Surface Integral Output

Surface Integral Output#

Surface Integral Output computes surface integrals of custom user variables on selected surfaces and can optionally report moving statistics over time.

Available Options#

Option	Description	Applicable
Output fields	Custom user variables to integrate over the assigned surfaces	always
Statistics function	Optional moving statistic applied to the integrated values	always
Moving window size	Window size for moving statistics (in output data points)	when Statistics function is not `None`
Start step	Step at which to start statistics calculation	when Statistics function is not `None`
Assigned surfaces	Surfaces used for the integral	always

Detailed Descriptions#

Output fields#

The custom user variables to integrate over the selected surfaces.

Required (at least one field must be selected)
Allowed fields: Custom user variables only
Example: PressureForce, HingeTorqueZ

Note: Surface Integral Output only accepts custom user variables. Define them in Variable Settings (Custom variables tab).

Statistics function#

Optional moving statistic applied to the integrated values. When set to None, raw integral values are reported.

Default: None
Options:
- None - No statistics processing
- Mean - Moving average
- Min - Minimum in the window
- Max - Maximum in the window
- Standard deviation - Sample standard deviation (Bessel’s correction)
- Deviation - Range (maximum minus minimum) in the window

Moving window size#

The number of output data points used in the moving statistics window.

Default: 10
Minimum value: 2

Note: For steady simulations, the solver typically outputs a data point every 10 pseudo steps. For unsteady simulations, it outputs every physical step.

Start step#

The number of steps to skip before statistics calculation begins.

Default: 0

Note: For steady simulations, this value is rounded up to the nearest multiple of 10 (based on output cadence).

Assigned surfaces#

The surfaces on which the integral is computed.

Required: Yes (at least one surface must be selected)
Supported surface types:
- Simulation surfaces (mesh boundaries)
- Imported sample surfaces

Notes:

Import sample surfaces in the Entities browser before selecting them. See Sample Surfaces.

Do not mix simulation surfaces and imported sample surfaces in a single Surface Integral Output. Create separate outputs if you need both.

Examples#

The two worked setups below show how to combine a custom user variable with assigned surfaces to integrate a quantity of interest. In every case the custom variable is defined first in Variable Settings (Custom variables tab), then selected under Output fields and integrated over the surfaces chosen under Assigned surfaces.

(a) Hinge moment#

Custom variable: Define a user variable for the moment of the local surface force (pressure + viscous) about the hinge axis, e.g. the cross product of the position vector relative to a point on the hinge line with the combined pressure and wall-shear force, projected onto the hinge-axis direction: HingeMoment = dot(cross(r - r_hinge, PressureForce + ViscousForce), hinge_axis).
Assigned surfaces: The wall surfaces of the control surface that rotates about the hinge (e.g. the flap or aileron) only.
Result: Integrating this variable over those surfaces yields the hinge moment, i.e. the moment required to hold (or actuate) the control surface about its hinge line.

(b) Surface heat flux#

Custom variable: Define a user variable for the local wall heat flux (the conductive heat flux normal to the wall, e.g. WallHeatFlux).
Assigned surfaces: The wall surface(s) of interest whose heat transfer you want to quantify.
Result: Integrating this variable over those surfaces yields the total heat transfer rate through them.