NEWTONIAN VS NON NEWTONIAN FLUIDS

Ever wondered why some liquids flow easily while others behave strangely? In the world of Fluid Dynamics, understanding the difference between Newtonian and Non-Newtonian fluids is critical for accurate simulations. While Newtonian fluids like water maintain constant viscosity, fluids like human blood are complex—their viscosity changes depending on the force applied.

In this tutorial, we analyze the Non-Newtonian Blood Flow through a Stenosed Pipe using ANSYS Fluent. We explore how blood behaves as a shear-thinning fluid and observe the sharp viscosity drops in constricted passages.

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Project Overview

The simulation focuses on a stenosed pipe (a pipe with a constriction) to mimic a blood vessel with a blockage. We aim to find the flow velocity and observe changes in the molecular viscosity of the blood as it passes through the throat of the stenosis.

1. Geometry Creation (DesignModeler)

• Dimensions: Total pipe length of 50mm.
• Stenosis: A 10mm middle section with a minimum diameter of 0.5mm.
• Method: We use the Polyline tool in the YZ Plane to draw the half-profile and then Revolve it around the G-axis to create the 3D volume.

2. Meshing & Quality Check

A structured mesh is vital for capturing gradients near the wall.

• Sizing: We applied edge sizing to the circular edges with 100 divisions.
• Quality: Checked the Skewness and Aspect Ratio to ensure the cells stay within the student version limits for stability.

3. Solver Setup (ANSYS Fluent)

Since blood flow in small vessels is typically slow, we use the Laminar Viscous Model with Double Precision.

Material Properties: The Carreau Model

Because blood is not in the standard database, we modify 'water-liquid' with the following Carreau Model parameters:

• Density: 1050 kg/m³
• Time Constant: 3.313 s
• Power Index: 0.3568
• Zero Viscosity: 0.056 Pa·s
• Infinite Viscosity: 0.00345 Pa·s

4. Boundary Conditions

• Inlet: Velocity Inlet of 0.01 m/s.
• Outlet: Default Pressure Outlet.
• Initialization: Hybrid Initialization with 500-600 iterations for convergence.

Results & Analysis

The post-processing results reveal a fascinating inverse relationship between the shear rate and viscosity:

1. Center Region: Higher viscosity occurs near the center where the shear rate is low.
2. Near Walls: Viscosity is lower near the pipe walls due to higher velocity gradients.
3. The Stenosis Throat: As the diameter reduces, flow accelerates significantly. This causes high shear rates, leading to a sharp drop in viscosity—confirming the shear-thinning behavior of blood.

WATCH THE FULL STEP-BY-STEP TUTORIAL ON THE ANSYS TUTOR YOUTUBE CHANNEL

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