Local Restriction (IL)
Local narrowing of the flow in the isothermal fluid network.
blockType: AcausalFoundation.IsothermalLiquid.Elements.LocalRestriction
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Local Restriction (IL) Path in the library: |
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Variable Local Restriction (IL) Path in the library: |
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Description
Block Local Restriction (IL) simulates a pressure drop due to a local decrease in the flow area, such as a valve or opening, in an isothermal fluid network.
Ports A and B represent the input and output of the unit Local Restriction (IL). The input signal on the AR port defines the flow section. In addition, you can specify a fixed cross-section as a block parameter.
The block icon changes depending on the value of the Restriction type parameter.
The unit is adiabatic and does not exchange heat with the environment.
Local Restriction (IL) It consists of a narrowing followed by a sudden expansion. At the point of constriction, the liquid accelerates, causing a pressure drop. In the expansion zone, if the Pressure recovery parameter is turned off, the momentum of the accelerated fluid is lost. If the Pressure recovery parameter is enabled, the sudden expansion restores part of the pulse and allows the pressure to rise slightly after a local narrowing of the flow.
Schematic representation of the local constriction
The block equations determine the mass flow through the pressure difference between ports A and B:
where:
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— pressure difference.
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and — pressure at ports A and B respectively.
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— the area of the passage section.
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— the cross-sectional area at ports A and B.
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— the critical pressure drop for the transition between laminar and turbulent flow modes.
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— critical Reynolds number.
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— kinematic viscosity of a liquid at atmospheric pressure.
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— expense ratio.
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— the average density of a mixture of liquids.
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and — the density values of the liquid mixture at ports A and B, respectively. The equations used to calculate the density of a liquid mixture depend on the selected isothermal fluid model.
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— pressure loss coefficient.
Pressure loss coefficient, , depends on the value of the Pressure recovery parameter:
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If Pressure recovery is disabled, then
.
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If Pressure recovery is enabled, then
The area of the passage section, , depends on the value of the constraint type parameter:
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For a variable limit:
,
where — the value of the input signal, and and — the values of the Minimum restriction area and Maximum restriction area block parameters, respectively.
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For a fixed limit — this is the value of the Restriction area parameter.
By default, it is assumed that the cross-sectional area at the entrance and exit is much larger than the passage, which allows you to take the value of the parameter Cross-sectional area at ports A and B, m2 equal to inf And all the members in the equations equal to 0 to increase the efficiency of calculations. Set the actual value for the parameter Cross-sectional area at ports A and B, m2 if the two cross-sectional areas are comparable in size and their ratio affects the flow calculations.
Ports
Entrance
AR is a signal specifying the value of the passage section, m2
scalar
The input signal that sets the value of the flow section. The value is limited by the minimum and maximum limits set by the block parameters.
Dependencies
This port is used only if the Restriction type parameter is set to Variable.
Non-directional
A — inlet or outlet
isothermal liquid
The port of the isothermal fluid corresponds to the inlet or outlet of the local narrowing of the flow. This block has no internal orientation.
B — inlet or outlet
isothermal liquid
The port of the isothermal fluid corresponds to the inlet or outlet of the local narrowing of the flow. This block has no internal orientation.
Parameters
Restriction type — the ability to change the passage section
Variable (by default) | Fixed
Select whether the flow section can change during the simulation.:
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Variable— the input signal on the AR port determines the cross-sectional area, which may change during the simulation. The Minimum restriction area and Maximum restriction area parameters set the lower and upper boundaries of the cross-sectional area. -
Fixed— the cross-sectional area set by the value of the Restriction area parameter remains constant during the simulation. At the same time, the AR port is hidden.
Minimum restriction area — the lower boundary of the cross-sectional area of
1e-10 m2 (default)
The lower boundary of the cross-sectional area. You can use this parameter to represent the leakage area. The input signal AR is limited to this value to prevent further reduction of the cross section.
Dependencies
To use this parameter, set the Restriction type parameter to Variable.
Maximum restriction area — the upper limit of the area of the passage section of the local narrowing of the flow
5e−3 m2 (default)
The upper boundary of the area of the passage section of the local narrowing of the flow. The input signal AR is saturated at this value to prevent a further increase in the cross-sectional area.
Dependencies
To use this parameter, set the Restriction type parameter to Variable.
Restriction area — the area of the passage section normal to the path of local narrowing of the flow
1e−3 m2 (default)
The area of the passage section is normal to the path of local narrowing of the flow.
Dependencies
To use this parameter, set the Restriction type parameter to Fixed.
Cross-sectional area at ports A and B — flow cross-sectional area at ports
Inf (default)
The cross-sectional area of the flow at ports A and B, m2. This area is assumed to be the same for the two ports.
Discharge coefficient — the ratio of the actual mass flow to the theoretical mass flow due to the local narrowing of the flow
0.64 (default)
The ratio of the actual mass flow to the theoretical mass flow through the local narrowing of the flow. An empirical parameter that takes into account the effects of imperfection.
Critical Reynolds number — the Reynolds number for the transition between laminar and turbulent pass modes:q[<br>] 150 (default)
The Reynolds number for the transition between laminar and turbulent modes.
Pressure recovery — accounting for pressure recovery
disabled (by default) | enabled
Determines whether the pressure recovery at the outlet of the local narrowing of the flow will be taken into account.