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Non-Newtonian Flow Through Expansion Channel

Overview

The purpose of this numerical simulation is to validate the flow velocity profile for a Non-Newtonian fluid via the Power-Law model.

The numerical simulation were carried out using the Reynolds-Averaged Navier–Stokes (RANS) approach at laminar flow conditions. The results of SimScale simulation runs were compared to the analytical results shown in [1] [2]. The flow regime selected for the study has a Reynolds number of Re=40

Re=40

.

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Geometry

The geometry of the study is a 2 dimensional channel with a 3:1 expansion (see Fig.1.). A brief description of the dimensions are provided by the table below.

Fig.1. Geometry of the 3:1 Expansion channel
  • with respect to expansion step.

Domain and Analysis type

The domain is the internal region of the geometry with the domain extents same as the geometrical dimensions. For this study a full hexahedral structured mesh was created with the “blockMesh” open-source tool (see Fig.2.). The Mesh was refined at the expansion step in both horizontal and vertical directions. Two meshes, mesh M_2 (intermediate) and mesh M_3 (fine) were used for the study to check for mesh independence of results. The details of the mesh are listed in the following table:

Mesh and Element types :

Mesh type Number of cells Type
blockMesh 30.7 – 77.6 thousand 3D hexahedral
Fig.2. Expansion channel mesh used for the SimScale case

The numerical analysis performed is detailed as follows:

Tool Type : OPENFOAM®

Analysis Type : In-Compressible Steady-State

Turbulence Model : Laminar

Non-Newtonian model : Power-Law

Simulation Setup

Fluid:

Non-Newtonian

  • normalized Consistancy Index (by density): k[m2/s]
    k[m2/s]

     

    based on Re=40

    Re=40

     

  • Flow/Power Index n=0.52 
    n=0.52 

     

Boundary Conditions:

For the inlet boundary, a fixed velocity condition was applied, while a pressure boundary condition was applied at the outlet. No-slip condition was applied for the walls and empty condition for the side faces. The following table provides the further details.

Boundary type Velocity Pressure
Inlet laminar Fixed Value: 0.5 ms1

0.5 ms1

 

Zero Gradient
Outlet Zero Gradient Fixed Value: 0 Pa

0 Pa

 

Wall no-slip Fixed Value: 0.0 ms1

0.0 ms1

 

Zero Gradient
Custom 2D Empty 2D Empty

Results

The numerical simulation results for the various Power Index ranging from n=0.52

n=0.52

 for a Re=40

Re=40

 are compared with analytical formulation given by Tanner [1] and shown by [2]. The formulations for the Generalized Reynolds number for non-Newtonian flows for this case is as follows:

Generalized Reynolds number: Re=ρ V2nHnK

Re=ρ V2nHnK

 

where, ρ

ρ

 is the density, V

V

 is the flow inlet velocity, H

H

 is the inlet height, n

n

 is the power index and K

K

 is the consistency factor. All quantities here are in standard S.I units.

Two meshes M_2 and M_3 were analyzed. As no further improvement was observed for mesh M_3 the results presented are for mesh M_2. A comparison of the velocity profile in the fully developed region downstream of the expansion at X=28

X=28

 is shown in fig.3. The figure shows the normalized velocity profile along the normalized channel height for n>1

n>1

 shear thickening or dilatant fluid (e.g corn starch water), n=1

n=1

 Newtonian fluid and n<1

n<1

 Shear thinning or pseudoplastic fluids (e.g ketchup, paint, blood).

Fig.3. Result comparison of numerical and analytical data. Normalized velocity profile along channel height at x=28.

The Velocity contours with streamlines and corresponding profiles for Power Index n=0.5,1.0,2.0

n=0.5,1.0,2.0

 are shown in the figure Fig.4 below.

Fig.4. Mean velocity contours with streamlines and profiles for n = 0.5, 1.0 and 2.0.

References

[1] (12)

    1. Tanner, “Engineering Rheology”, Oxford University Press, Oxford, 1992.
[2] (12)

  1. MANICA, A.L. de BORTOLI, “Simulation of Incompressible Non-Newtonian Flows Through Channels with Sudden Expansion Using the Power-Law Model”.

Disclaimer

This offering is not approved or endorsed by OpenCFD Limited, producer and distributor of the OpenFOAM software and owner of the OPENFOAM® and OpenCFD® trade marks. OPENFOAM® is a registered trade mark of OpenCFD Limited, producer and distributor of the OpenFOAM software.

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