Defining the Fluid Flow In and Out of Fluid Cavities

You can define the fluid flow between two fluid cavities or between a fluid cavity and its environment.

You can define an exchange for two-dimensional, three-dimensional, and axisymmetric models.

This task shows you how to:

Define Fluid Exchange Based on Bulk Viscosity
Define Fluid Exchange Based on Mass Flux, Volume Flux, or Energy Flux
Define Fluid Exchange Based on Leakage of Mass, Volume, Energy, or Through Fabric
Define Fluid Exchange Based on Discharge Through an Orifice
Define Fluid Exchange Based on User Subroutines

Before you begin: Define the fluid cavities that exchange fluid or the fluid cavity that exchanges fluid with its environment, as described in Defining Fluid Cavities.

Define Fluid Exchange Based on Bulk Viscosity

From the Abstractions section of the action bar, click Fluid Exchange .
Optional: Enter a descriptive Name.
Specify the fluid cavities by doing the following:
- For an exchange between two fluid cavities, specify the cavities as the Primary fluid cavity and the Secondary fluid cavity.
- For an exchange between a single fluid cavity and its environment, specify the only fluid cavity as the Primary fluid cavity and accept the default setting of to environment as the Secondary fluid cavity.
Enter a value in the Effective area field, which is the cross-sectional area through which fluid exchanges.
The app considers the effective area only during explicit dynamic steps.
From the Definition options, select Bulk viscosity.
Select Use pressure-dependent data to specify fluid exchange data that changes as a function of pressure.
Select Use temperature-dependent data to specify fluid exchange data that changes as a function of temperature.
From the Number of field variables options, specify a number of field variables to specify fluid exchange that changes as a function of field variables.
Specify the Viscous resistance coefficient, which determines the viscosity-related resistance to fluid exchange.
Specify the Hydrodynamic resistance coefficient, which determines the hydrodynamic-related resistance to fluid exchange.
For explicit dynamic steps, expand the Advanced options for Explicit analysis section and specify any of the following options to describe explicit dynamic behavior in fluid exchange:
1. To model the effects of fluid cavity rupture, do the following:
  1. Select Allow rupture to allow fluid and heat energy to be exchanged through failed elements.
  2. Enter a value in the Rupture area ratio field, which specifies the fraction of the fluid exchange cross-sectional area that consists of failed elements.
2. From the Apply cavity pressure to list, select one of the following:
  - Select Surface to generate forces at all fluid exchange surface nodes.
  - Select Perimeter of surface to generate forces on the nodes on the perimeter of the fluid exchange surface only.
3. From the Effective leakage area options, specify either the size of the effective area or define the constants to specify the effective leakage area with a user subroutine.
  The effective leakage area can represent values for leakage components such as the size of an exhaust orifice, the area of the porous fabric that encloses the fluid cavity, or the size of a pipe between the cavities.
4. Select the Exchange surface, the surface that represents the leakage area or determines the degree of blockage arising from an obstruction between the contacting surfaces.
Click OK.
For nonaxisymmetric models, a glyph appears with its arrowheads oriented along the global x-axis. For axisymmetric models, a glyph appears with its arrowheads oriented along the r-axis.

Define Fluid Exchange Based on Mass Flux, Volume Flux, or Energy Flux

From the Abstractions section of the action bar, click Fluid Exchange .
Optional: Enter a descriptive Name.
Specify the fluid cavities by doing the following:
- For an exchange between two fluid cavities, specify the cavities as the Primary fluid cavity and the Secondary fluid cavity.
- For an exchange between a single fluid cavity and its environment, specify the only fluid cavity as the Primary fluid cavity and accept the default setting of to environment as the Secondary fluid cavity.
Enter a value in the Effective area field, which is the cross-sectional area through which fluid exchanges.
The app considers the effective area only during explicit dynamic steps.

From the Definition options, select one of the following:

Option	Description
Mass flux	The fluid exchange rate is based on the mass flow rate per unit area for the effective area.
Volume flux	The fluid exchange rate is based on the volumetric flow rate per unit area for the effective area.
Energy flux	The fluid exchange rate is based on the energy flux per unit area for the effective area.

