Encyclopaedia Index

### Nett-source print-out in RESULT

(Click here to learn how to access and use nett sources in parameterised Q1 files)

The RESULT file contains, below the print-out of the solved and stored variables, a tabulation of the "nett sources" of all the patches which have been used to create sources or boundary conditions.

These nett sources are the sums, for all cells in the patch, of:

CO * ( VAL - VAR ) * "type multiplier"

where:

• CO and VAL are the coefficient and value appropriate to the cell and variable, as specified by the COVAL command in the Q1 file;
• VAR is the value of the solved-for variable in the cell, and
• "type multiplier is unity, or cell volume, or area, etc, according to the type of the patch.

Moreover, the RESULT file also contains, for each solved-for variable:

1. the summation of all the positive sources;
2. the summations of all the negative sources; and
3. the difference between them, which is to say the whole-domain nett source for the variable.

For mass sources at fixed-pressure boundaries, additional information is provided. As well as the nett mass flow through the boundary, the individual positive (In-flow) and negative (out-flow) flows are reported, as shown in this example:

```Nett source of R1 at patch named: OB5 (INLET )  = 5.945001E+00
Nett source of R1 at patch named: OB6 (OUTLET ) =-5.944975E+00 (Mass Out -6.226088E+00 In 2.811145E-01)
pos. sum=5.945001 neg. sum=-5.944975 nett sum=2.574921E-05 ```

For the energy equation in temperature form, the average temperature of the inflow and outflow is reported, as here:

```Nett source of TEM1 at patch named: OB5 (INLET )  = 1.775355E+04 (Average 1.999991E+01)
Nett source of TEM1 at patch named: OB6 (OUTLET ) =-1.820721E+04 (Ave Out 2.729029E+01 In 2.000000E+01)
Nett source of TEM1 at patch named: OC1 (FENCE )  = 5.000002E+02
pos. sum=1.825355E+04 neg. sum=-1.820721E+04 nett sum=46.341797 ```

For other scalars, the average value of the scalar in the in- and out-flow stream is reported.

When EGWF (Earth Generated Wall Functions) is active, the nett friction force on each blockage is also reported.

There is one exception, namely:

1. nett sources which are equal to zero (perhaps because CO has been set to zero, are not printed:

Apart from the physical interest attaching to the nett sources, they also convey valuable information about the extent the which the solution of the equations is adequately converged.

Note that as the pressure forces in the momentum equations are not included in the source sums, the nett sources for momentum are not expected to tend to zero.

Nett Sources have units of mass_per_unit_time * variable. Average values have units of the variable. Typically the units of the sources are:

• U1,V1,W1 - Force - Newtons
• R1 - Mass - kg/s
• TEM1 or H1 - Energy - Watts

### In-Form's nets command

An expression which may be used in In-Form statements is:
nets(dependent-variable name, object or body name)

Here 'nets' stands for 'nett source'.

An example of its use is, in core-library case 249:

```
real(reffor) ! reference force
reffor=refvel*enul/yvlast
(print of lid_force is nets(u1,move)/:reffor:)
```
It compares, and prints to the inforout file, the frictional force on the lid in a lid-driven cavity flow with that which would correspond to an linear velocity profile between lid and floor. How it varies with sweep is shown below.