The purpose of this numerical simulation is to validate the following parameters of incompressible Single Phase Scalar Transport in a T-junction pipe:
The numerical simulation were carried out using the Reynolds-Averaged Navier–Stokes (RANS) approach with Turbulence modelling. The results of SimScale were compared with the experimental results shown in  . The flow regime selected for the study has a Reynolds number of
The geometry of the study is a T-junction 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|
The domain is the internal region of the T-junction 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 T-junction in both main and branch pipes. For the near wall treatment, no wall-functions were used and the mesh is based on a y-plus (y+) criterion of
near the walls. The details of the mesh are listed in the following table:
Mesh and Element types :
|Mesh type||Number of nodes||Type|
The numerical analysis performed is detailed as follows:
Tool Type : OPENFOAM®
Analysis Type : Steady-State Passive Scalar Transport
Turbulence Model : K-Omega SST
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.
|Inlet||Turbulent Fixed Value:
|Outlet||Zero Gradient||Fixed Value:
|Wall no-slip||Fixed Value:
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 , and also mentioned in . 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.3A-D. The figures show the scalar distribution at four downstream location in the mixing pipe of
. 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 cross-sectional and stream-wise planes in the mixing pipe by Fig.5A and Fig.5B.
Fig.5. Flow field along stream-wise and cross-sectional directions
|||Th. Frank, M. Adlakha, C. Lifante, H.-M. Prasser, F. Menter, “SIMULATION OF TURBULENT AND THERMAL MIXING IN T-JUNCTIONS USING URANS AND SCALE-RESOLVING TURBULENCE MODELS IN ANSYS CFX”.|
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