Force Coefficient

The force coefficient report calculates a dimensionless force in a user-specified direction, and can be used for lift and drag calculations.

It is represented in the simulation tree by a node, which has its own properties but is subject to the report node’s pop-up menu. It also has an expert property for obtaining values using bands.

The force coefficient of a surface is defined as follows:

图 1. EQUATION_DISPLAY

C_{D} = \frac{\sum_{f}^{} (f_{f}^{p r e s s u r e} + f_{f}^{s h e a r}) \cdot n_{D}}{\frac{1}{2} (ρ_{r e f} v_{r e f}^{2} a_{r e f})}

(429)

where $f_{f}^{p r e s s u r e}$ and $f_{f}^{s h e a r}$ are the pressure and shear force vectors on the surface face $f$ , and $ρ_{r e f}$ , $v_{r e f}$ and $a_{r e f}$ are the reference density, velocity, and area, respectively. $n_{D}$ is a user-specified direction vector. To compute drag, for example, specify the direction vector as the direction of travel, and for lift, specify the direction as normal to the direction of travel.

The pressure force vector on surface face is computed as:

图 2. EQUATION_DISPLAY

f_{f}^{p r e s s u r e} = (p_{f} - p_{r e f}) a_{f}

(430)

where $p_{f}$ is the face static pressure $a_{f}$ is the face area vector, and $p_{r e f}$ is the reference pressure. As defined, this is the force that the fluid exerts on the surface. The note on reference pressure provided for the Force report applies here.

The shear force on surface face $f$ is computed as:

图 3. EQUATION_DISPLAY

f_{f}^{s h e a f} = - T_{f} \cdot a_{f}

(431)

where $T_{f}$ is the stress tensor at face $f$ . This shear force is exerted on the surface by the fluid.

Force Coefficient Report Properties

In addition to constants, you can enter field function syntax directly.


Coordinate System	A list of coordinate systems in the simulation for use by this report.
Direction	A Cartesian vector that indicates the direction in which the force is computed.
Force Option	The type of force to be computed.
	Shear	Only the force due to shear, $f_{f}^{s h e a r}$ in Eqn. (429) is considered in the computation.
	Pressure	Only the force due to pressure, $f_{f}^{p r e s s u r e}$ in Eqn. (429) is considered in the computation.
	Pressure & Shear	Both pressure and shear forces, $f_{f}^{p r e s s u r e}$ and $f_{f}^{s h e a r}$ , are considered in the computation of Eqn. (429).
Parts	A list of parts that is used as the source for this report. Opens the in-place part selector for editing. The (property customizer) button activates a modeless version of the selector dialog (it lets you interact with other portions of the workspace).
Reference Area	The reference area for the computation of Eqn. (429).
Reference Density	The reference density for the computation of Eqn. (429).
Reference Pressure	The reference pressure for the computation of Eqn. (430).
Reference Velocity	The reference velocity for the computation of Eqn. (429).
Units	Units that are used for specifying the quantity.

Force Coefficient Report Expert Properties


Pressure Option	This property lets you exclude the hydrostatic pressure. For details, see Options for Excluding Hydrostatic Pressure from Fluid Loads Calculations.
Number of Bands	A text entry for the number of bands into which to divide the model.
Representation	Selects a representation. Additional selections appear as representations that are added to the simulation.
Smooth Values	When this property is activated, the report is calculated using node (interpolated) values of the chosen quantity rather than cell values.
Account for Idealization	Applies idealizations related to the chosen parts before computing. For details, see Obtaining Whole Domain Reports through Idealizations.