# Description AC3-10

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# Combining/dividing flow in Y junction

## Introduction

This application challenge focuses on the prediction of pressure losses and head loss coefficients for water flowing in a ‘Y’ junction. A series of tests has been carried out under both convergent and divergent flow conditions, and at various splits of flow in the two minor branches. The flow rates used in the major branch covered an approximate Reynolds number range of ${\displaystyle 5x10^{5}}$ to ${\displaystyle 1.2x10^{6}}$.

The ‘Y’ junction has an included angle of 50 degrees between the two minor branches, and the internal geometry has been optimised.

## Relevance to Industrial Sector

Flow behaviour in pipe junctions is relevant to many industrial applications. At certain flow rate ratios the pressures in the ‘Y’ junction give rise to ‘negative’ differential pressures. CFD can provide an insight into the reasons behind this.

## Design or Assessment Parameters

In this application challenge the design or assessment parameters DOAPs, are the differential pressures between the legs of the ‘Y’ junction.

## Flow Domain Geometry

The flow geometry is shown in Figures 1 to 5.

## Flow Physics and Fluid Dynamics Data

The flow is turbulent, weakly compressible, and isothermal. The Reynolds number in the major pipe branch ranges from 5x105 to 1.2x106. The fluid dynamics data (except boundary conditions) which are necessary in order to set up a CFD simulation are specified below:

The water density is calculated from the equation:

${\displaystyle \rho _{w}=1.0012\times {(1000.25-0.008{t}-0.004{t}^{2}+0.46\times 10^{-6}P)}\quad (1)}$

The water viscosity is calculated from the equation:

${\displaystyle \ln \mu _{w}={(484.1/{(120.57+t)})}-10.35\qquad \qquad \qquad \qquad \qquad \quad (2)}$

Reynolds numbers are based on the diameter of branch 1 (with the combined flow rates) and are defined as:

${\displaystyle Re_{D}=\rho _{w}v_{1}D_{1}/\mu _{w}\qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad \quad (3)}$