Specify the mass flux rate, volume flux rate, or energy flux rate.
For explicit dynamics steps, expand the Advanced options for Explicit analysis section and specify any of the following options to describe explicit dynamics behavior in fluid exchange:
1. To model the effects of fluid cavity rupture, do the following:
  1. Select Allow rupture to allow fluid and heat energy to be exchanged through failed elements.
  2. Enter a value in the Rupture area ratio field, which specifies the fraction of the fluid exchange cross-sectional area that consists of failed elements.
2. From the Apply cavity pressure to list, select one of the following:
  - Select Surface to generate forces at all fluid exchange surface nodes.
  - Select Perimeter of surface to generate forces on the nodes on the perimeter of the fluid exchange surface only.
3. From the Effective leakage area options, specify either the size of the effective area or define the constants to specify the effective leakage area with a user subroutine.
  The effective leakage area can represent values for leakage components such as the size of an exhaust orifice, the area of the porous fabric that encloses the fluid cavity, or the size of a pipe between the cavities.
4. Select the Exchange surface, the surface that represents the leakage area or determines the degree of blockage arising from an obstruction between the contacting surfaces.
Click OK.
For nonaxisymmetric models, a glyph appears with its arrowheads oriented along the global x-axis. For axisymmetric models, a glyph appears with its arrowheads oriented along the r-axis.

Define Fluid Exchange Based on Leakage of Mass, Volume, Energy, or Through Fabric

From the Abstractions section of the action bar, click Fluid Exchange .
Optional: Enter a descriptive Name.
Specify the fluid cavities by doing the following:
- For an exchange between two fluid cavities, specify the cavities as the Primary fluid cavity and the Secondary fluid cavity.
- For an exchange between a single fluid cavity and its environment, specify the only fluid cavity as the Primary fluid cavity and accept the default setting of to environment as the Secondary fluid cavity.
Enter a value in the Effective area field, which is the cross-sectional area through which fluid exchanges.
The app considers the effective area only during explicit dynamic steps.

From the Definition options, select one of the following:

Option	Description
Mass rate leakage	The fluid exchange rate is based on the mass rate of flow out of one fluid cavity as a function of the pressure difference between the fluid cavities or between the leaking fluid cavity and the environment.
Volume rate leakage	The fluid exchange rate is based on the volumetric rate of volume flow out of one fluid cavity as a function of the pressure difference between the fluid cavities or between the leaking fluid cavity and the environment.
Energy rate leakage	The fluid exchange rate is based on the energy rate of volume flow out of one fluid cavity as a function of the pressure difference between the fluid cavities or between the leaking fluid cavity and the environment.
Fabric leakage	The fluid exchange rate is based on the mass flow rate of fluid through the fabric between the fluid cavities or between the leaking fluid cavity and the environment.

Optional: Select Use pressure-dependent data to specify fluid exchange data that changes as a function of pressure.
Optional: Select Use temperature-dependent data to specify fluid exchange data that changes as a function of temperature.
Optional: From the Number of field variables options, specify a number of field variables to specify fluid exchange that changes as a function of field variables.
For explicit dynamic steps, expand the Advanced options for Explicit analysis section and specify any of the following options to describe explicit dynamics behavior in fluid exchange:
1. To model the effects of fluid cavity rupture, do the following:
  1. Select Allow rupture to allow fluid and heat energy to be exchanged through failed elements.
  2. Enter a value in the Rupture area ratio field, which specifies the fraction of the fluid exchange cross-sectional area that consists of failed elements.
2. From the Apply cavity pressure to list, select one of the following:
  - Select Surface to generate forces at all fluid exchange surface nodes.
  - Select Perimeter of surface to generate forces on the nodes on the perimeter of the fluid exchange surface only.
3. From the Effective leakage area options, specify either the size of the effective area or define the constants to specify the effective leakage area with a user subroutine.
  The effective leakage area can represent values for leakage components such as the size of an exhaust orifice, the area of the porous fabric that encloses the fluid cavity, or the size of a pipe between the cavities.
4. Select the Exchange surface, the surface that represents the leakage area or determines the degree of blockage arising from an obstruction between the contacting surfaces.
Click OK.
For nonaxisymmetric models, a glyph appears with its arrowheads oriented along the global x-axis. For axisymmetric models, a glyph appears with its arrowheads oriented along the r-axis.

Define Fluid Exchange Based on Discharge Through an Orifice

From the Abstractions section of the action bar, click Fluid Exchange .
Optional: Enter a descriptive Name.
Specify the fluid cavities by doing the following:
- For an exchange between two fluid cavities, specify the cavities as the Primary fluid cavity and the Secondary fluid cavity.
- For an exchange between a single fluid cavity and its environment, specify the only fluid cavity as Primary fluid cavity and accept the default setting of to environment as Secondary fluid cavity.
Enter a value in the Effective area field, which is the cross-sectional area through which fluid exchanges.
The app considers the effective area only during explicit dynamic steps.
From the Definition options, select Orifice.
Select Use pressure-dependent data to specify fluid exchange data that changes as a function of pressure.
Select Use temperature-dependent data to specify fluid exchange data that changes as a function of temperature.
From the Number of field variables options, specify a number of field variables to specify fluid exchange that changes as a function of field variables.
Specify the Discharge coefficient, which modifies the exhaust or leakage surface area.
For explicit dynamic steps, expand the Advanced options for Explicit analysis section and specify any of the following options to describe explicit dynamics behavior in fluid exchange:
1. To model the effects of fluid cavity rupture, do the following:
  1. Select Allow rupture to allow fluid and heat energy to be exchanged through failed elements.
  2. Enter a value in the Rupture area ratio field, which specifies the fraction of the fluid exchange cross-sectional area that consists of failed elements.
2. From the Apply cavity pressure to list, select one of the following:
  - Select Surface to generate forces at all fluid exchange surface nodes.
  - Select Perimeter of surface to generate forces on the nodes on the perimeter of the fluid exchange surface only.
3. From the Effective leakage area options, specify either the size of the effective area or define the constants to specify the effective leakage area with a user subroutine.
  The effective leakage area can represent values for leakage components such as the size of an exhaust orifice, the area of the porous fabric that encloses the fluid cavity, or the size of a pipe between the cavities.
4. Select the Exchange surface, the surface that represents the leakage area or determines the degree of blockage arising from an obstruction between the contacting surfaces.
Click OK.
For nonaxisymmetric models, a glyph appears with its arrowheads oriented along the global x-axis. For axisymmetric models, a glyph appears with its arrowheads oriented along the r-axis.

Define Fluid Exchange Based on User Subroutines

From the Abstractions section of the action bar, click Fluid Exchange .
Optional: Enter a descriptive Name.
Specify the fluid cavities by doing the following:
- For an exchange between two fluid cavities, specify the cavities as the Primary fluid cavity and the Secondary fluid cavity.
- For an exchange between a single fluid cavity and its environment, specify the only fluid cavity as the Primary fluid cavity and accept the default setting of to environment as the Secondary fluid cavity.
Enter a value in the Effective area field, which is the cross-sectional area through which fluid exchanges.
The app considers the effective area only during explicit dynamic steps.
From the Definition options, select User.
Specify the Number of solution-dependent state variables for which you want to provide leakage data, and then enter the data in the table.
For explicit dynamic steps, expand the Advanced options for Explicit analysis section and specify any of the following options to describe explicit dynamics behavior in fluid exchange:
1. To model the effects of fluid cavity rupture, do the following:
  1. Select Allow rupture to allow fluid and heat energy to be exchanged through failed elements.
  2. Enter a value in the Rupture area ratio field, which specifies the fraction of the fluid exchange cross-sectional area that consists of failed elements.
2. From the Apply cavity pressure to list, select one of the following:
  - Select Surface to generate forces at all fluid exchange surface nodes.
  - Select Perimeter of surface to generate forces on the nodes on the perimeter of the fluid exchange surface only.
3. From the Effective leakage area options, specify either the size of the effective area or define the constants to specify the effective leakage area with a user subroutine.
  The effective leakage area can represent values for leakage components such as the size of an exhaust orifice, the area of the porous fabric that encloses the fluid cavity, or the size of a pipe between the cavities.
4. Select the Exchange surface, the surface that represents the leakage area or determines the degree of blockage arising from an obstruction between the contacting surfaces.
Click OK.
For nonaxisymmetric models, a glyph appears with its arrowheads oriented along the global x-axis. For axisymmetric models, a glyph appears with its arrowheads oriented along the r-axis.