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7.10.3 Mass Flow Split Boundary Conditions

In FLUENT, it is possible to use multiple outflow boundaries and specify the fractional flow rate through each boundary. In the Outflow panel, set the Flow Rate Weighting to indicate what portion of the outflow is through the boundary.

Figure 7.10.2: The Outflow Panel
figure

The Flow Rate Weighting is a weighting factor:


 \begin{array}{c} \mbox{percentage flow} \\ \mbox{through bou... ...boundary}} {\mbox{sum of all {\textbf{Flow Rate Weighting}}s}} (7.10-1)

By default, the Flow Rate Weighting for all outflow boundaries is set to 1. If the flow is divided equally among all of your outflow boundaries (or if you have just one outflow boundary), you need not change the settings from the default; FLUENT will scale the flow rate fractions to obtain equal fractions through all outflow boundaries. Thus, if you have two outflow boundaries and you want half of the flow to exit through each one, no inputs are required from you. If, however, you want 75% of the flow to exit through one, and 25% through the other, you will need to explicitly specify both Flow Rate Weightings, i.e., 0.75 for one boundary and 0.25 for the other.

figure   

If you specify a Flow Rate Weighting of 0.75 at the first exit and leave the default Flow Rate Weighting (1.0) at the second exit, then the flow through each boundary will be


Boundary 1 = $\frac{0.75}{0.75+1.0} $ = 0.429 or 42.9%
     
Boundary 2 = $\frac{1.0}{0.75+1.0}$ = 0.571 or 57.1%


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