Orifice

The geometry of the orifice fluid section is shown in Figure 76. It is characterized by the following constants (to be specified in that order on the line beneath the *FLUID SECTION card):

Figure 76: Geometry of the orifice fluid section

• the cross section $A$.
• the orifice diameter $d$.
• the length $L$.
• the inlet corner radius $r$.
• the inlet corner angle $\alpha$.
• the orifice-to-upstream pipe diameter ratio $\beta=d/D$.
• the rotational velocity $v$, if the orifice is part of a rotating structure.
• a reference network element.

Depending on the orifice geometry, an inlet corner radius or an inlet corner angle (chamfered inlet) should be selected. They are mutually exclusive. The corrections for a chamfered inlet are taken from [27].

The last constant, i.e. the number of a reference network element, is necessary in case a rotating structure is preceded by a network element which diverts the upstream air velocity from the axial direction (such as a preswirl nozzle). In that case, the rotational velocity of the orifice has to be corrected by the circumferential component of the velocity at the exit of the preceding element.

The calculation of the discharge coefficient $C_d$ can be performed according to different formulas. This is selected by the TYPE parameter:

• TYPE=ORIFICE_CD1 or just TYPE=ORIFICE: $C_d=1$.
• TYPE=ORIFICE_MS_MS: Basis formula by McGreehan and Schotsch, rotational correction by McGreehan and Schotsch [43].
• TYPE=ORIFICE_PK_MS: Basis formula by Parker and Kercher [54], rotational correction by McGreehan and Schotsch [43].

Example files: linearnet, vortex1.