Injection region settings are described in Injection Regions in the CFX-Pre User's Guide.

Modeling information is provided in Modeling Blade Film Cooling with Injection Regions in the CFX-Solver Modeling Guide.

Injection regions function in a very similar way to the equivalent inlet or outlet boundary condition. As such, in the limit of a fine mesh, they should have identical behavior. For details on the available options, see Inlet (Subsonic) and Outlet (Subsonic).

When the fluid is compressible, injection regions normally operate in the subsonic regime. However, if the mass flow rate is sufficiently high then sonic flow choking might occur if the hole/slot is modeled in detail. In such circumstances, you might want to activate the Sonic Limiter option. For details, see Flow Regime in the CFX-Pre User's Guide.

Information about post-processing injection regions in CFD-Post is provided in Injection Regions in the CFD-Post User's Guide.

Local Pressure option for Sonic Limiter

Here, the fluid is assumed to behave like an ideal gas, and the isentropic relationship between the Mach number and the mass flow rate can be exploited:

(1–267)

where:

By setting the limiting Mach number to 1.0, the given mass flow and area of the hole/slot can be used to find an appropriate pressure to apply locally at the hole/slot. Applying such pressure has the effect of increasing the local density, thereby limiting the flow speed and solution Mach number.