The purpose of this numerical simulation is to validate the following parameters of incompressible Single Phase Scalar Transport in a Tjunction pipe:
The numerical simulation were carried out using the ReynoldsAveraged Navier–Stokes (RANS) approach with Turbulence modelling. The results of SimScale were compared with the experimental results shown in [1] [2]. The flow regime selected for the study has a Reynolds number of Re=24900
$Re=24900$.
Import validation project into workspace
The geometry of the study is a Tjunction cylindrical pipe system (see Fig.1.). A brief description of the dimensions is provided by the table below.
Main Pipe Length  Branch Pipe Length  Mixing Pipe Length  Diameter  

Value [m]  25D
$25D$

12D
$12D$

12.5D
$12.5D$

0.05
$0.05$

The domain is the internal region of the Tjunction pipe with the domain extents same as the geometrical dimensions. Based on the flow physics and the geometry, a symmetry condition was applied to reduce the domain size and computational time. For this study a hexahedral mesh was created with the “Snappy Hex Mesh” on the SimScale platform (see Fig.2.). The Mesh was refined at the Tjunction in both main and branch pipes. For the near wall treatment, no wallfunctions were used and the mesh is based on a yplus (y+) criterion of y+<1
${y}^{+}<1$near the walls. The details of the mesh are listed in the following table:
Mesh and Element types :
Mesh type  Number of nodes  Type 

SnappyHexMesh  4100268  3D hexahedral 
The numerical analysis performed is detailed as follows:
Tool Type : OPENFOAM®
Analysis Type : SteadyState Passive Scalar Transport
Turbulence Model : KOmega SST
Fluid:
) =1.004×10−6[m²/s]
$=1.004\times {10}^{6}[m\xb2/s]$
Boundary Conditions:
For the inlet boundary, a turbulent fixed velocity condition was applied, while a pressure boundary condition was applied at the outlet. At the main inlet the scalar value was set to 1 and at the branch inlet a value of 0 was set. The following table provides the further details.
Boundary type  Velocity  Pressure 

Inlet  Turbulent Fixed Value: 0.5 ms−1
$0.5\text{}m{s}^{1}$

Zero Gradient 
Outlet  Zero Gradient  Fixed Value: 0 Pa
$0\text{}Pa$

Wall noslip  Fixed Value: 0.0 ms−1
$0.0\text{}m{s}^{1}$

Zero Gradient 
Symmetry 
The numerical simulation results for the mixing scalar are compared with experimental data provided by the Laboratory for Nuclear Energy Systems, Institute for Energy Technology (ETHZ), Zürich [1], and also mentioned in [2]. For this validation the experimental data corresponds to ETHZ test No.14.
A comparison of the mixing scalar distribution obtained with SimScale and experimental results is given in Fig.3AD. The figures show the scalar distribution at four downstream location in the mixing pipe of 51,91,191,311mm
$51,91,191,311mm$. The noted variations in results are believed to be due to anisotropic turbulence effects. These effects may be captured more accurately by higher order turbulence models.
Fig.3. Scalar distribution comparison at downstream locations in mixing pipe.
The scalar distribution contours at downstream locations in the mixing pipe are shown in the figures Fig.4A and Fig.4B below.
A visualization of the flow field is shown along the crosssectional and streamwise planes in the mixing pipe by Fig.5A and Fig.5B.
Fig.5. Flow field along streamwise and crosssectional directions
[1] 

[2]  Th. Frank, M. Adlakha, C. Lifante, H.M. Prasser, F. Menter, “SIMULATION OF TURBULENT AND THERMAL MIXING IN TJUNCTIONS USING URANS AND SCALERESOLVING TURBULENCE MODELS IN ANSYS CFX”. 
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