7.3.6 Inlet Vent Boundary Conditions

Inlet vent boundary conditions are used to model an inlet vent with a specified loss coefficient, flow direction, and ambient (inlet) pressure and temperature.

Inputs at Inlet Vent Boundaries

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

• type of reference frame

• total (stagnation) pressure

• total (stagnation) temperature

• flow direction

• static pressure

• turbulence parameters (for turbulent calculations)

• radiation parameters (for calculations using the P-1 model, the DTRM, the DO model, or the surface-to-surface model)

• chemical species mass or mole fractions (for species calculations)

• mixture fraction and variance (for non-premixed or partially premixed combustion calculations)

• progress variable (for premixed or partially premixed combustion calculations)

• discrete phase boundary conditions (for discrete phase calculations)

• multiphase boundary conditions (for general multiphase calculations)

• loss coefficient

• open channel flow parameters (for open channel flow calculations using the VOF multiphase model)

All values are entered in the Inlet Vent dialog box (Figure  7.3.5), which is opened from the Boundary Conditions task page (as described in Section  7.1.4).

The first 12 items listed above are specified in the same way that they are specified at pressure inlet boundaries. See Section  7.3.3 for details. Specification of the loss coefficient is described here. Open channel boundary condition inputs are described in Section  24.3.1.

Figure 7.3.5: The Inlet Vent Dialog Box

Specifying the Loss Coefficient

An inlet 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 that you supply. That is, the pressure drop, $\Delta p$, varies with the normal component of velocity through the vent, $v$, as follows:

where $\rho$ is the fluid density, and $k_L$ is the non-dimensional 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 the Loss-Coefficient across the vent as a constant, polynomial, piecewise-linear, or piecewise-polynomial function of the normal velocity. The dialog boxes for defining these functions are the same as those used for defining temperature-dependent properties. See Section  8.2 for details.