# Scalar Transport in T-Junction Pipe

## Overview

The purpose of this numerical simulation is to validate the following parameters of incompressible Single Phase Scalar Transport in a T-junction pipe:

• Scalar mixing distribution in the mixing 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 [1] [2]. The flow regime selected for the study has a Reynolds number of Re=24900

$Re=24900$

.

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## Geometry

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
Value [m] 25D

$25D$

12D

$12D$

12.5D

$12.5D$

0.05

$0.05$

## Domain and Analysis type

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 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
Snappy-Hex-Mesh 4100268 3D hexahedral

The numerical analysis performed is detailed as follows:

Tool Type : OPENFOAM®

Analysis Type : Steady-State Passive Scalar Transport

Turbulence Model : K-Omega SST

## Simulation Setup

Fluid:

• Water :
• Kinematic viscosity (ν
$\nu$

=1.004×106[m²/s]

$=1.004×{10}^{-6}\left[m²/s\right]$

• Diffusion coefficient =2.3×109[m²/s]
$=2.3×{10}^{-9}\left[m²/s\right]$

• Turbulent Schmidt number =0.25
$=0.25$

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 ms1

Outlet Zero Gradient Fixed Value: 0 Pa

Wall no-slip Fixed Value: 0.0 ms1

Symmetry

## Results

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.3A-D. 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 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

## References

 [1] Zboray , A. Manera, B. Niceno , H.-M. Prasser : “Investigations on Mixing Phenomena in Single-phase Flows in a T-Junction Geometry”, The 12th Int. Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-12), Sheraton Station Square, Pittsburgh,Pennsylvania, U.S.A. September 30-October 4, 2007, Paper No. 71, pp. 1-20.
 [2] 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”.

## 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.