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.

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:

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

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).

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

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. The following keywords are currently available.

Two additional word parameters may be used to control values computed on structured grids.

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.

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.

At least one flowfield property must be specified.

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:

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.

This keyword may be used to reference a named surface group, which is stored in the common grid (.cgd) file. Since surface groups may contain surfaces from multiple zones, the ZONE keyword is not needed.

The word parameters used to specify flowfield properties 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.
      GROUP wing FORCE MOMENT VISCOUS
      ZONE 4
         SUBSET I ALL J 1 1 K 15 LAST FORCE MOMENT VISCOUS NOSLIP
      ZONE 10
         SURFACE I 1 MOMENTUM MASS
   ENDLOADS

Extracting Loads from the List Output File

As discussed above, integrated values are output to the *.lis file for four types of domain regions: Planes, Groups, Zones, and Totals. For each domain type, several properties may be requested: Force, Moment, Mass, Momentum, and Heat Flux. Each line of loads data that is written to the *.lis file contains: an identifier, one or more integer values, one or more real values, and units (if any). The list of valid identifiers are shown below.

Each domain type uses a particular identifier prefix. The integer values written to the load record include the iteration number, zone number, and load plane number (from the list of load planes specified in the *.dat file) as appropriate. This information can be summarized as follows:

The real values written to the load record represent the integrated values of the physical property being reported. For vector quantities, values are written for each component. Units are included for dimensional values, but not for coefficient data. Note again that the default force and moment coefficients are based solely on the pressure terms. Only when VISCOUS is specified are the additional viscous coefficients output. The table below summarizes the property values that are output.

The resplt utility can be used to filter and extract the loads data to a GENPLOT file. This method gives the user control over which properties are extracted and for which domain regions. Using techniques similar to those described in the Monitor Convergence section of the tutorial, one can plot the GENPLOT file with CFPOST. Since GENPLOT files are text-based, they can also be easily manipulated for use in other plotting applications. The Genplot File Format is described in the CFPOST User's Guide.

See Also: FIXED_CL, POSTPROC, WALL FUNCTION,