Flowfield properties may be integrated during the course of a Wind-US run to check convergence and solution quality. The values printed to the list file represent force coefficients F/A_rq_r and moment coefficients M/L_rA_rq_r in the x, y, and z coordinate directions, where F and M are the force and moment, and L_r, A_r, and q_r are the reference values of length, area, and dynamic pressure. Integrated mass and momentum fluxes may also be computed. The values are written into the list output (.lis) file.

The various elements of the LOADS keyword block are defined below. Unless noted otherwise, the keywords apply to both structured and unstructured grids.

PRESSURE [OFFSET] {FREESTREAM | val}

This keyword controls the pressure integration. By default, the code uses P − P_∞ in all pressure integrations, where P_∞ is the static pressure at freestream conditions. This keyword permits the user to specify the pressure offset value, such that:

	FREESTREAM	Use P − P∞
	val	Use P − val

PRINT [PLANES] [TOTALS] [ZONES] [LIFT | DRAG] [FREQUENCY freq] \    [MAKE_FRC file]

This keyword controls the output data from the integration. Options are turned "on" by including the appropriate keyword.

	PLANES		Output the result of the integration for each surface and/or subset specified.
	TOTALS		Output integration grand totals over all the zones at the end of each cycle.
	ZONES		Output integration totals for each zone.
	LIFT | DRAG		Output lift, drag, and side forces instead of (x, y, z) force components. Directions for the lift, drag, and side force components are computed from the angles of attack and yaw specified using the FREESTREAM keyword.
	FREQUENCY		Output integration results (except for grand totals) every freq iterations. The default value is 5.
	MAKE_FRC		Write grand totals to the summary file file at the end of each cycle, in addition to the .lis file. This requires that PRINT TOTALS also be specified.

REFERENCE AREA aref REFERENCE LENGTH lref REFERENCE MOMENT [CENTER] xc yc zc

These keywords specify the reference area aref in square inches; the reference length lref in inches; and the coordinates (xc, yc, zc) of the reference moment center in inches. The default values are 1.0 for aref, 1.0 for lref, and (0.0, 0.0, 0.0) for (xc, yc, zc).

ZONE nzn

This keyword specifies the zone number nzn for the surfaces and/or subsets which follow.

SURFACE {I val | J val | K val} word1 [word2 [word3...]]

This form of the SURFACE keyword applies to structured grids, and specifies the coordinate surface in zone nzn over which the integration is to be performed. The parameter val is a coordinate index specifying the surface.

The word parameters are keywords specifying what flowfield properties are to be computed, plus a couple of additional control values. The following keywords are currently available.

	FORCE		Compute pressure forces.
	MOMENT		Compute moments.
	VISCOUS		Also compute viscous forces (when FORCE is specified) and moments (when MOMENT is specified).
	MASS		Compute mass flow.
	MOMENTUM		Compute momentum.
	NORMAL inorm		inorm = ±1, specifying the desired normal vector direction; +1 for the increasing index direction and −1 for the decreasing index direction. inorm defaults toward the interior of the grid if the integration surface is on a boundary of the zone.
	NOSLIP		Integrate only over points where the total velocity is 0.

At least one flowfield property must be specified. For integration surfaces that are not part of a zonal boundary, the normal direction must also be specified.

Note that when VISCOUS is specified, the viscous forces and moments are printed to the .lis file as separate values; they are not summed with the pressure forces and moments. Note also that you can't compute just the viscous values. E.g., to get the viscous forces you must also get the pressure forces. Specifying just SURFACE J 1 VISCOUS will result in no forces being printed to the .lis file for the j = 1 surface.

SURFACE {I|U} val word1 [word2 [word3...]]

This form of the SURFACE keyword applies to unstructured grids, and specifies the unstructured surface in zone nzn over which the integration is to be performed. The parameter val is the surface number.

The word parameters are keywords specifying what flowfield properties are to be computed. The following keywords are currently available.

	FORCE		Compute pressure forces.
	MOMENT		Compute moments.
	VISCOUS		Also compute viscous forces (when FORCE is specified) and moments (when MOMENT is specified).
	MASS		Compute mass flow.
	MOMENTUM		Compute momentum.
	HEAT		Compute heat flux. This keyword is only available for isothermal walls.

At least one flowfield property must be specified.

SUBSET I range J range K range word1 [word2 [word3...]]

This keyword may be used with structured grids to define a subset of a computational surface in zone nzn over which the integration is to be performed. The range parameters take one of the following forms:

	index1 index2		Starting and ending indices in the specified direction. LAST may be used for the last index.
	ALL		Equivalent to 1 LAST.

For three-dimensional cases, the starting and ending indices for one (and only one) of the I, J, or K parameters must be the same. For two-dimensional cases, the K parameter must be specified as either K 1 1 or K ALL; one or both of the I and J parameters may have different starting and ending indices.

The word parameters are the same as those described above for the SURFACE keyword for structured grids.

Example

   LOADS
      PRESSURE OFFSET 0.0
      PRINT PLANES ZONES TOTALS LIFT FREQUENCY 2
      REFERENCE AREA 100.
      REFERENCE LENGTH 12.
      REFERENCE MOMENT CENTER 35. 36. 78.
      ZONE 4
         SUBSET I ALL J 1 1 K 15 LAST FORCE MOMENT VISCOUS NOSLIP
      ZONE 10
         SURFACE I 1 MOMENTUM MASS
   ENDLOADS