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Orifice

Fixed orifice

 

Description

Equations

Variables

Connections

Parameters

Description

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 (Cdmax) 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.

Equations

p=pApB

Acs=A

Orifice Fluid Equations

{p=π4ρνqCd2AcsπAcs16q4π2Acs2ν4+ReCr414Use constant Cd=trueq=Cdmaxtanh4Acsπ2pρνCritnoAcs2pρsignpotherwise

Optional Volume Equations

VfA={Va1+pAElUse volume A=true0otherwiseVfB={Vb1+pBElUse volume B=true0otherwise

q=qAqVA=qBqVB

qVA={dVfAdtUse volume A=true0otherwiseqVB={dVfBdtUse volume B=true0otherwise

Variables

Name

Units

Description

Modelica ID

p

Pa

Pressure drop from A to B

p

pX

Pa

Pressure at port X

pX

q

m3s

Flow rate from A to B

q

qX

m3s

Flow into port X

qX

qVX

m3s

Flow rate into port X's optional volume

qVX

VfX

m3

Effective volume at port X

VfX

Connections

Name

Description

Modelica ID

portA

Upstream hydraulic port

portA

portB

Downstream hydraulic port

portB

Parameters

General

Name

Default

Units

Description

Modelica ID

A

1·10−6

m2

Area of opening

A

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

Cd

ReCr

12

 

Reynolds number at critical flow; used when Use constant Cd is true

ReCr

Coeff

0.7

 

Maximum flow-discharge coefficient; used when Use constant Cd is false

Coeff

Critno

1000

 

Critical flow number; used when Use constant Cd is false

Crit_no

Optional Volumes

Name

Default

Units

Description

Modelica ID

Use volume A

false

 

True (checked) means a hydraulic volume chamber is added to portA

useVolumeA

VA

1·10−6

m3

Volume of chamber A

Va

Use volume B

false

 

True (checked) means a hydraulic volume chamber is added to portB

useVolumeB

VB

1·10−6

m3

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.

Name

Units

Description

Modelica ID

ν

m2s

Kinematic viscosity of fluid

nu

ρ

kgm3

Density of fluid

rho

El

Pa

Bulk modulus of fluid

El

See Also

Hydraulics Library

Restrictions