Variable Overlapping Orifice (IL)
An opening formed by open segments with variable overlap in an isothermal liquid network.
Description
The Variable Overlapping Orifice (IL) unit simulates flow through circular orifices with different overlapping areas, e.g. through a movable sleeve in a fixed housing. The overlapping orifices can have different diameters, but the additional orifices along the spool or sleeve have the same diameter.
Overlapping area
The flow rate depends on the variable opening area created by the overlapping openings in the sleeve and body. This instantaneous opening area is calculated as:
where
-
- is the diameter of the smaller hole;
-
- diameter of the larger hole;
-
- absolute distance between the hole centres, calculated from the value of the instantaneous position of the sleeve in the port S and the value of the parameter Sleeve position when holes are concentric, :
If the holes on the sleeve and the body have the same diameter, the overlapping area becomes equal:
At the closest and furthest points between hole centres, the numerical stability of the simulation can be ensured by adjusting the Smoothing factor parameter in the block. The block applies a smoothing function to the normalised hole centre spacing,
The function smoothly changes the normalised hole centre distance from 0 to 1.
Mass flow equation
The flow through a pair of orifices can be determined from the pressure-flow relationship:
,
where
-
- is the Discharge coefficient;
-
- open orifice area, ;
-
- cross-sectional area at inlet and outlet ports A and B Cross-sectional area at ports A and B;
-
- average liquid density.
Pressure loss describes the reduction in pressure due to a decrease in cross-sectional area. The pressure loss coefficient is calculated as:
.
The Pressure recovery takes into account the increase in pressure at the orifice outlet due to the increase in cross-sectional area. If it is not necessary to take this effect into account, set Pressure recovery to off, in which case will be set to `1'.
The critical pressure drop is determined from the value of the critical Reynolds number Critical Reynolds number , which is the transition point between laminar and turbulent fluid flow:
.
Ports
Conserving
#
A
—
isothermal liquid port
isothermal liquid
Details
isothermal liquid port, corresponds to the inlet or outlet of the orifice.
| Program usage name |
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#
B
—
isothermal liquid port
isothermal liquid
Details
isothermal liquid port, corresponds to the inlet or outlet of the orifice.
| Program usage name |
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Input
#
S
—
sleeve displacement, m
scalar
Details
Position of the cartridge case relative to the body in m.
| Data types |
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| Complex numbers support |
No |
Parameters
Parameters
#
Sleeve hole diameter —
sleeve bore diameter
m | cm | ft | in | km | mi | mm | um | yd
Details
Diameter of the bore in the movable element.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Case hole diameter —
housing bore diameter
m | cm | ft | in | km | mi | mm | um | yd
Details
Diameter of the hole in the fixed element.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Sleeve position when holes are concentric —
position of the movable element when the hole centres are aligned
m | cm | ft | in | km | mi | mm | um | yd
Details
The position of the movable element when the hole centres are aligned. This parameter is used to determine the instantaneous overlap between the moving and stationary holes during simulation by comparing it to the signal received at the S port.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Number of interacting pairs — number of pairs of overlapping holes
Details
Number of overlapping hole pairs. The sleeve-hull pairs need not be aligned in the physical equipment being modelled.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Leakage area —
leakage area
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2
Details
The sum of the areas of all gaps when the holes are completely covered. Any area smaller than this value is equated to the specified leakage area. This contributes to the stability of the numerical solution by maintaining flow continuity.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
#
Cross-sectional area at ports A and B —
area at the inlet and outlet of the ports
m^2 | cm^2 | ft^2 | in^2 | km^2 | mi^2 | mm^2 | um^2 | yd^2
Details
The cross-sectional area at the inlet and outlet ports A and B. This area is used in calculating the mass flow rate through the port.
| Values |
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| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Discharge coefficient — flow coefficient
Details
The correction factor is the ratio of the actual mass flow rate to the theoretical mass flow rate through the orifice.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Critical Reynolds number — upper limit of Reynolds number for laminar flow
Details
The Reynolds number at which the laminar flow regime through the orifice is maintained.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Smoothing factor — numerical smoothing factor
Details
A continuous smoothing factor that provides a smooth variation of the opening area by correcting the orifice characteristic in the nearly open and nearly closed positions. Set a non-zero value less than one to increase the stability of the simulation in these modes.
| Default value |
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| Program usage name |
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| Evaluatable |
Yes |
# Pressure recovery — taking into account the pressure rise during the expansion of the area
Details
Determines whether pressure rise is taken into account when fluid flows from a smaller cross-sectional area to a larger cross-sectional area.
If Pressure recovery is unchecked, this pressure increase is not taken into account.
| Default value |
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| Program usage name |
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| Evaluatable |
No |