads to the thickening of the vessel wall and increasing its diameter. This occurs when one vessel splits into two like in our example.

After computations are finished we can do complex visualization of our results with ParaView.

Load the results into the program.

ParaView skips the initial time step by default, therefore we need to add the zero time to simulation.

To get the true value of the wall shear stress we need to multiply SimFlow results by the density. Please remember that for the sake of this tutorial we have created coarse mesh. We also model the vessel as rigid walls, whereas in reality, it’s hyper-elastic. Nevertheless, still we can identify the regions of extremely high and low wall shear stresses.

Finally, we can take a look at streamlines.

To show the geometry together with the streamlines we will follow these steps: