# LINE_SOURCE

Specifies sources on a line.

## Type

AcuSolve Command

## Syntax

LINE_SOURCE("name"){parameters...}

## Qualifier

User-given name.

## Parameters

- lines (array) [no default]
- A three-column array defining the line connectivity.
- radius (real) >0 [=1]
- Effective radius of the line.
- friction_type (enumerated) [=none]
- Type of the friction factor.
- none
- No friction.
- constant or const
- Constant for the entire set. Requires friction.
- piecewise_linear or linear
- Piecewise linear curve fit. Requires friction_curve_fit_values and friction_curve_fit_variable.
- cubic_spline or spline
- Cubic spline curve fit. Requires friction_curve_fit_values and friction_curve_fit_variable.

- friction (real) >=0 [=1]
- Constant value of the friction factor. Used with constant friction type.
- friction_curve_fit_values (array) [={0,1}]
- A two-column array of independent-variable/friction-factor data values. Used with piecewise_linear and cubic_spline friction types.
- friction_curve_fit_variable (enumerated) [=normal_velocity]
- Independent variable of the friction factor curve fit. Used with
piecewise_linear and cubic_spline friction
types.
- normal_velocity
- Velocity component normal to the line.

- friction_multiplier_function (string) [=none]
- User-given name of the multiplier function for scaling the friction factor. If none, no scaling is performed.
- axial_friction_factor (real) >=0 [=10]
- Fraction of the friction factor used for the axial friction factor.
- volume_heat_source_type (enumerated) [=none]
- Type of the heat source per unit volume.
- none
- No volume heat source.
- constant or const
- Constant for the entire set. Requires volume_heat_source.

- volume_heat_source (real) >=0 [=1]
- Constant value of the heat source per unit volume. Used with constant volume heat source type.
- volume_heat_source_multiplier_function (string) [=none]
- User-given name of the multiplier function for scaling the volume heat source. If none, no scaling is performed.
- turbulence_source_type (enumerated) [=none]
- Type of the turbulence source.
- none
- No turbulence source.
- constant or const
- Constant for the entire set. Requires turbulence_source.
- piecewise_linear or linear
- Piecewise linear curve fit. Requires turbulence_source_curve_fit_values and turbulence_source_curve_fit_variable.
- cubic_spline or spline
- Cubic spline curve fit. Requires turbulence_source_curve_fit_values and turbulence_source_curve_fit_variable.

- turbulence_source (real) >=0 [=0]
- Constant value of the turbulence source. Used with constant turbulence source type.
- turbulence_source_curve_fit_values (array) [={0,1}]
- A two-column array of independent-variable/turbulence-source data values. Used with piecewise_linear and cubic_spline turbulence source types.
- turbulence_source_curve_fit_variable (enumerated) [=normal_velocity]
- Independent variable of the turbulence source curve fit. Used with
piecewise_linear and cubic_spline turbulence
source types.
- normal_velocity
- Velocity component normal to the line.

- turbulence_source_multiplier_function (string) [=none]
- User-given name of the multiplier function for scaling the turbulence source. If none, no scaling is performed.
- mesh_motion (string) [=none]
- User-given name of the MESH_MOTION command for specifying mesh displacement boundary conditions on all the nodes in this line. If none, no boundary conditions are imposed.

## Description

This command specifies momentum, heat, and turbulence sources on a line.

```
LINE_SOURCE( "example line source" ) {
lines = { 1001, 1, 2 ;
1002, 3, 4 ;
1003, 5, 6 ; }
radius = 1
friction_type = constant
friction = 1
axial_friction_factor = 10
friction_multiplier_function = none
volume_heat_source_type = constant
volume_heat_source = 2
volume_heat_source_multiplier_function = none
turbulence_source_type = constant
turbulence_source = 0.01
turbulence_source_multiplier_function = none
mesh_motion = none
}
```

```
1001 1 2
1002 3 4
1003 5 6
```

```
LINE_SOURCE( "example line source" ) {
lines = Read( "example.lin" )
...
}
```

The force on the line is defined in terms of the pressure drop in the normal and axial directions:

where p is the fluid pressure;
**a** is the direction parallel to the line;
**n** is the direction of the fluid velocity
projected to the plane normal to the line (that is, the "normal" direction);
f(u_{n}) is the friction factor, given
by friction_type and related parameters (see below);
f_{a}f(u_{n}) is the axial
friction factor; f_{a} is given by
axial_friction_factor; R is
the effective radius, given by radius; is the normal
velocity; is
the axial velocity; and **u** is the fluid
velocity vector. The pressure drop is integrated over the effective volume yielding a
force on the fluid, which is applied only at the nodes on the line.

If friction_type=constant, the friction factor is given by friction.

```
LINE_SOURCE( "curve fit friction factor" ) {
friction_type = piecewise_linear
friction_curve_fit_values = { 0, 10.685 ;
5, 3.291 ;
10, 1.996 ;
15, 1.495 ;
20, 1.220 ;
30, 0.920 ;
40, 0.756 ;
50, 0.650 ; }
friction_curve_fit_variable = normal_velocity
...
}
```

defines the friction factor as a function of the normal velocity (that is, velocity in the direction of the heat exchanger). The friction_curve_fit_values parameter is a two-column array corresponding to the independent variable and the friction factor. The independent variable values must be in ascending order. The limit point values of the curve fit are used when friction_curve_fit_variable falls outside of the curve fit limits.

```
0 10.685
5 3.291
10 1.996
15 1.495
20 1.220
30 0.920
40 0.756
50 0.650
```

```
LINE_SOURCE( "curve fit friction factor" ) {
friction_type = piecewise_linear
friction_curve_fit_values = Read( "friction.fit" )
friction_curve_fit_variable = normal_velocity
...
}
```

A volumetric heat source for the temperature equation is given by volume_heat_source. This has the same units and effect as the VOLUME_HEAT_SOURCE command. The only difference is that here the heat source is integrated over the effective volume and applied only on the nodes of the line.

For the Spalart-Allmaras and Detached Eddy Simulation turbulence models, a turbulence line source is given by:

where f_{t}(u_{n}) is the turbulence source,
given by turbulence_source_type and related parameters; and
s is an effective volumetric source term in the
turbulence model equation. The latter is integrated over the effective volume and
applied only on the nodes of the line.

If turbulence_source_type=constant, the turbulence source is given by turbulence_source. A piecewise_linear or cubic_spline turbulence source type may be used to define the turbulence source as a function of the normal velocity.

The friction_multiplier_function, volume_heat_source_multiplier_function and turbulence_source_multiplier_function parameters may be used to scale the friction factor, volume heat source, and turbulence source, respectively. The value of each of these parameters refers to the user given name of a MULTIPLIER_FUNCTION command in the input file.

```
LINE_SOURCE( "rotating fan" ) {
mesh_motion = "rotating fan"
...
}
MESH_MOTION( "rotating fan" ) {
type = rotation
rotation_center = { 0, 0, 0 }
angular_velocity = { 0, 3, 0 }
}
```