Orifice
Fixed orifice
Description
Equations
Variables
Connections
Parameters
The Orifice component models a sharp-edge orifice with a circular opening of a given area.
Formulation Approaches
One of two approaches can be selected for modeling the flow in the device. When the boolean parameter Use constant Cd is true, a constant coefficient of discharge (Cd) is used, otherwise a variable coefficient of discharge with maximum value (Cd⁡max) and a critical flow number (Critno) are used.
Optional Volumes
The boolean parameters Use volume A and Use volume B, when true, add optional volumes VA and VB to ports A and B, respectively. See Port Volumes for details.
If two orifices or valves are connected, enabling a volume at the common port reduces the stiffness of the system and improves the solvability.
p=pA−pB
Acs=A
Orifice Fluid Equations
{p=π4⁢ρ⁢ν⁢qCd2⁢Acs⁢π⁢Acs⁢16⁢q4π2⁢Acs2⁢ν4+ReCr414Use constant Cd=trueq=Cd⁡max⁢tanh⁡4⁢Acsπ⁢2⁢pρν⁢Critno⁢Acs⁢2⁢pρ⁢sign⁡potherwise
Optional Volume Equations
VfA={Va⁢1+pAElUse volume A=true0otherwiseVfB={Vb⁢1+pBElUse volume B=true0otherwise
q=qA−qVA=−qB−qVB
qVA={dVfAdtUse volume A=true0otherwiseqVB={dVfBdtUse volume B=true0otherwise
Name
Units
Modelica ID
p
Pa
Pressure drop from A to B
pX
Pressure at port X
q
m3s
Flow rate from A to B
qX
Flow into port X
qVX
Flow rate into port X's optional volume
VfX
m3
Effective volume at port X
portA
Upstream hydraulic port
portB
Downstream hydraulic port
General
Default
A
1·10−6
m2
Area of opening
Use constant Cd
true
True (checked) means a constant coefficient of discharge is implemented, otherwise a variable Cd is used in flow calculation
UseConstantCd
Cd
0.7
Flow-discharge coefficient; used when Use constant Cd is true
ReCr
12
Reynolds number at critical flow; used when Use constant Cd is true
Coeff
Maximum flow-discharge coefficient; used when Use constant Cd is false
Critno
1000
Critical flow number; used when Use constant Cd is false
Crit_no
Use volume A
false
True (checked) means a hydraulic volume chamber is added to portA
useVolumeA
VA
Volume of chamber A
Va
Use volume B
True (checked) means a hydraulic volume chamber is added to portB
useVolumeB
VB
Volume of chamber B
Vb
For more information see Port Volumes.
Fluid Parameters
The following parameters, used in the equations, are properties of the Hydraulic System Properties component used in the model.
ν
m2s
Kinematic viscosity of fluid
nu
ρ
kgm3
Density of fluid
rho
El
Bulk modulus of fluid
See Also
Hydraulics Library
Restrictions
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