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Fluid Inertia

(To be removed) Pressure differential across tube or channel due to change in fluid velocity

The Hydraulic library will be removed in a future release. Use the Isothermal Liquid library instead. (since R2020a)

For more information on updating your models, see Upgrading Hydraulic Models to Use Isothermal Liquid Blocks.


Hydraulic Elements

  • Fluid Inertia block


The Fluid Inertia block models pressure differential, due to change in fluid velocity, across a fluid passage of constant cross-sectional area. The pressure differential is determined according to the following equation:



pPressure differential
ρFluid density
LPassage length
APassage area
qFlow rate

Use this block in various pipe or channel models that require fluid inertia to be accounted for.

The block positive direction is from port A to port B. This means that the flow rate is positive if it flows from A to B.


To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

Assumptions and Limitations

Fluid density remains constant.


Passage area

Fluid passage cross-sectional area. The default value is 8e-5 m^2.

Passage length

Length of the fluid passage. The default value is 1 m.

Initial flow rate

Initial flow rate through the passage. This parameter specifies the initial condition for use in computing the block's initial state at the beginning of a simulation run. For more information, see Initial Conditions Computation. The default value is 0.

Global Parameters

Parameter determined by the type of working fluid:

  • Fluid density

Use the Hydraulic Fluid (Simscape Fluids) block or the Custom Hydraulic Fluid block to specify the fluid properties.


The block has the following ports:


Hydraulic conserving port associated with the passage inlet.


Hydraulic conserving port associated with the passage outlet.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2007a

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