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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 \(Re = 40\).

Import validation project into workspace

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.

Non-Newtonian-geometry

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
Non-Newtonian-mesh

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): \(k [m^2/s]\) based on \(Re=40\)
  • Flow/Power Index \(n = 0.5 - 2\ \)

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: \(0.5\ ms^{-1}\) Zero Gradient
Outlet Zero Gradient Fixed Value: \(0\ Pa\)
Wall no-slip Fixed Value: \(0.0\ ms^{-1}\) Zero Gradient
Custom 2D Empty 2D Empty

Results

The numerical simulation results for the various Power Index ranging from \(n = 0.5 - 2\) for a \(Re=40\) 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: \(Re=\frac{\rho\ V^{2-n} H^{n} }{K}\)

where, \(\rho\) is the density, \(V\) is the flow inlet velocity, \(H\) is the inlet height, \(n\) is the power index and \(K\) 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 \(X = 28\) is shown in fig.3. The figure shows the normalized velocity profile along the normalized channel height for \(n > 1\) shear thickening or dilatant fluid (e.g corn starch water), \(n = 1\) Newtonian fluid and \(n < 1\) Shear thinning or pseudoplastic fluids (e.g ketchup, paint, blood).

Non-Newtonian-results-comparison

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 \(n = 0.5, 1.0, 2.0\) are shown in the figure Fig.4 below.

Non-Newtonian-results-velocity

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

References

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