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7.11.1 Inputs at Outlet Vent Boundaries

You will enter the following information for an outlet vent boundary:

All values are entered in the Outlet Vent panel (Figure  7.11.1), which is opened from the Boundary Conditions panel (as described in Section  7.1.4).

The first 4 items listed above are specified in the same way that they are specified at pressure outlet boundaries. See Section  7.8.1 for details. Specification of the loss coefficient is described here. Open channel boundary condition inputs are described in Section  23.10.2.

Figure 7.11.1: The Outlet Vent Panel

Specifying the Loss Coefficient

An outlet vent is considered to be infinitely thin, and the pressure drop through the vent is assumed to be proportional to the dynamic head of the fluid, with an empirically determined loss coefficient which you supply. That is, the pressure drop, $\Delta p$, varies with the normal component of velocity through the vent, $v$, as follows:

 \Delta p = k_L \frac{1}{2} \rho v^2 (7.11-1)

where $\rho$ is the fluid density, and $k_L$ is the nondimensional loss coefficient.


$\Delta p$ is the pressure drop in the direction of the flow; therefore the vent will appear as a resistance even in the case of backflow.

You can define a constant, polynomial, piecewise-linear, or piecewise-polynomial function for the Loss-Coefficient across the vent. The panels for defining these functions are the same as those used for defining temperature-dependent properties. See Section  8.2 for details.

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